WPF Tutorial

Concepts of WPF:

Introduction to XAML

XAML stands for Extensible Application Markup Language. Its a simple language based on

XML to create and initialize .NET objects with hierarchical relations. Altough it was originally

invented for WPF it can by used to create any kind of object trees.

Today XAML is used to create user interfaces in WPF, Silverlight, declare workflows in WF

and for electronic paper in the XPS standard.

All classes in WPF have parameterless constructors and make excessive usage of properties.

That is done to make it perfectly fit for XML languages like XAML.

Advantages of XAML

All you can do in XAML can also be done in code. XAML ist just another way to create and

initialize objects. You can use WPF without using XAML. It's up to you if you want to declare

it in XAML or write it in code. Declare your UI in XAML has some advantages:

XAML code is short and clear to read

Separation of designer code and logic

Graphical design tools like Expression Blend require XAML as source.

The separation of XAML and UI logic allows it to clearly separate the roles of designer

and developer.

XAML vs. Code

As an example we build a simple StackPanel with a textblock and a button in XAML and

compare it to the same code in C#.

<StackPanel>

<TextBlock Margin="20">Welcome to the World of XAML</TextBlock>

<Button Margin="10" HorizontalAlignment="Right">OK</Button>

</StackPanel>

The same expressed in C# will look like this:

// Create the StackPanel

StackPanel stackPanel = new StackPanel();

this.Content = stackPanel;

// Create the TextBlock

TextBlock textBlock = new TextBlock();

textBlock.Margin = new Thickness(10);

textBlock.Text = "Welcome to the World of XAML";

stackPanel.Children.Add(textBlock);

// Create the Button

Button button = new Button();

button.Margin= new Thickness(20);

button.Content = "OK";

stackPanel.Children.Add(button);

As you can see is the XAML version much shorter and clearer to read. And that's the power

of XAMLs expressiveness.

Properties as Elements

Properties are normally written inline as known from XML <Button Content="OK" />. But

what if we want to put a more complex object as content like an image that has properties

itself or maybe a whole grid panel? To do that we can use the property element syntax. This

allows us to extract the property as an own chlild element.

<Button>

<Button.Content>

<Image Source="Images/OK.png" Width="50" Height="50" />

</Button.Content>

</Button>

Implicit Type conversion

A very powerful construct of WPF are implicit type converters. They do their work silently in

the background. When you declare a BorderBrush, the word "Blue" is only a string. The

implicit BrushConverter makes a System.Windows.Media.Brushes.Blue out of it. The same

regards to the border thickness that is beeing converted implicit into a Thickness object.

WPF includes a lot of type converters for built-in classes, but you can also write type

converters for your own classses.

<Border BorderBrush="Blue" BorderThickness="0,10">

</Border>

Markup Extensions

Markup extensions are dynamic placeholders for attribute values in XAML. They resolve the

value of a property at runtime. Markup extensions are surrouded by curly braces (Example:

Background="{StaticResource NormalBackgroundBrush}"). WPF has some built-in markup

extensions, but you can write your own, by deriving from MarkupExtension. These are the

built-in markup extensions:

Binding

To bind the values of two properties together.

StaticResource

One time lookup of a resource entry

DynamicResource

Auto updating lookup of a resource entry

TemplateBinding

To bind a property of a control template to a dependency property of the control

x:Static

Resolve the value of a static property.

x:Null

Return null

The first identifier within a pair of curly braces is the name of the extension. All preciding

identifiers are named parameters in the form of Property=Value. The following example

shows a label whose Content is bound to the Text of the textbox. When you type a text into

the text box, the text property changes and the binding markup extension automatically

updates the content of the label.

<TextBox x:Name="textBox"/>

<Label Content="{Binding Text, ElementName=textBox}"/>

Namespaces

At the beginning of every XAML file you need to include two namespaces.

The first is http://schemas.microsoft.com/winfx/2006/xaml/presentation. It is mapped to all

wpf controls in System.Windows.Controls.

The second is http://schemas.microsoft.com/winfx/2006/xaml it is mapped to

System.Windows.Markup that defines the XAML keywords.

The mapping between an XML namespace and a CLR namespace is done by the

XmlnsDefinition attribute at assembly level. You can also directly include a CLR namespace

in XAML by using the clr-namespace: prefix.

<Window xmlns=”http://schemas.microsoft.com/winfx/2006/xaml/presentation”

xmlns:x=”http://schemas.microsoft.com/winfx/2006/xaml”>

</Window>

Logical- and Visual Tree

Introduction

Elements of a WPF user interface are hierarchically related. This relation is called the

LogicalTree. The template of one element consists of multiple visual elements. This tree is

called the VisualTree. WPF differs between those two trees, because for some problems

you only need the logical elements and for other problems you want all elements.

<Window>

<Grid>

<Label Content="Label" />

<Button Content="Button" />

</Grid>

</Window>

Why do we need two different kind of trees?

A WPF control consists of multiple, more primitive controls. A button - for example - consists

of a border, a rectangle and a content presenter. These controls are visual children of the

button.

When WPF renders the button, the element itself has no appearance, but it iterates through

the visual tree and renders the visual children of it. This hierarchical relation can also be

used to do hit-testing, layout etc.

But sometimes you are not interested in the borders and rectangles of a controls' template.

Particulary because the template can be replaced, and so you should not relate on the visual

tree structure! Because of that you want a more robust tree that only contains the "real"

controls - and not all the template parts. And that is the eligibility for the logical tree.

The Logical Tree

The logical tree describes the relations between elements of the user interface. The logical

tree is responsible for:

Inherit DependencyProperty values

Resolving DynamicResources references

Looking up element names for bindings

Forwaring RoutedEvents

The Visual Tree

The visual tree contains all logical elements including all visual elements of the template of

each element.<BR

The visual tree is responsible for:

Rendering visual elements

Propagate element opacity

Propagate Layout- and RenderTransforms

Propagate the IsEnabled property.

Do Hit-Testing

RelativeSource (FindAncestor)

Programmatically Find an Ancestor in the Visual Tree

If you are a child element of a user interface and you want to access data from a parent

element, but you don't know how many levels up that elemens is, it's the best solution to

navigate up the tree until it finds an element of the requested type.

This helper does excactly this. You can use almost the same code to navigate through the

logical tree.

public static class VisualTreeHelperExtensions

{

public static T FindAncestor<T>(DependencyObject dependencyObject)

where T : class

{

DependencyObject target = dependencyObject;

do

{

target = VisualTreeHelper.GetParent(target);

}

while (target != null && !(target is T));

return target as T;

}

}

The following example shows how to use the helper. It starts at this and navigates up the

visual tree until it finds an element of type Grid. If the helper reaches the root element of the

tree, it returns null.

var grid = VisualTreeHelperExtensions.FindAncestor<Grid>(this);

Dependency Properties

Introduction

Value resolution strategy

The magic behind it

How to create a DepdencyProperty

Readonly DependencyProperties

Attached DependencyProperties

Listen to dependency property changes

http://www.wpftutorial.net/DependencyProperties.html#changes

http://www.wpftutorial.net/DependencyProperties.html#attached

http://www.wpftutorial.net/DependencyProperties.html#readonly

http://www.wpftutorial.net/DependencyProperties.html#creation

http://www.wpftutorial.net/DependencyProperties.html#howitworks

http://www.wpftutorial.net/DependencyProperties.html#valueres

http://www.wpftutorial.net/DependencyProperties.html#introduction

http://www.google.com/search?q=is+msdn.microsoft.com

How to clear a local value

Introduction

When you begin to develop appliations with WPF, you will soon stumble across

DependencyProperties. They look quite similar to normal .NET properties, but the concept

behind is much more complex and powerful.

The main difference is, that the value of a normal .NET property is read directly from a

private member in your class, whereas the value of a DependencyProperty is resolved

dynamically when calling the GetValue() method that is inherited from DependencyObject.

When you set a value of a dependency property it is not stored in a field of your object,

but in a dictionary of keys and values provided by the base class DependencyObject. The

key of an entry is the name of the property and the value is the value you want to set.

The advantages of dependency properties are

Reduced memory footprint

It's a huge dissipation to store a field for each property when you think that over 90%

of the properties of a UI control typically stay at its initial values. Dependency

properties solve these problems by only store modified properties in the instance.

The default values are stored once within the dependency property.

Value inheritance

When you access a dependency property the value is resolved by using a value

resolution strategy. If no local value is set, the dependency property navigates up the

logical tree until it finds a value. When you set the FontSize on the root element it

applies to all textblocks below except you override the value.

Change notification

Dependency properties have a built-in change notification mechanism. By registering

a callback in the property metadata you get notified, when the value of the property

has been changed. This is also used by the databinding.

Value resolution strategy

Every time you access a dependency property, it internally resolves the value by following

the precedence from high to low. It checks if a local value is available, if not if a custom style

http://www.wpftutorial.net/DependencyProperties.html#clear

trigger is active,... and continues until it founds a value. At last the default value is always

available.

The magic behind it

Each WPF control registers a set of DependencyProperties to the static DependencyProperty

class. Each of them consists of a key - that must be unique per type - and a metadata that

contain callbacks and a default value.

All types that want to use DependencyProperties must derive from DependencyObject. This

baseclass defines a key, value dictionary that contains local values of dependency

properties. The key of an entry is the key defined with the dependency property.

When you access a dependency property over its .NET property wrapper, it internally calls

GetValue(DependencyProperty) to access the value. This method resolves the value by

using a value resolution strategy that is explained in detail below. If a local value is

available, it reads it directly from the dictionary. If no value is set if goes up the logical tree

and searches for an inherited value. If no value is found it takes the default value defined in

the property metadata. This sequence is a bit simplified, but it shows the main concept.

How to create a DependencyProperty

To create a DependencyProperty, add a static field of type DepdencyProperty to your type

and call DependencyProperty.Register() to create an instance of a dependency property.

The name of the DependendyProperty must always end with ...Property. This is a naming

convention in WPF.

To make it accessable as a normal .NET property you need to add a property wrapper. This

wrapper does nothing else than internally getting and setting the value by using the

GetValue() and SetValue() Methods inherited from DependencyObject and passing the

DependencyProperty as key.

Important: Do not add any logic to these properties, because they are only called

when you set the property from code. If you set the property from XAML the

SetValue() method is called directly.

If you are using Visual Studio, you can type propdp and hit 2x tab to create a dependency

property.

// Dependency Property

public static readonly DependencyProperty CurrentTimeProperty =

DependencyProperty.Register( "CurrentTime", typeof(DateTime),

typeof(MyClockControl), new FrameworkPropertyMetadata(DateTime.Now));

// .NET Property wrapper

public DateTime CurrentTime

{

get { return (DateTime)GetValue(CurrentTimeProperty); }

set { SetValue(CurrentTimeProperty, value); }

}

Each DependencyProperty provides callbacks for change notification, value coercion and

validation. These callbacks are registered on the dependency property.

new FrameworkPropertyMetadata( DateTime.Now,

OnCurrentTimePropertyChanged,

OnCoerceCurrentTimeProperty ),

OnValidateCurrentTimeProperty );

Value Changed Callback

The change notification callback is a static method, that is called everytime when the value

of the TimeProperty changes. The new value is passed in the EventArgs, the object on which

the value changed is passed as the source.

private static void OnCurrentTimePropertyChanged(DependencyObject source,

DependencyPropertyChangedEventArgs e)

{

MyClockControl control = source as MyClockControl;

DateTime time = (DateTime)e.NewValue;

// Put some update logic here...

}

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Coerce Value Callback

The coerce callback allows you to adjust the value if its outside the boundaries without

throwing an exception. A good example is a progress bar with a Value set below the

Minimum or above the Maximum. In this case we can coerce the value within the allowed

boundaries. In the following example we limit the time to be in the past.

private static object OnCoerceTimeProperty( DependencyObject sender, object data )

{

if ((DateTime)data > DateTime.Now )

{

data = DateTime.Now;

}

return data;

}

Validation Callback

In the validate callback you check if the set value is valid. If you return false, an

ArgumentException will be thrown. In our example demand, that the data is an instance of a

DateTime.

private static bool OnValidateTimeProperty(object data)

{

return data is DateTime;

}

Readonly DependencyProperties

Some dependency property of WPF controls are readonly. They are often used to report the

state of a control, like the IsMouseOver property. Is does not make sense to provide a setter

for this value.

Maybe you ask yourself, why not just use a normal .NET property? One important reason is

that you cannot set triggers on normal .NET propeties.

Creating a read only property is similar to creating a regular DependencyProperty. Instead of

calling DependencyProperty.Register() you call DependencyProperty.RegisterReadonly().

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This returns you a DependencyPropertyKey. This key should be stored in a private or

protected static readonly field of your class. The key gives you access to set the value from

within your class and use it like a normal dependency property.

Second thing to do is registering a public dependency property that is assigned to

DependencyPropertyKey.DependencyProperty. This property is the readonly property that

can be accessed from external.

// Register the private key to set the value

private static readonly DependencyPropertyKey IsMouseOverPropertyKey =

DependencyProperty.RegisterReadOnly("IsMouseOver",

typeof(bool), typeof(MyClass),

new FrameworkPropertyMetadata(false));

// Register the public property to get the value

public static readonly DependencyProperty IsMouseoverProperty =

IsMouseOverPropertyKey.DependencyProperty;

// .NET Property wrapper

public int IsMouseOver

{

get { return (bool)GetValue(IsMouseoverProperty); }

private set { SetValue(IsMouseOverPropertyKey, value); }

}

Attached Properties

Attached properties are a special kind of DependencyProperties. They allow you to attach a

value to an object that does not know anything about this value.

A good example for this concept are layout panels. Each layout panel needs different data to

align its child elements. The Canvas needs Top and Left, The DockPanel needs Dock, etc.

Since you can write your own layout panel, the list is infinite. So you see, it's not possible to

have all those properties on all WPF controls.




The solution are attached properties. They are defined by the control that needs the data

from another control in a specific context. For example an element that is aligned by a

parent layout panel.

To set the value of an attached property, add an attribute in XAML with a prefix of the

element that provides the attached property. To set the the Canvas.Top and Canvas.Left

property of a button aligned within a Canvas panel, you write it like this:

<Canvas>

<Button Canvas.Top="20" Canvas.Left="20" Content="Click me!"/>

</Canvas>

public static readonly DependencyProperty TopProperty =

DependencyProperty.RegisterAttached("Top",

typeof(double), typeof(Canvas),

new FrameworkPropertyMetadata(0d,

FrameworkPropertyMetadataOptions.Inherits));

public static void SetTop(UIElement element, double value)

{

element.SetValue(TopProperty, value);

}

public static double GetTop(UIElement element)

{

return (double)element.GetValue(TopProperty);

}

Listen to dependency property changes

If you want to listen to changes of a dependency property, you can subclass the type that

defines the property and override the property metadata and pass an

PropertyChangedCallback. But an much easier way is to get the

DependencyPropertyDescriptor and hookup a callback by calling AddValueChanged()

DependencyPropertyDescriptor textDescr = DependencyPropertyDescriptor.

FromProperty(TextBox.TextProperty, typeof(TextBox));





if (textDescr!= null)

{

textDescr.AddValueChanged(myTextBox, delegate

{

// Add your propery changed logic here...

});

}

How to clear a local value

Because null is also a valid local value, there is the constant

DependencyProperty.UnsetValue that describes an unset value.

button1.ClearValue( Button.ContentProperty );

Routed Events

Routed events are events which navigate up or down the visual tree acording to their

RoutingStrategy. The routing strategy can be bubble, tunnel or direct. You can hook up

event handlers on the element that raises the event or also on other elements above or

below it by using the attached event syntax: Button.Click="Button_Click".

Routed events normally appear as pair. The first is a tunneling event called

PreviewMouseDown and the second is the bubbling called MouseDown. They don't stop

routing if the reach an event handler. To stop routing then you have to set e.Handled = true;

Tunneling The event is raised on the root element and navigates down to the visual

tree until it reaches the source element or until the tunneling is stopped by marking

the event as handeld. By naming convention it is called Preview... and appears before

corresponding bubbling event.

Bubbling The event is raised on the source element and navigates up to the visual

tree until it reaches the root element or until the bubbling is stopped by marking the

event as handled. The bubbling event is raised after the tunneling event.

Direct The event is raised on the source element and must be handled on the source

element itself. This behavior is the same as normal .NET events.

How to Create a Custom Routed Event

// Register the routed event

public static readonly RoutedEvent SelectedEvent =

EventManager.RegisterRoutedEvent( "Selected", RoutingStrategy.Bubble,

typeof(RoutedEventHandler), typeof(MyCustomControl));

// .NET wrapper

public event RoutedEventHandler Selected

{

add { AddHandler(SelectedEvent, value); }

remove { RemoveHandler(SelectedEvent, value); }

}

// Raise the routed event "selected"

RaiseEvent(new RoutedEventArgs(MyCustomControl.SelectedEvent));

Layout and Controls

Introduction to WPF Layout

Why layout is so important

Layout of controls is critical to an applications usability. Arranging controls based on fixed

pixel coordinates may work for an limited enviroment, but as soon as you want to use it on

different screen resolutions or with different font sizes it will fail. WPF provides a rich set

built-in layout panels that help you to avoid the common pitfalls.

These are the five most popular layout panels of WPF:

Grid Panel

Stack Panel

Dock Panel

Wrap Panel

Canvas Panel

Best Practices

Avoid fixed positions - use the Alignment properties in combination with Margin to

position elements in a panel

Avoid fixed sizes - set the Width and Height of elements to Auto whenever possible.

Don't abuse the canvas panel to layout elements. Use it only for vector graphics.

Use a StackPanel to layout buttons of a dialog

Use a GridPanel to layout a static data entry form. Create a Auto sized column for the

labels and a Star sized column for the TextBoxes.

Use an ItemControl with a grid panel in a DataTemplate to layout dynamic key value

lists. Use the SharedSize feature to synchronize the label widths.

Vertical and Horizontal Alignment

Use the VerticalAlignment and HorizontalAlignmant properties to dock the controls to one or

multiple sides of the panel. The following illustrations show how the sizing behaves with the

different combinations.

http://www.wpftutorial.net/SharedSize.html

http://www.wpftutorial.net/Canvas.html

http://www.wpftutorial.net/WrapPanel.html

http://www.wpftutorial.net/DockPanel.html

http://www.wpftutorial.net/StackPanel.html

http://www.wpftutorial.net/GridLayout.html

Margin and Padding

The Margin and Padding properties can be used to reserve some space around of within the

control.

The Margin is the extra space around the control.

The Padding is extra space inside the control.

The Padding of an outer control is the Margin of an inner control.

Height and Width

Alltough its not a recommended way, all controls provide a Height and Width property to

give an element a fixed size. A better way is to use the MinHeight, MaxHeight, MinWidth and

MaxWidth properties to define a acceptable range.

If you set the width or height to Auto the control sizes itself to the size of the content.

Overflow Handling

Clipping

Layout panels typically clip those parts of child elements that overlap the border of the

panel. This behavior can be controlled by setting the ClipToBounds property to true or false.

Scrolling

When the content is too big to fit the available size, you can wrap it into a ScrollViewer. The

ScrollViewer uses two scroll bars to choose the visible area.

The visibility of the scrollbars can be controlled by the vertical and horizontal

ScrollbarVisibility properties.

<ScrollViewer>

<StackPanel>

<Button Content="First Item" />

<Button Content="Second Item" />

<Button Content="Third Item" />

</StackPanel>

</ScrollViewer>

Grid Panel

Introduction

The grid is a layout panel that arranges its child controls in a tabular structure of rows and

columns. Its functionality is similar to the HTML table but more flexible. A cell can contain

multiple controls, they can span over multiple cells and even overlap themselves.

The resize behaviour of the controls is defined by the HorizontalAlignment and

VerticalAlignment properties who define the anchors. The distance between the anchor and

the grid line is specified by the margin of the control

Define Rows and Columns

The grid has one row and column by default. To create additional rows and columns, you

have to add RowDefinition items to the RowDefinitions collection and ColumnDefinition

items to the ColumnDefinitions collection. The following example shows a grid with three

rows and two columns.

The size can be specified as an absolute amount of logical units, as a percentage value or

automatically.

Fixed Fixed size of logical units (1/96 inch)

Auto Takes as much space as needed by the contained control

Star (*) Takes as much space as available, percentally divided over all star-

sized columns. Star-sizes are like percentages, except that the sum of

all star columns does not have to be 100%. Remember that star-sizing

does not work if the grid size is calculated based on its content.

<Grid>

<Grid.RowDefinitions>

<RowDefinition Height="Auto" />


<RowDefinition Height="*" />

<RowDefinition Height="28" />

</Grid.RowDefinitions>

<Grid.ColumnDefinitions>

<ColumnDefinition Width="Auto" />

<ColumnDefinition Width="200" />

</Grid.ColumnDefinitions>

</Grid>

How to add controls to the grid

To add controls to the grid layout panel just put the declaration between the opening and

closing tags of the Grid. Keep in mind that the row- and columndefinitions must precced any

definition of child controls.

The grid layout panel provides the two attached properties Grid.Column and Grid.Row to

define the location of the control.

<Grid>

<Grid.RowDefinitions>



<RowDefinition Height="*" />

<RowDefinition Height="28" />

</Grid.RowDefinitions>


<ColumnDefinition Width="Auto" />

<ColumnDefinition Width="200" />


<Label Grid.Row="0" Grid.Column="0" Content="Name:"/>

<Label Grid.Row="1" Grid.Column="0" Content="E-Mail:"/>

<Label Grid.Row="2" Grid.Column="0" Content="Comment:"/>

<TextBox Grid.Column="1" Grid.Row="0" Margin="3" />



<Button Grid.Column="1" Grid.Row="3" HorizontalAlignment="Right"

MinWidth="80" Margin="3" Content="Send" />

</Grid>

Resizable columns or rows

WPF provides a control called the GridSplitter. This control is added like any other control to

a cell of the grid. The special thing is that is grabs itself the nearest gridline to change its

width or height when you drag this control around.

<Grid>


<ColumnDefinition Width="*"/>

<ColumnDefinition Width="Auto"/>



<Label Content="Left" Grid.Column="0" />

<GridSplitter HorizontalAlignment="Right"

VerticalAlignment="Stretch"

Grid.Column="1" ResizeBehavior="PreviousAndNext"

Width="5" Background="#FFBCBCBC"/>

<Label Content="Right" Grid.Column="2" />

</Grid>

The best way to align a grid splitter is to place it in its own auto-sized column. Doing it this

way prevents overlapping to adjacent cells. To ensure that the grid splitter changes the size

of the previous and next cell you have to set the ResizeBehavior to PreviousAndNext.

The splitter normally recognizes the resize direction according to the ratio between its

height and width. But if you like you can also manually set the ResizeDirection to Columns or

Rows.

<GridSplitter ResizeDirection="Columns"/>

How to share the width of a column over multiple grids

The shared size feature of the grid layout allows it to synchronize the width of columns over

multiple grids. The feature is very useful if you want to realize a multi-column listview by

using a grid as layout panel within the data template. Because each item contains its own

grid, the columns will not have the same width.

By setting the attached property Grid.IsSharedSizeScope to true on a parent element you

define a scope within the column-widths are shared.

To synchronize the width of two columndefinitions, set the SharedSizeGroup to the same

name.

<ItemsControl Grid.IsSharedSizeScope="True" >

<ItemsControl.ItemTemplate>

<DataTemplate>

<Grid>


<ColumnDefinition SharedSizeGroup="FirstColumn" Width="Auto"/>



<TextBlock Text="{Binding Path=Key}" TextWrapping="Wrap"/>

<TextBlock Text="{Binding Path=Value}" Grid.Column="1" TextWrapping="Wrap"/>

</Grid>

</DataTemplate>

</ItemsControl.ItemTemplate>

</ItemsControl>

Useful Hints

Columns and rows that participate in size-sharing do not respect Star sizing. In the size-

sharing scenario, Star sizing is treated as Auto. Since TextWrapping on TextBlocks within an

SharedSize column does not work you can exclude your last column from the shared size.

This often helps to resolve the problem.

Using GridLenghts from code

If you want to add columns or rows by code, you can use the GridLength class to define the

differenz types of sizes.

Auto sized GridLength.Auto

Star sized new GridLength(1,GridUnitType.Star)

Fixed size new GridLength(100,GridUnitType.Pixel)

Grid grid = new Grid();

ColumnDefinition col1 = new ColumnDefinition();

col1.Width = GridLength.Auto;

ColumnDefinition col2 = new ColumnDefinition();

col2.Width = new GridLength(1,GridUnitType.Star);

grid.ColumnDefinitions.Add(col1);

grid.ColumnDefinitions.Add(col2);

WPF StackPanel

Introduction

The StackPanel in WPF is a simple and useful layout panel. It stacks its child elements below

or beside each other, dependening on its orientation. This is very useful to create any kinds

of lists. All WPF ItemsControls like ComboBox, ListBox or Menu use a StackPanel as their

internal layout panel.





<StackPanel>

<TextBlock Margin="10" FontSize="20">How do you like your coffee?</TextBlock>

<Button Margin="10">Black</Button>

<Button Margin="10">With milk</Button>

<Button Margin="10">Latte machiato</Button>

<Button Margin="10">Chappuchino</Button>

</StackPanel>

Stack Items horizontally

A good example for a horizontal stack panel are the "OK" and "Cancel" buttons of a dialog

window. Because the size of the text can change if the user changes the font-size or

switches the language we should avoid fixed sized buttons. The stack panel aligns the two

buttons depending on their desired size. If they need more space they will get it

automatically. Never mess again with too small or too large buttons.

<StackPanel Margin="8" Orientation="Horizontal">

<Button MinWidth="93">OK</Button>

<Button MinWidth="93" Margin="10,0,0,0">Cancel</Button>

</StackPanel>

Built-in Controls of WPF

The WPF framework provides a rich set of built-in controls. The controls can be devided in

the following categories.

Third Party Controls

DataGrid

ItemsControl

LivePreview

ComboBox

Dialogs

Slider

Popup

RadioButton

ToolTips

TextBox

Menus

Expander

PasswordBox

ContextMenu

Calendar

ListBox

ListView

Window

DataBinding in WPF

Introduction

WPF provides a simple and powerful way to auto-update data between the business model

and the user interface. This mechanism is called DataBinding. Everytime when the data of

your business model changes, it automatically reflects the updates to the user interface and

vice versa. This is the preferred method in WPF to bring data to the user interface.

Databinding can be unidirectional (source -> target or target <- source), or bidirectional

(source <-> target).

The source of a databinding can be a normal .NET property or a DependencyProperty. The

target property of the binding must be a DependencyProperty.

To make the databinding properly work, both sides of a binding must provide a change

notification that tells the binding when to update the target value. On normal .NET

properties this is done by raising the PropertyChanged event of the

INotifyPropertyChanged interface. On DependencyProperties it is done by the

PropertyChanged callback of the property metadata

Databinding is typically done in XAML by using the {Binding} markup extension. The

following example shows a simple binding between the text of a TextBox and a Label that

reflects the typed value:

<StackPanel>

<TextBox x:Name="txtInput" />

<Label Content="{Binding Text, ElementName=txtInput,

UpdateSourceTrigger=PropertyChanged}" />

</StackPanel>

DataContext

Every WPF control derived from FrameworkElement has a DataContext property. This

property is meant to be set to the data object it visualizes. If you don't explicity define a

source of a binding, it takes the data context by default.

The DataContext property inherits its value to child elements. So you can set the

DataContext on a superior layout container and its value is inherited to all child elements.

This is very useful if you want to build a form that is bound to multiple properties of the

same data object.

<StackPanel DataContext="{StaticResource myCustomer}">

<TextBox Text="{Binding FirstName}"/>

<TextBox Text="{Binding LastName}"/>

<TextBox Text="{Binding Street}"/>

<TextBox Text="{Binding City}"/>

</StackPanel>

ValueConverters

If you want to bind two properties of different types together, you need to use a

ValueConverter. A ValueConverter converts the value from a source type to a target type

and back. WPF already includes some value converters but in most cases you will need to

write your own by implementing the IValueConverter interface.

A typical example is to bind a boolean member to the Visibility property. Since the visibility

is an enum value that can be Visible, Collapsed or Hidden, you need a value converter.

<StackPanel>

<StackPanel.Resources>

<BooleanToVisibilityConverter x:Key="boolToVis" />

</StackPanel.Resources>

<CheckBox x:Name="chkShowDetails" Content="Show Details" />

<StackPanel x:Name="detailsPanel"

Visibility="{Binding IsChecked, ElementName=chkShowDetails,

Converter={StaticResource boolToVis}}">

</StackPanel>

</StackPanel>

The following example shows a simple converter that converts a boolen to a visibility

property. Note that such a converter is already part of the .NET framework.

public class BooleanToVisibilityConverter : IValueConverter

{

public object Convert(object value, Type targetType, object parameter,

CultureInfo culture)

{

if (value is Boolean)

{

return ((bool)value) ? Visibility.Visible : Visibility.Collapsed;

}

return value;

}

public object ConvertBack(object value, Type targetType, object parameter,


{

throw new NotImplementedException();

}

}

Tip: you can derive your value converter from MarkupExtension and return its own instance

in the ProvideValue override. So you can use it directly without referencing it from the

resources.

How to Navigate, Group, Sort and Filter Data in WPF

What is a CollectionView?

Navigation

Filtering

Sorting

Grouping

How to create a CollectionView in XAML

What is a CollectionView?

WPF has a powerful data binding infrastructure. It allows you to bind almost any kind of

collection directly to a view. But when it comes to sorting, filtering and grouping the support

of the collections is rare. That's the point where the CollectionView comes into play. A

collection view is a wrapper around a collection that provides the following additional

features:

Navigation

Sorting

Filtering

Grouping

http://www.wpftutorial.net/DataViews.html#xaml

http://www.wpftutorial.net/DataViews.html#grouping

http://www.wpftutorial.net/DataViews.html#sorting

http://www.wpftutorial.net/DataViews.html#filtering

http://www.wpftutorial.net/DataViews.html#navig

http://www.wpftutorial.net/DataViews.html#intro

How to Create and Use a CollectionView

The following example shows you how to create a collection view and bind it to a ListBox

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

<ListBox ItemsSource={Binding Customers} />

</Window>

public class CustomerView

{

public CustomerView()

{

DataContext = new CustomerViewModel();

}

}

public class CustomerViewModel

{

private ICollectionView _customerView;

public ICollectionView Customers

{

get { return _customerView; }

}

public CustomerViewModel()

{

IList<Customer> customers = GetCustomers();

_customerView = CollectionViewSource.GetDefaultView(customers);

}

}

Navigation


The collection view adds support for selection tracking. If you set the property

IsSynchronizedWithCurrentItem to True on the view that the collection is bound to, it

automatically synchronizes the current item of the CollectionView and the View.

<ListBox ItemsSource="{Binding Customers}" IsSynchronizedWithCurrentItem="True" />

If you are using a MVVM (Model-View-ViewModel) pattern, you don't have to extra wire-up

the SelectedItem of the control, because it's implicity available over the CollectionView.

IList<Customer> customers = GetCustomers();

ICollectionView _customerView = CollectionViewSource.GetDefaultView(customers);

_customerView.CurrentChanged = CustomerSelectionChanged;

private CustomerSelectionChanged(object sender, EventArgs e)

{

// React to the changed selection

}

You can also manually control the selection from the ViewModel by calling the

MoveCurrentToFirst() or MoveCurrentToLast() methods on the CollectionView.

Filtering

To filter a collection view you can define a callback method that determines if the item

should be part of the view or not. That method should have the following signature: bool

Filter(object item). Now set the delegate of that method to the Filter property of the

CollectionView and you're done.


_customerView.Filter = CustomerFilter

private bool CustomerFilter(object item)

{

Customer customer = item as Customer;

return customer.Name.Contains( _filterString );

}

Refresh the filter

If you change the filter criteria and you want to refresh the view, you have to call Refresh()

on the collection view

public string FilterString

{

get { return _filterString; }

set

{

_filterString = value;

NotifyPropertyChanged("FilterString");

_customerView.Refresh();

}

}

Sorting

Sorting data ascending or descending by one or multiple criterias is a common requirement

for viewing data. The collection view makes it so easy to achieve this goal. Just add as many

SortDescriptions as you like to the CollectionView


_customerView.SortDescriptions.Add(

new SortDescription("LastName", ListSortDirection.Ascending );

_customerView.SortDescriptions.Add(

new SortDescription("FirstName", ListSortDirection.Ascending );

Fast Sorting

The sorting technique explained above is really simple, but also quite slow for a large

amount of data, because it internally uses reflection. But there is an alternative, more

performant way to do sorting by providing a custom sorter.



ListCollectionView _customerView = CollectionViewSource.GetDefaultView(customers);

as ListCollectionView;

_customerView.CustomSort = new CustomerSorter();

public class CustomerSorter : IComparer

{

public int Compare(object x, object y)

{

Customer custX = x as Customer;

Customer custY = y as Customer;

return custX.Name.CompareTo(custY.Name);

}

}

Grouping

Grouping is another powerful feature of the CollectionView. You can define as many groups

as you like by adding GroupDescriptions to the collection view.

Note: Grouping disables virtualization! This can bring huge performance issues on large

data sets. So be careful when using it.


_customerView.GroupDescriptions.Add(new PropertyGroupDescription("Country"));

To make the grouping visible in the view you have to define a special GroupStyle on the

view.

<ListBox ItemsSource="{Binding Customers}">

<ListBox.GroupStyle>

<GroupStyle.HeaderTemplate>

<DataTemplate>

<TextBlock Text="{Binding Path=Name}"/>

</DataTemplate>

</GroupStyle.HeaderTemplate>



</ListBox.GroupStyle>

</ListBox>

How to create a CollectionView in XAML

It's also possible to create a CollectionView completely in XAML

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

<Window.Resources>

<CollectionViewSource Source="{Binding}" x:Key="customerView">

<CollectionViewSource.GroupDescriptions>

<PropertyGroupDescription PropertyName="Country" />

</CollectionViewSource.GroupDescriptions>

</CollectionViewSource>

</Window.Resources>

<ListBox ItemSource="{Binding Source={StaticResource customerView}}" />

</Window>

Model-View-ViewModel Pattern

This article is not yet finished...

Introduction

In conventional user interface programming techniques (as we know it from WinForms) we

usually add event handlers to controls and implement the logic of a view in the code-behind.

It is the most simple and fastest way to get a functional user interface. But this approach

has some disadvantages:

Presentation and logic are tightly coupled

Replacing a control on the view often requires code changes

You cannot have more than one view sharing the same logic

To test the user interface logic you need to do complex UI testing.

Introducing the Model-View-ViewModel pattern

WPF brings up a very flexible and powerful databinding framework and this favors a new

pattern how to bind presentation and logic together.

The idea of the MVVM pattern is the following:

A model that contains the data

A passive view-model that collects and prepares the data so that is can easy be

consumed by the view.

And a view that is defined in XAML and should not have any logic in the code-behind.

It binds to the view-model by only using data binding.

Model-View-ViewModel Example

Model

ViewModel

View

Data Validation in WPF

What we want to do is a simple entry form for an e-mail address. If the user enters an invalid

e-mail address, the border of the textbox gets red and the tooltip is showing the reason.

Implementing a ValidationRule (.NET 3.0 style)

In this example I am implementing an generic validation rule that takes a regular expression

as validation rule. If the expression matches the data is treated as valid.

/// <summary>

/// Validates a text against a regular expression

/// </summary>

public class RegexValidationRule : ValidationRule

{

private string _pattern;

private Regex _regex;

public string Pattern

{

get { return _pattern; }

set

{

_pattern = value;

_regex = new Regex(_pattern, RegexOptions.IgnoreCase);

}

}

public RegexValidationRule()

{

}

public override ValidationResult Validate(object value, CultureInfo ultureInfo)

{

if (value == null || !_regex.Match(value.ToString()).Success)

{

return new ValidationResult(false, "The value is not a valid e-mail address");

}

else

{

return new ValidationResult(true, null);

}

}

}

First thing I need to do is place a regular expression pattern as string to the windows

resources

<Window.Resources>

<sys:String x:Key="emailRegex">^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@

[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]

*[a-zA-Z]$</sys:String>

</Window.Resources>

Build a converter to convert ValidationErrors to a multi-line string

The following converter combines a list of ValidationErrors into a string. This makes the

binding much easier. In many samples on the web you see the following binding expression:

{Binding RelativeSource={RelativeSource Self},Path=(Validation.Errors)[0].ErrorContent}

This expression works if there is one validation error. But if you don't have any validation

errors the data binding fails. This slows down your application and causes the following

message in your debug window:

System.Windows.Data Error: 16 : Cannot get ‘Item[]‘ value (type ‘ValidationError’) from

‘(Validation.Errors)’ (type ‘ReadOnlyObservableCollection`1′). BindingExpression:Path=(0).

[0].ErrorContent; DataItem=’TextBox’...

The converter is both, a value converter and a markup extension. This allows you to create

and use it at the same time.

[ValueConversion(typeof(ReadOnlyObservableCollection<ValidationError>),

typeof(string))]

public class ValidationErrorsToStringConverter : MarkupExtension, IValueConverter

{

public override object ProvideValue(IServiceProvider serviceProvider)

{

return new ValidationErrorsToStringConverter();

}



{

ReadOnlyObservableCollection<ValidationError> errors =

value as ReadOnlyObservableCollection<ValidationError>;

if (errors == null)

{

return string.Empty;

}

return string.Join("\n", (from e in errors

select e.ErrorContent as string).ToArray());

}



{

throw new NotImplementedException();

}

}

Create an ErrorTemplate for the TextBox

Next thing is to create an error template for the text box.

<ControlTemplate x:Key="TextBoxErrorTemplate" TargetType="Control">

<Grid ClipToBounds="False" >

<Image HorizontalAlignment="Right" VerticalAlignment="Top"

Width="16" Height="16" Margin="0,-8,-8,0"

Source="{StaticResource ErrorImage}"

ToolTip="{Binding ElementName=adornedElement,

Path=AdornedElement.(Validation.Errors),

Converter={k:ValidationErrorsToStringConverter}}"/>

<Border BorderBrush="Red" BorderThickness="1" Margin="-1">

<AdornedElementPlaceholder Name="adornedElement" />

</Border>

</Grid>

</ControlTemplate>

The ValidationRule and the ErrorTemplate in Action

Finally we can add the validation rule to our binding expression that binds the Text property

of a textbox to a EMail property of our business object.

<TextBox x:Name="txtEMail" Template={StaticResource TextBoxErrorTemplate}>

<TextBox.Text>

<Binding Path="EMail" UpdateSourceTrigger="PropertyChanged" >

<Binding.ValidationRules>

<local:RegexValidationRule Pattern="{StaticResource emailRegex}"/>

</Binding.ValidationRules>

</Binding>

</TextBox.Text>

</TextBox>

How to manually force a Validation

If you want to force a data validation you can manually call UpdateSource() on the binding

expression. A useful scenario could be to validate on LostFocus() even when the value is

empty or to initially mark all required fields. In this case you cann call ForceValidation() in

the Loaded event of the window. That is the time, when the databinding is established.

The following code shows how to get the binding expression from a property of a control.

private void ForceValidation()

{

txtName.GetBindingExpression(TextBox.TextProperty).UpdateSource();

}

ValueConverters

Introduction

If you want to databind two properties that have incompatible types, you need a piece of

code in between, that converts the value from source to target type and back. This piece of

code is called ValueConverter. A value converter is a class, that implements the simple

interface IValueConverter with the two methods object Convert(object value) and object

ConvertBack(object value).

How to implement a ValueConverter

WPF already provides a few value converts, but you will soon need to implement your own

converts. To do this, add a class to your project and call it

[SourceType]To[TargetType]Converter. This is a common naming for value converters. Make

it public and implement the IValueConverter interface. That's all you need to do.

public class BoolToVisibilityConverter : IValueConverter

{

public object Convert(object value, Type targetType,

object parameter, CultureInfo culture)

{

// Do the conversion from bool to visibility

}

public object ConvertBack(object value, Type targetType,

object parameter, CultureInfo culture)

{

// Do the conversion from visibility to bool

}

}

How to use a ValueConverter in XAML

First thing you need to do is to map the namespace of your converter to a XAML namespace.

Then you can create an instance of a value converter in the resources of the view and give it

a name. Then you can reference it by using {StaticResource}

<Window x:Class="VirtualControlDemo.Window1"

...

xmlns:l="clr-namespace:VirtualControlDemo"

...>

<Window.Resources>

<l:BoolToVisibilityConverter x:Key="converter" />

</Window.Resources>

<Grid>

<Button Visibility="{Binding HasFunction,

Converter={StaticResource converter}}" />

</Grid>

</Window>

Simplify the usage of ValueConvers

If you want to use a normal ValueConverter in XAML, you have to add an instance of it to the

resources and reference it by using a key. This is cumbersome, because and the key is

typically just the name of the converter.

A simple and cool trick is to derive value converters from MarkupExtension. This way you

can create and use it in the binding like this: Text={Binding Time,

Converter={x:MyConverter}}, and that is quite cool!

public abstract class BaseConverter : MarkupExtension

{

public override object ProvideValue(IServiceProvider serviceProvider)

{

return this;

}

}

StringFormat Converter

The StringFormatConverter is a useful converter to control the format of an implicit string

conversion of an object (e.g. if you bind a DateTime to a TextBlock ).

[ValueConversion(typeof(object), typeof(string))]

public class StringFormatConverter : BaseConverter, IValueConverter

{


System.Globalization.CultureInfo culture)

{

string format = parameter as string;

if (!string.IsNullOrEmpty(format))

{

return string.Format(culture, format, value);

}

else

{

return value.ToString();

}


System.Globalization.CultureInfo culture)

{

return null;

}

}

Behaviors

A simple Border can be dragged by mouse - because of an attached drag behavior.

Introduction

Behaviors are a new concept, introduced with Expression Blend in Version 3, to

encapsulate pieces of functionality into a reusable component. These components

than can be attached to controls to give them an additional behavior.

The ideas behind behaviors are to give the interaction designer more flexibility to design

complex user interactions without writing any code.

Example of a behaviors are drag&drop, input validation, pan and zoom, re-position of

elements, etc... The list of possible behaviors is very long.

Imaging an application that has a list of customers and the user can add some of them to

subscriber lists. This interaction can be designed by providing an "Add" button next to each

subscriber list. But if the interaction designer wants to add drag&drop functionality, he

needs to discuss it with the developer and wait until the implementation is done. With

behaviors he just drags a drag and drop behavior on each list and we are done.

How to use behaviors in Expression Blend 3

Using behaviors in Expression Blend is as simple as adding an element to the design

surface. In the asset library you find a new secion called "Behaviors". It lists all behaviors

available within your project. Just grab one of these and drag it onto the element you want

to add this behavior and thats it.

The behavior appears as an child element in the visual tree. By clicking on it you can

configure the properties of the behavior.

How does it work

To add behaviors to an element you need some kind of an extension point. This is an

attached property called Interaction.Behaviors.

This attached property holds the list of behaviors for that element and pass a reference to

the element into the behavior. The behavior than can register itself to events and property

changes and so extend the functionality of the element.

The idea is simple, but very clever. They don't need any new infrastructure, they just reuse

the existing one.

<Border Background="LightBlue" >

<e:Interaction.Behaviors>

<b:DragBehavior/>

</e:Interaction.Behaviors>

<TextBlock Text="Drag me around!" />

</Border>

How to implement your own behavior

The following example shows the implementation of the drag behavior we used above. Just

derive from Behavior<T;gt; and override the OnAttached() method.

public class DragBehavior : Behavior<UIElement>

{

private Point elementStartPosition;

private Point mouseStartPosition;

private TranslateTransform transform = new TranslateTransform();

protected override void OnAttached()

{

Window parent = Application.Current.MainWindow;

AssociatedObject.RenderTransform = transform;

AssociatedObject.MouseLeftButtonDown += (sender, e) =>

{

elementStartPosition = AssociatedObject.TranslatePoint( new Point(), parent );

mouseStartPosition = e.GetPosition(parent);

AssociatedObject.CaptureMouse();

};

AssociatedObject.MouseLeftButtonUp += (sender, e) =>

{

AssociatedObject.ReleaseMouseCapture();

};

AssociatedObject.MouseMove += (sender, e) =>

{

Vector diff = e.GetPosition( parent ) - mouseStartPosition;

if (AssociatedObject.IsMouseCaptured)

{

transform.X = diff.X;

transform.Y = diff.Y;

}

};

}

}

List of some popular behaviors

Since its so cool and easy to create your own pice of interactivity, I am sure that we will find

hunderts of behaviors available soon. I tried to make a list of some popular ones.

Zoom Behavior

Glass Behavior

Shake Behavior

Transparency Behavior

Introduction to Styles in WPF

Introduction

Imagine you want to create an application with a unique design. All your buttons should

have an orange background and an italic font. Doing this the conventional way means that

you have to set the Background and the FontStyle property on every single button.

<StackPanel Orientation="Horizontal" VerticalAlignment="Top">

<Button Background="Orange" FontStyle="Italic"

Padding="8,4" Margin="4">Styles</Button>


Padding="8,4" Margin="4">are</Button>


Padding="8,4" Margin="4">cool</Button>

</StackPanel>

This code is neither maintainable nor short and clear. The solution for this problem are

styles.

The concept of styles let you remove all properties values from the individual user interface

elements and combine them into a style. A style consists of a list of setters. If you apply this

style to an element it sets all properties with the specified values. The idea is quite similar to

Cascading Styles Sheets (CSS) that we know from web development.

To make the style accessible to your controls you need to add it to the resources. Any

control in WPF have a list of resources that is inherited to all controls beneath the visual

tree. That's the reason why we need to specify a x:Key="myStyle" property that defines a

unique resource identifier.

To apply the style to a control we set the Style property to our style. To get it from the

resources we use the {StaticResource [resourceKey]} markup extension.

<Window>

<Window.Resources>

<Style x:Key="myStyle" TargetType="Button">

<Setter Property="Background" Value="Orange" />

<Setter Property="FontStyle" Value="Italic" />

<Setter Property="Padding" Value="8,4" />

<Setter Property="Margin" Value="4" />

</Style>

</Window.Resources>

<StackPanel Orientation="Horizontal" VerticalAlignment="Top">

<Button Style="{StaticResource myStyle}">Styles</Button>

<Button Style="{StaticResource myStyle}">are</Button>

<Button Style="{StaticResource myStyle}">cool</Button>

</StackPanel>

</Window>

What we have achieved now is

A maintainable code base

Removed the redundancy

Change the appearance of a set of controls from a single point

Possibility to swap the styles at runtime.

Style inheritance

A style in WPF can base on another style. This allows you to specify a base style that sets

common properties and derive from it for specialized controls.

<Style x:Key="baseStyle">

<Setter Property="FontSize" Value="12" />

<Setter Property="Background" Value="Orange" />

</Style>

<Style x:Key="boldStyle" BasedOn="{StaticResource baseStyle}">

<Setter Property="FontWeight" Value="Bold" />

</Style>

Control Templates

Introduction

Controls in WPF are separated into logic, that defines the states, events and properties and

template, that defines the visual appearance of the control. The wireup between the logic

and the template is done by DataBinding.

Each control has a default template. This gives the control a basic appearance. The default

template is typically shipped together with the control and available for all common windows

themes. It is by convention wrapped into a style, that is identified by value of the

DefaultStyleKey property that every control has.

The template is defined by a dependency property called Template. By setting this property

to another instance of a control template, you can completely replace the appearance

(visual tree) of a control.

The control template is often included in a style that contains other property settings. The

following code sample shows a simple control template for a button with an ellipse shape.

<Style x:Key="DialogButtonStyle" TargetType="Button">

<Setter Property="Template">

<Setter.Value>

<ControlTemplate TargetType="{x:Type Button}">

<Grid>

<Ellipse Fill="{TemplateBinding Background}"

Stroke="{TemplateBinding BorderBrush}"/>

<ContentPresenter HorizontalAlignment="Center"

VerticalAlignment="Center"/>

</Grid>

</ControlTemplate>

</Setter.Value>

</Setter>

</Style>

<Button Style="{StaticResource DialogButtonStyle}" />

A Button without and with a custom control template

ContentPresenter

When you create a custom control template and you want to define a placeholder that

renders the content, you can use the ContentPresenter. By default it adds the content of the

Content property to the visual tree of the template. To display the content of another

property you can set the ContentSource to the name of the property you like.

Triggers

{RelativeSource TemplatedParent} not working in DataTriggers of a

ControlTemplate

If you want to bind to a property of a property on your control like Data.IsLoaded you cannot

use a normal Trigger, since it does not support this notation, you have to use a DataTrigger.

But when you are using a DataTrigger, with {RelativeSource TemplatedParent} it will not

work. The reason is, that TemplatedParent can only be used within the

ControlTemplate. It is not working in the Trigger section. You have to use the

{RelativeSource Self} instead.

What if a Binding working or a Setter is not applied when using a control template

There is something you need to know when setting a value of an element within a control

template: The value does have a lower precendence as the local value! So if you are setting

the local value in the constructor of the contained element, you cannot override it within the

controltemplate. But if you use the element directly in your view, it will work. So be aware of

this behavior!.

Here you can find more information about DependencyProperty value precendence:

Dependency Property Value Precedence

Data Templates

Introduction

Data Template are a similar concept as Control Templates. They give you a very flexible and

powerful solution to replace the visual appearance of a data item in a control like

ListBox, ComboBox or ListView. In my opinion this is one of the key success factory of WPF.

If you don't specify a data template, WPF takes the default template that is just a TextBlock.

If you bind complex objects to the control, it just calls ToString() on it. Within a

DataTemplate, the DataContext is set the data object. So you can easily bind against the

data context to display various members of your data object

DataTemplates in Action: Building a simple PropertyGrid

Whereas it was really hard to display complex data in a ListBox with WinForms, its super

easy with WPF. The following example shows a ListBox with a list of DependencyPropertyInfo

instances bound to it. Without a DataTemplate you just see the result of calling ToString() on

the object. With the data template we see the name of the property and a TextBox that even

allows us to edit the value.

http://msdn.microsoft.com/en-us/library/ms743230.aspx

<ListBox ItemsSource="{Binding}" />



<ListBox ItemsSource="{Binding}" BorderBrush="Transparent"

Grid.IsSharedSizeScope="True"

HorizontalContentAlignment="Stretch">

<ListBox.ItemTemplate>

<DataTemplate>

<Grid Margin="4">


<ColumnDefinition Width="Auto" SharedSizeGroup="Key" />

<ColumnDefinition Width="*" />


<TextBlock Text="{Binding Name}" FontWeight="Bold" />

<TextBox Grid.Column="1" Text="{Binding Value }" />

</Grid>

</DataTemplate>

</ListBox.ItemTemplate>

</ListBox>

How to use a DataTemplateSelector to switch the Template depending on the

data

Our property grid looks nice so far, but it would be much more usable if we could switch the

editor depending on the type of the property.

The simplest way to do this is to use a DataTemplateSelector. The DataTemplateSelector

has a single method to override: SelectTemplate(object item, DependencyObject container).

In this method we decide on the provided item which DataTemplate to choose.

The following exmple shows an DataTemplateSelector that decides between tree data

templates:

public class PropertyDataTemplateSelector : DataTemplateSelector

{

public DataTemplate DefaultnDataTemplate { get; set; }

public DataTemplate BooleanDataTemplate { get; set; }

public DataTemplate EnumDataTemplate { get; set; }

public override DataTemplate SelectTemplate(object item,

DependencyObject container)

{

DependencyPropertyInfo dpi = item as DependencyPropertyInfo;

if (dpi.PropertyType == typeof(bool))

{

return BooleanDataTemplate;

}

if (dpi.PropertyType.IsEnum)

{

return EnumDataTemplate;

}

return DefaultnDataTemplate;

}

}

<Window x:Class="DataTemplates.Window1"

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

xmlns:l="clr-namespace:DataTemplates"

xmlns:sys="clr-namespace:System;assembly=mscorlib">

<Window.Resources>



<DataTemplate x:Key="DefaultDataTemplate">

...

</DataTemplate>



<DataTemplate x:Key="BooleanDataTemplate">

...

</DataTemplate>



<DataTemplate x:Key="EnumDataTemplate">

...

</DataTemplate>



<l:PropertyDataTemplateSelector x:Key="templateSelector"

DefaultnDataTemplate="{StaticResource DefaultDataTemplate}"

BooleanDataTemplate="{StaticResource BooleanDataTemplate}"

EnumDataTemplate="{StaticResource EnumDataTemplate}"/>

</Window.Resources>

<Grid>

<ListBox ItemsSource="{Binding}" Grid.IsSharedSizeScope="True"

HorizontalContentAlignment="Stretch"

ItemTemplateSelector="{StaticResource templateSelector}"/>

</Grid>

</Window>

How to react to IsSelected in the DataTemplate

If you want to change the appearance of a ListBoxItem when it is selected, you have to bind

the IsSelected property of the ListBoxItem. But this is a bit tricky, you have to use a relative

source with FindAcestor to navigate up the visual tree until you reach the ListBoxItem.

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