Programming Based on Events - Department of … · ¾Contrast ComboBox to ListBox objects by adding...

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Copyright © 2007Robinson College of Business, Georgia State UniversityDavid S. McDonald Director of Emerging TechnologiesTel: 404-413-7368; e-mail: [email protected]

9 Programming Based on Events9

David McDonald, Ph.D.Director of Emerging Technologies

C# Programming: From Problem Analysis to Program Design 2nd Edition

Chapter Objectives

Create applications that use the ListBox control object to enable multiple selections from a single j p gcontrolContrast ComboBox to ListBox objects by adding both types of controls to an application Add Menu and TabControl control options to Window forms and program their event-handler methodsWire multiple RadioButton and CheckBox object

C# Programming: From Problem Analysis to Program Design

Wire multiple RadioButton and CheckBox object events to a single event-handler method

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ListBox Control Objects

Displays list of items for single or multiple selections

√ Scroll bar is automatically added when total ynumber of items exceeds the number that can be displayed

Can add or remove items at design time or dynamically at run time

Includes number of properties and events


√ The Items property used to set initial values

• Click on (Collections) to add items

Adding a ListBox Control Object

Add ListBox control, then

click on Items


property (Collection) to

type entries

Figure 9-2 String Collection Editor

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ListBox Control Objects (continued)

Name property

√ Useful to set for program statements√ Useful to set for program statements

Sorted property

√ Set to true to avoid having to type values in sorted order

Register an event for the ListBox

√Might want to know when the item selection


√Might want to know when the item selection changes

√ Double-clicking on any control registers its default event for the control

√ SelectedIndexChanged: default event for ListBox


Register its event with the System.EventHandler delegateRegister its event with the System.EventHandler delegate

this.lstBoxEvents.SelectedIndexChanged += new System.EventHandler(this.listBox1_SelectedIndexChanged);

Visual Studio adds event-handler method

private void listBox1_SelectedIndexChanged

(object sender System EventArgs e)


(object sender, System.EventArgs e)

{

}

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To retrieve string data from ListBox use Text propertyText property

this.txtBoxResult.Text = this.lstBoxEvents.Text;

√Place in method body


√Place in method body

√When event fires, selection retrieved and stored in TextBox object



Figure 9-3 SelectedIndexChanged event fired

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Multiple Selections with a ListBoxSelectionMode Property has values of MultiSimple, MultiExtended, None, and One

√MultiSimple: use the spacebar and click the mouse√MultiSimple: use the spacebar and click the mouse

√MultiExtended can also use Ctrl key, Shift key, and arrow keys

foreach(string activity inlstBoxEvents.SelectedItems)

{


{

result += activity + " ";

}

this.txtBoxResult.Text = result;



Figure 9-4 Multiple selections within a ListBox object

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SelectedItem and SelectedItems return objects

√ Store numbers in the ListBox, once retrieved as objects, cast the object into an int or double for processing

Adding items to a ListBox at run time by using Add( ) method with the Items property

lstBoxEvents.Items.Add("string value to add");

private void btnNew_Click(object sender, System.EventArgs e)


p ( j , y g )

{

lstBoxEvents.Items.Add(txtBoxNewAct.Text);

}

ListBoxExample


Figure 9-5 Add( ) method executed inside the buttonClick event

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ListBox Control Properties


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ListBox Control Methods


ListBox Control Methods (continued)


Note that ListBox control inherits members from Control class

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ComboBox Controls

Extra TextBox object with ComboBox –User selects from list or types new value


Figure 9-6 ComboBox and ListBox objects

ComboBox Controls (continued)

Top line leftTop line left blank in ComboBox when DropDownStyle property is set to DropDown(default setting)


(default setting)

Figure 9-7 ComboBox list of choices

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Handling ComboBox Events

ComboBox only allows a single selection to be made

Default event-handler method: SelectedIndexChanged( )

√ Same as ListBox control object

Could register KeyPress( ) event-handler method


√ BUT, event is fired with each and EVERY keystroke

Programming Event HandlersSince ListBox object allows multiple selections, Text property cannot be used

√ Text ONLY gets the first one selected

Use the SelectedItems, SelectedIndices, or Items to retrieve a collection of items selected

√ Zero-based structures

√ Access them as you would access an element from


an array

√ SelectedIndices is a collection of indexes

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Programming Event Handlers

KeyPress( ) event-

handler method

fired with each


Figure 9-8 KeyPress and SelectedIndexChanged events fired

keystroke

MenuStrip Controls

Offers advantage of taking up minimal spaceDrag and drop MenuStrip object from toolbox to yourDrag and drop MenuStrip object from toolbox to your form√ Icon representing MenuStrip placed in Component

TraySelect MenuStrip object to set its propertiesTo add the text for a menu option, select the MenuStrip icon and then click in the upper left corner


MenuStrip icon and then click in the upper-left corner of the form

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MenuStrip Controls (continued)

Drag MenuStrip control to form,

then click here to display Menu

structure


Figure 9-9 First step to creating a menu

MenuStrip Control Objects Ampersand (&) is typed between the F and o for the Format option to make Alt+o shortcut for Formatfor Format


Figure 9-10 Creating a shortcut for a menu item

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MenuStrip Control Objects (continued)

To create separators, right-click on the text glabel (below the needed separator) Select Insert Separator


Figure 9-11 Adding a separator

MenuStrip Control Objects

Set the text to be displayedwhen the cursor is rested on top of the control


Figure 9-12 Setting the Property for the ToolTip control

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Wire Methods to Menu Option Event

Set the Name property for each menu option

√ Do this first, then wire the event

Click events are registered by double-clicking on the Menu option

When the menu option is clicked, the event triggers,


happens, or is fired

Adding Predefined Standard Windows Dialog Boxes

Included as part of .NETIncluded as part of .NET

Dialog boxes that look like standard Windows dialog boxes

√ File Open, File Save, File Print, and File Print Preview

√ Format Font


√ Format Font

√ Format Color dialogs

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Adding Predefined Standard Windows Dialog Boxes – Color

private void menuColor_Click(object sender, System EventArgs e)

Retrieves the System.EventArgs e)

{colorDialog1.Color = lblOutput.ForeColor;if (colorDialog1.ShowDialog( ) !=

DialogResult.Cancel ){

current ForeColor property setting

for the Label object

Checks to see if C l b


{lblOutput.ForeColor = colorDialog1.Color;

}}

Cancel button clicked

Set to selection

made

CheckBox ObjectsAppear as small boxes

√ Allow users to make a yes/no or true/false selectionselection

Checked property set to either true or false depending on whether a check mark appears or not

√ Default false value

CheckChanged( ) – default event-handler method


√ Fired when CheckBox object states change

Can wire one event handler to multiple objects

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Wiring One Event Handler to Multiple Objects

Using Properties window, click on the Events Icon Click the down arrow associated with that eventSelect method to handle the event


Select method to handle the eventFollow the same steps for other objects

CheckBox Object


Figure 9-17 ComputeCost_CheckedChanged( ) method raised

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GroupBox Objects

CheckBox objects may be grouped together for visual appearanceappearance

Can move or set properties that impact the entire group

A GroupBox control should be placed on the form before you add objects

GroupBox control adds functionality to RadioButton


p yobjects

√ Allow only one selection

RadioButton ObjectsAppear as small circles

Give users a choice between two or more options p

√ Not appropriate to select more than one CheckBox object with RadioButton objects

Group RadioButton objects by placing them on a Panel or GroupBox control

√


√ Setting the Text property for the GroupBox adds a labeled heading over the group

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RadioButton Objects (example)


Figure 9-18 GroupBox and RadioButton objects added

RadioButton Objects (continued)

Turn selection on

this.radInterm.Checked = true;

Raise a number of events, including Click( ) and CheckedChanged( ) events


Wire the event-handler methods for RadioButton objects, just like CheckBox

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RadioButton Objects (continued)Register ComputeCost_CheckedChanged( ) method( )


Figure 9-19 Wired Click event

RadioButton Objects (continued)ComputeCost_CheckedChanged( ) method

if (this.radBeginner.Checked){

cost +=10;this.lblMsg.Text =

"Beginner “ +


“-- Extra $10 charge";}else// more statements

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ComputeCost_CheckChanged( ) and Click( ) Events Raised


Figure 9-20 ComputeCost_CheckedChanged( ) and Click( ) events raised

TabControl Controls

Sometime an application requires too l f i lmany controls for a single screen

TabControl object displays multiple tabs, like dividers in a notebookEach separate tab can be clicked to display other options


p y pAdd a TabControl object to the page by dragging the control from the Containersection of the Toolbox

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TabControl Controls (continued)


Figure 9-21 Tabbed controlled application

TabControl Controls (continued)


Figure 9-22 TabControl object stretched to fill form

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TabControl Controls (continued)TabPage property enables

t f tyou to format individual tabs Clicking the ellipsis beside the Collection value displays the TabPage


the TabPage Collection Editor

Programming Based on Events - Department of … · ¾Contrast ComboBox to ListBox objects by adding...

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