11

ASP.NET Controls

Beginning ASP.NET 4.0 in C# 2010

Chapter 6

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Objectives

You will be able to Use basic ASP.NET controls to design

a web page. Process user inputs from ASP.NET

controls in server side C# code. Understand the relationship between

the ASP.NET code that you write in Visual Studio and the HTML that is received by the browser.

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ASP.NET Controls

Building blocks for a web page

Normal HTML HTML Server Controls ASP.NET Server Controls ASP.NET AJAX Controls User/Custom controls

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Normal HTML

Normal HTML Can be included in an ASPX.NET page. Passed to browser as written. Usually not processed by server code.

Server code can get user input values from normal HTML input controls.

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HTML Server Controls

Discussed in Chapter 5 of our textbook.

Normal HTML plus “runat=server” Permit server code to modify the HTML. Mainly to support backward

compatibility. Move existing HTML into an ASP.NET site.

Not used in this class.

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ASP.NET Server Controls

Pseudo-HTML

Include “asp:” prefix <asp:Label ... > text </asp:Label>

Translated into real HTML before being sent to browser.

WYSIWYG Designer in Visual Studio. Conveniently accessible to our server side code.

May result in JavaScript script being sent to the browser and exectuted there.

Used extensively in this course.

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ASP.NET AJAX Server Controls

Include Javascript code that runs on the browser. Permits more interactive user interface.

Ignore for now.

We will look at AJAX in some depth later in the course.

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User Controls and Custom Controls

Controls created by the developer i.e. by us!

Analogous to functions in software. Reusable bundles of code.

Covered lightly later in the course.

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Example

A simple web application using ASPX controls matching the HTML form seen earlier.

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Example

Permits user to enter personal information.

A typical real web app would write this information into a database.

We will use a Visual Studio breakpoint to look at the user inputs as properties of ASPX control objects.

Create a new empty web site called ASPX_Demo.

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New Web Site

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New Web Site in Visual Studio

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Empty Web Site

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Add New Page to the Website

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Set Name to Demo.aspx

Set file name.

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Initial File

Set Design View.

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Demo.aspx

View Toolbox.

Position cursor in div box.

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Design the Form

Add “Standard” (ASPX) controls from the Toolbox to the design surface to design a form similar to the one seen earlier. Double click to add at cursor position Or drag and drop.

Use space bar and new line to control position of elements.

Check the Source view from time to time as you lay out the form.

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Normal Flow

In the browser, controls normally appear on the page like text in a word processing program. Left to right Top to bottom

HTML position attributes can force exceptions to normal flow.

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Design the Form

Give each element a meaningful name. Except the labels.

To put radio buttons into the same group give them the same value for their GroupName property.

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Design the Form

To specify values for the Classification Dropdown List, click on Items in its Properties. Click on the ... icon for Items.

Use numeric values, 0 – 5, for “Value”.

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The Form

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Title is a Property of the Document

Select DOCUMENT

Set Title

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What We Wrote

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What we wrote

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File ASPX_Demo.aspx

This text file holds the results of our design work.

We could have written it with NotePad. The visual designer is just a more

convenient view of the file.

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Build and Run

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Demo.aspx in Chrome

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What the Browser Received

Every aspx page consists of exactly one HTML form.

The action attribute specifies the URL to request when the user clicks the Submit button.

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The TextBoxes

Each ASPX Label became an HTML span.

Each ASPX TextBox became an HTML input, type=“text”

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The Radio Buttons

Each asp:RadioButton became an HTML input, type=“radio”.

ASPX “ID” became “id” in HTML.

ASPX “GroupName” became “name” in HTML.

ASPX “Text” became text in an HTML label.

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Checkbox and Dropdown List

The asp:CheckBox became an HTML input, type = “checkbox”

The asp:DropDownList became an HTML select.

Each asp.ListItem became an HTML option.

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The Button

The asp:Button became an HTML input, type=“submit”.

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Postback

Clicking the Submit button will result in a postback.

Changing other inputs does not.

Users expect to be able to make changes to inputs before they click a button to submit them.

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Code to Access Inputs

We can write C# code to process inputs. The “code behind” file, Demo.aspx.cs

Double click on Demo.aspx.cs in the Solution Explorer.

Visual Studio opens the file in an editor window.

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Demo.aspx.cs

Can be deleted.

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Inputs

Input from each control is available as a property of a C# object corresponding to the control.

Object name is the name that we gave the control in the ASPX page.

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Code to Access Inputs

using System;

public partial class _Default : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

if (IsPostBack)

{

String Last_Name = tbLastName.Text;

String First_Name = tbFirstName.Text;

Boolean Unspecified = rbUnspecified.Checked;

Boolean Male = rbMale.Checked;

Boolean Female = rbFemale.Checked;

Boolean CSE_Dept_Major = cbCseMajor.Checked;

String Classification = ddlClassification.SelectedValue;

}

}

}

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Looking at Input Values

Set breakpoint at the end of the “if” block and examine the variables. Hover the mouse over a variable.

Or rightclick and select QuickWatch.

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Inputs Filled In

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Stopped at Breakpoint

Right click on a variable and select QuickWatch.

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QuickWatch

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QuickWatch

Or just hover the cursor over a variable and see its value in a tooltip.

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Looking at Input Values

Where do these values come from?

When a postback is done, the server (IIS) instantiates objects corresponding to our ASPX controls. Initializes properties with values received

from the browser.

Our event handler code can refer to the control objects by name and access their properties.

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Looking at Input Values

The only data available to the server is that provided by the user in the HTML <form> input elements.

Name-Value pairs are included in the request by the browser.

Appended to the URL for “get” Included in the request Message for “post”

What do .aspx pages do (get or post)? How can we tell?

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What the Browser Received

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Looking at Input Values

The entire collection of name-value pairs is directly available to our code as the Form property of the Request object. Set up by IIS when it processes a page

request. Would include values from plain HTML

inputs if there were any.

Let’s add some code to look at the inputs collection directly.

Looking at the input values

using System;

using System.Collections.Specialized;

public partial class Demo : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

if (IsPostBack)

{

NameValueCollection inputs = Request.Form;

String Last_Name = inputs["tbLastName"];

String First_Name = inputs["tbFirstName"];

String Gender = inputs["Gender"];

String CSE_Dept_Major = inputs["cbCSEDeptMajor"];

String Classification = inputs["ddlClassification"];

}

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Note C# indexer syntax.

Request.Form holds all inputs as Name-Value pairs

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QuickWatch for an Input Value

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The Gender Input

Note that there is only one input for the gender RadioButton group. Name is the ASPX controls' GroupName Value is the ID of the checked radio button.

Contrast to representation as object properties.

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New Page on Browser

Inputs are still set up. (Unlike .html)

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What the Browser Received

End of Section

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Refinements

We have seen the basic functionality of an ASPX web app.

Next we will look at a number of refinements. Get a deeper understanding of ASPX controls. Get some tips about page design.

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Setting the Focus

No control has the focus when the form is first displayed.

We have to click on the Last Name textbox in order to enter text.

The app can set the focus programatically using the Focus method of any input.

This is implemented by a JavaScript script created by IIS and sent to the browser along with the translated ASPX page.

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Setting the Focus

protected void Page_Load(object sender, EventArgs e)

{

if (IsPostBack)

{

NameValueCollection inputs = Request.Form;

String Last_Name = inputs["tbLastName"];

String First_Name = inputs["tbLastName"];

String Gender = inputs["Gender"];

String CSE_Dept_Major = inputs["cbCseMajor"];

String Classification = inputs["ddlClassification"];

}

else

{

tbLastName.Focus();

}

}

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Advancing the Focus

Users expect to move the focus to the next control by hitting tab. Currently this doesn’t work right.

Controlled by TabIndex property of the controls. Go to control with next higher value. Skip over values of 0.

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Controlling Tab Order

Set TabIndex property of tbLastName and tbFirstName to 1 and 2. Leave others set to 0.

Try it!

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The Default Button

We can specify a button to be automatically clicked if the user hit the Enter key.

Set the DefaultButton property of the <form> tag.

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The Default Button

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The Default Button