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Thursday, January 15, 2015

ASP.NET Web Forms - Tutorial

ASP.NET Web Forms - Tutorial

Where to Start?

Many developers like to start learning a new technology by looking at working examples.
If you want to take a look at a working Web Forms examples, follow the ASP.NET Web Forms Demo.


What is Web Forms?

Web Forms is one of the 3 programming models for creating ASP.NET web sites and web applications.
The other two programming models are Web Pages and MVC (Model, View, Controller).
Web Forms is the oldest ASP.NET programming model, with event driven web pages written as a combination of HTML, server controls, and server code.
Web Forms are compiled and executed on the server, which generates the HTML that displays the web pages.
Web Forms comes with hundreds of different web controls and web components to build user-driven web sites with data access.

Visual Studio Express 2012/2010

Visual Studio Express is a free version of Microsoft Visual Studio.
Visual Studio Express is a development tool tailor made for Web Forms (and MVC).
Visual Studio Express contains:
  • MVC and Web Forms
  • Drag-and-drop web controls and web components
  • A web server language (Razor using VB or C#)
  • A web server (IIS Express)
  • A database server (SQL Server Compact)
  • A full web development framework (ASP.NET)
If you install Visual Studio Express, you will get more benefits from this tutorial.
If you want to install Visual Studio Express, click on one of these links:
Visual Web Developer 2012 (If you have Windows 7 or Windows 8)
Visual Web Developer 2010 (If you have Windows Vista or XP)

Hello online academy in HTML

This code displays the example as an HTML page:
<html>
<body bgcolor="yellow">
<center>
<h2>Hello online academy!</h2>
</center>
</body>
</html>
If you want to try it yourself, save the code in a file called "firstpage.htm".

Hello online academy in ASP.NET

The simplest way to convert an HTML page into an ASP.NET page is to copy the HTML file to a new file with an.aspx extension.
This code displays our example as an ASP.NET page:
<html>
<body bgcolor="yellow">
<center>
<h2>Hello online academy!</h2>
</center>
</body>
</html>
If you want to try it yourself, save the code in a file called "firstpage.aspx"

How Does it Work?

Fundamentally an ASP.NET page is just the same as an HTML page.
An HTML page has the extension .htm. If a browser requests an HTML page from the server, the server sends the page to the browser without any modifications.
An ASP.NET page has the extension .aspx. If a browser requests an ASP.NET page, the server processes any executable code in the page, before the result is sent back to the browser.
The ASP.NET page above does not contain any executable code, so nothing is executed. In the next examples we will add some executable code to the page to demonstrate the difference between static HTML pages and dynamic ASP pages.

Classic ASP

Active Server Pages (ASP) has been around for several years. With ASP, executable code can be placed inside HTML pages.
Previous versions of ASP (before ASP .NET) are often called Classic ASP.
ASP.NET is not fully compatible with Classic ASP, but most Classic ASP pages will work fine as ASP.NET pages, with only minor changes.

Dynamic Page in Classic ASP

To demonstrate how ASP can display pages with dynamic content, we have added some executable code (in red) to the previous example:
<html>
<body bgcolor="yellow">
<center>
<h2>Hello online academy!</h2>
<p><%Response.Write(Now())%></p>
</center>
</body>
</html>
The code inside the <% --%> tags is executed on the server.
Response.Write is ASP code for writing something to the HTML output stream.
Now() is a function returning the servers current date and time.
If you want to try it yourself, save the code in a file called "dynpage.asp", and create a link to the file like this:dynpage.asp

Dynamic Page in ASP .NET

This following code displays our example as an ASP.NET page:
<html>
<body bgcolor="yellow">
<center>
<h2>Hello online academy!</h2>
<p><%Response.Write(Now())%></p>
</center>
</body>
</html>
If you want to try it yourself, save the code in a file called "dynpage.aspx".

ASP.NET vs Classic ASP

The previous examples didn't demonstrate any differences between ASP.NET and Classic ASP.
As you can see from the two latest examples there are no differences between the two ASP and ASP.NET pages.
In the next chapters you will see how server controls make ASP.NET more powerful than Classic ASP.



Server controls are tags that are understood by the server.

Limitations in Classic ASP

The listing below was copied from the previous chapter:
<html>
<body bgcolor="yellow">
<center>
<h2>Hello online academy!</h2>
<p><%Response.Write(now())%></p>
</center>
</body>
</html>
The code above illustrates a limitation in Classic ASP: The code block has to be placed where you want the output to appear.
With Classic ASP it is impossible to separate executable code from the HTML itself. This makes the page difficult to read, and difficult to maintain.

ASP.NET - Server Controls

ASP.NET has solved the "spaghetti-code" problem described above with server controls.
Server controls are tags that are understood by the server.
There are three kinds of server controls:
  • HTML Server Controls - Traditional HTML tags
  • Web Server Controls - New ASP.NET tags
  • Validation Server Controls - For input validation

ASP.NET - HTML Server Controls

HTML server controls are HTML tags understood by the server.
HTML elements in ASP.NET files are, by default, treated as text. To make these elements programmable, add a runat="server" attribute to the HTML element. This attribute indicates that the element should be treated as a server control. The id attribute is added to identify the server control. The id reference can be used to manipulate the server control at run time.
Note: All HTML server controls must be within a <form> tag with the runat="server" attribute. The runat="server" attribute indicates that the form should be processed on the server. It also indicates that the enclosed controls can be accessed by server scripts.
In the following example we declare an HtmlAnchor server control in an .aspx file. Then we manipulate the HRef attribute of the HtmlAnchor control in an event handler (an event handler is a subroutine that executes code for a given event). The Page_Load event is one of many events that ASP.NET understands:
<script runat="server">
Sub Page_Load
link1.HRef="http://www.online academy.com"
End Sub
</script>

<html>
<body>

<form runat="server">
<a id="link1" runat="server">Visit online academy!</a>
</form>

</body>
</html>
The executable code itself has been moved outside the HTML.

ASP.NET - Web Server Controls

Web server controls are special ASP.NET tags understood by the server.
Like HTML server controls, Web server controls are also created on the server and they require a runat="server" attribute to work. However, Web server controls do not necessarily map to any existing HTML elements and they may represent more complex elements.
The syntax for creating a Web server control is:
<asp:control_name id="some_id" runat="server" />
In the following example we declare a Button server control in an .aspx file. Then we create an event handler for the Click event which changes the text on the button:
<script runat="server">
Sub submit(Source As Object, e As EventArgs)
button1.Text="You clicked me!"
End Sub
</script>

<html>
<body>

<form runat="server">
<asp:Button id="button1" Text="Click me!"
runat="server" OnClick="submit"/>
</form>

</body>
</html>

ASP.NET - Validation Server Controls

Validation server controls are used to validate user-input. If the user-input does not pass validation, it will display an error message to the user.
Each validation control performs a specific type of validation (like validating against a specific value or a range of values).
By default, page validation is performed when a Button, ImageButton, or LinkButton control is clicked. You can prevent validation when a button control is clicked by setting the CausesValidation property to false.
The syntax for creating a Validation server control is:
<asp:control_name id="some_id" runat="server" />
In the following example we declare one TextBox control, one Button control, and one RangeValidator control in an .aspx file. If validation fails, the text "The value must be from 1 to 100!" will be displayed in the RangeValidator control:

Example

<html>
<body>

<form runat="server">
<p>Enter a number from 1 to 100:
<asp:TextBox id="tbox1" runat="server" />
<br /><br />
<asp:Button Text="Submit" runat="server" />
</p>

<p>
<asp:RangeValidator
ControlToValidate="tbox1"
MinimumValue="1"
MaximumValue="100"
Type="Integer"
Text="The value must be from 1 to 100!"
runat="server" />
</p>
</form>

</body>
</html>

An Event Handler is a subroutine that executes code for a given event.

ASP.NET - Event Handlers

Look at the following code:
<%
lbl1.Text="The date and time is " & now()
%>

<html>
<body>
<form runat="server">
<h3><asp:label id="lbl1" runat="server" /></h3>
</form>
</body>
</html>
When will the code above be executed? The answer is: "You don't know..."

The Page_Load Event

The Page_Load event is one of many events that ASP.NET understands. The Page_Load event is triggered when a page loads, and ASP.NET will automatically call the subroutine Page_Load, and execute the code inside it:
Example

<script runat="server">
Sub Page_Load
lbl1.Text="The date and time is " & now()
End Sub
</script>

<html>
<body>
<form runat="server">
<h3><asp:label id="lbl1" runat="server" /></h3>
</form>
</body>
</html>

Note: The Page_Load event contains no object references or event arguments!

The Page.IsPostBack Property

The Page_Load subroutine runs EVERY time the page is loaded. If you want to execute the code in the Page_Load subroutine only the FIRST time the page is loaded, you can use the Page.IsPostBack property. If the Page.IsPostBack property is false, the page is loaded for the first time, if it is true, the page is posted back to the server (i.e. from a button click on a form):

Example
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  lbl1.Text="The date and time is " & now()
end if

End Sub

Sub submit(s As Object, e As EventArgs)
lbl2.Text="Hello World!"
End Sub
</script>

<html>
<body>
<form runat="server">
<h3><asp:label id="lbl1" runat="server" /></h3>
<h3><asp:label id="lbl2" runat="server" /></h3>
<asp:button text="Submit" onclick="submit" runat="server" />
</form>
</body>
</html>

The example above will write the "The date and time is...." message only the first time the page is loaded. When a user clicks on the Submit button, the submit subroutine will write "Hello World!" to the second label, but the date and time in the first label will not change.

All server controls must appear within a <form> tag, and the <form> tag must contain the runat="server" attribute.

ASP.NET Web Forms

All server controls must appear within a <form> tag, and the <form> tag must contain the runat="server" attribute. The runat="server" attribute indicates that the form should be processed on the server. It also indicates that the enclosed controls can be accessed by server scripts:
<form runat="server">

...HTML + server controls

</form>
Note: The form is always submitted to the page itself. If you specify an action attribute, it is ignored. If you omit the method attribute, it will be set to method="post" by default. Also, if you do not specify the name and id attributes, they are automatically assigned by ASP.NET.
Note: An .aspx page can only contain ONE <form runat="server"> control!
If you select view source in an .aspx page containing a form with no name, method, action, or id attribute specified, you will see that ASP.NET has added these attributes to the form. It looks something like this:
<form name="_ctl0" method="post" action="page.aspx" id="_ctl0">

...some code

</form>

Submitting a Form

A form is most often submitted by clicking on a button. The Button server control in ASP.NET has the following format:
<asp:Button id="id" text="label" OnClick="sub" runat="server" />
The id attribute defines a unique name for the button and the text attribute assigns a label to the button. The onClick event handler specifies a named subroutine to execute.
In the following example we declare a Button control in an .aspx file. A button click runs a subroutine which changes the text on the button:

<script  runat="server">
Sub submit(Source As Object, e As EventArgs)
   button1.Text="You clicked me!"
End Sub
</script>
<!DOCTYPE html>
<html>
<body>
<form runat="server">
<asp:Button id="button1" Text="Click me!" runat="server" OnClick="submit" />
</form>
</body>
</html>

You may save a lot of coding by maintaining the ViewState of the objects in your Web Form.

Maintaining the ViewState

When a form is submitted in classic ASP, all form values are cleared. Suppose you have submitted a form with a lot of information and the server comes back with an error. You will have to go back to the form and correct the information. You click the back button, and what happens.......ALL form values are CLEARED, and you will have to start all over again! The site did not maintain your ViewState.
When a form is submitted in ASP .NET, the form reappears in the browser window together with all form values. How come? This is because ASP .NET maintains your ViewState. The ViewState indicates the status of the page when submitted to the server. The status is defined through a hidden field placed on each page with a <form runat="server"> control. The source could look something like this:
<form name="_ctl0" method="post" action="page.aspx" id="_ctl0">
<input type="hidden" name="__VIEWSTATE"
value="dDwtNTI0ODU5MDE1Ozs+ZBCF2ryjMpeVgUrY2eTj79HNl4Q=" />

.....some code

</form>
Maintaining the ViewState is the default setting for ASP.NET Web Forms. If you want to NOT maintain the ViewState, include the directive <%@ Page EnableViewState="false" %> at the top of an .aspx page or add the attribute EnableViewState="false" to any control.
Look at the following .aspx file. It demonstrates the "old" way to do it. When you click on the submit button, the form value will disappear:

Example

<html>
<body>

<form action="demo_classicasp.aspx" method="post">
Your name: <input type="text" name="fname" size="20">
<input type="submit" value="Submit">
</form>
<%
dim fname
fname=Request.Form("fname")
If fname<>"" Then
Response.Write("Hello " & fname & "!")
End If
%>

</body>
</html>

Here is the new ASP .NET way. When you click on the submit button, the form value will NOT disappear:

Example

Click view source in the right frame of the example to see that ASP .NET has added a hidden field in the form to maintain the ViewState
<script runat="server">
Sub submit(sender As Object, e As EventArgs)
lbl1.Text="Hello " & txt1.Text & "!"
End Sub
</script>
<html>
<body>
<form runat="server">
Your name: <asp:TextBox id="txt1" runat="server" />
<asp:Button OnClick="submit" Text="Submit" runat="server" />
<p><asp:Label id="lbl1" runat="server" /></p>
</form>
</body>
</html>

The TextBox Control

The TextBox control is used to create a text box where the user can input text.
The TextBox control's attributes and properties are listed in our web controls reference page.
The example below demonstrates some of the attributes you may use with the TextBox control:

Example

<html>
<body>

<form runat="server">

A basic TextBox:
<asp:TextBox id="tb1" runat="server" />
<br /><br />

A password TextBox:
<asp:TextBox id="tb2" TextMode="password" runat="server" />
<br /><br />

A TextBox with text:
<asp:TextBox id="tb4" Text="Hello World!" runat="server" />
<br /><br />

A multiline TextBox:
<asp:TextBox id="tb3" TextMode="multiline" runat="server" />
<br /><br />

A TextBox with height:
<asp:TextBox id="tb6" rows="5" TextMode="multiline"
runat="server" />
<br /><br />

A TextBox with width:
<asp:TextBox id="tb5" columns="30" runat="server" />

</form>

</body>
</html>

Add a Script

The contents and settings of a TextBox control may be changed by server scripts when a form is submitted. A form can be submitted by clicking on a button or when a user changes the value in the TextBox control.
In the following example we declare one TextBox control, one Button control, and one Label control in an .aspx file. When the submit button is triggered, the submit subroutine is executed. The submit subroutine writes a text to the Label control:

Example

<script runat="server">
Sub submit(sender As Object, e As EventArgs)
lbl1.Text="Your name is " & txt1.Text
End Sub
</script>

<html>
<body>

<form runat="server">
Enter your name:
<asp:TextBox id="txt1" runat="server" />
<asp:Button OnClick="submit" Text="Submit" runat="server" />
<p><asp:Label id="lbl1" runat="server" /></p>
</form>

</body>
</html>

In the following example we declare one TextBox control and one Label control in an .aspx file. When you change the value in the TextBox and either click outside the TextBox or press the Tab key, the change subroutine is executed. The submit subroutine writes a text to the Label control:

Example

<script runat="server">
Sub change(sender As Object, e As EventArgs)
lbl1.Text="You changed text to " & txt1.Text
End Sub
</script>

<html>
<body>

<form runat="server">
Enter your name:
<asp:TextBox id="txt1" runat="server"
text="Hello World!"
ontextchanged="change" autopostback="true"/>
<p><asp:Label id="lbl1" runat="server" /></p>
</form>

</body>
</html>
The Button control is used to display a push button.

The Button Control

The Button control is used to display a push button. The push button may be a submit button or a command button. By default, this control is a submit button.
A submit button does not have a command name and it posts the page back to the server when it is clicked. It is possible to write an event handler to control the actions performed when the submit button is clicked.
A command button has a command name and allows you to create multiple Button controls on a page. It is possible to write an event handler to control the actions performed when the command button is clicked.
The Button control's attributes and properties are listed in our web controls reference page.
The example below demonstrates a simple Button control:
<html>
<body>

<form runat="server">
<asp:Button id="b1" Text="Submit" runat="server" />
</form>

</body>
</html>

Add a Script

A form is most often submitted by clicking on a button.
In the following example we declare one TextBox control, one Button control, and one Label control in an .aspx file. When the submit button is triggered, the submit subroutine is executed. The submit subroutine writes a text to the Label control:

Example

<script runat="server">
Sub submit(sender As Object, e As EventArgs)
lbl1.Text="Your name is " & txt1.Text
End Sub
</script>

<html>
<body>

<form runat="server">
Enter your name:
<asp:TextBox id="txt1" runat="server" />
<asp:Button OnClick="submit" Text="Submit" runat="server" />
<p><asp:Label id="lbl1" runat="server" /></p>
</form>

</body>
</html>

We may use data binding to fill lists with selectable items from an imported data source, like a database, an XML file, or a script.

Data Binding

The following controls are list controls which support data binding:
  • asp:RadioButtonList
  • asp:CheckBoxList
  • asp:DropDownList
  • asp:Listbox
The selectable items in each of the above controls are usually defined by one or more asp:ListItem controls, like this:
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="countrylist" runat="server">
<asp:ListItem value="N" text="Norway" />
<asp:ListItem value="S" text="Sweden" />
<asp:ListItem value="F" text="France" />
<asp:ListItem value="I" text="Italy" />
</asp:RadioButtonList>
</form>

</body>

</html>
However, with data binding we may use a separate source, like a database, an XML file, or a script to fill the list with selectable items.
By using an imported source, the data is separated from the HTML, and any changes to the items are made in the separate data source.
In the next three chapters, we will describe how to bind data from a scripted data source.

The ArrayList Object

The ArrayList object is a collection of items containing a single data value.

Examples

ArrayList DropDownList
<script  runat="server">
sub Page_Load
if Not Page.IsPostBack then
   dim mycountries=New ArrayList
   mycountries.Add("Norway")
   mycountries.Add("Sweden")
   mycountries.Add("France")
   mycountries.Add("Italy")
   mycountries.TrimToSize()
   mycountries.Sort()
   dd.DataSource=mycountries
   dd.DataBind()
end if
end sub

sub displayMessage(s as Object,e As EventArgs)
lbl1.text="Your favorite country is: " & dd.SelectedItem.Text
end sub
</script>

<!DOCTYPE html>
<html>
<body>

<form runat="server">
<asp:DropDownList id="dd" runat="server"
AutoPostBack="True" onSelectedIndexChanged="displayMessage" />
<p><asp:label id="lbl1" runat="server" /></p>
</form>

</body>
</html>

ArrayList RadioButtonList
<script  runat="server">
Sub Page_Load
if Not Page.IsPostBack then
   dim mycountries=New ArrayList
   mycountries.Add("Norway")
   mycountries.Add("Sweden")
   mycountries.Add("France")
   mycountries.Add("Italy")
   mycountries.TrimToSize()
   mycountries.Sort()
   rb.DataSource=mycountries
   rb.DataBind()
end if
end sub

sub displayMessage(s as Object,e As EventArgs)
lbl1.text="Your favorite country is: " & rb.SelectedItem.Text
end sub
</script>

<!DOCTYPE html>
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server"
AutoPostBack="True" onSelectedIndexChanged="displayMessage" />
<p><asp:label id="lbl1" runat="server" /></p>
</form>

</body>
</html>

Create an ArrayList

The ArrayList object is a collection of items containing a single data value.
Items are added to the ArrayList with the Add() method.
The following code creates a new ArrayList object named mycountries and four items are added:
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
end if
end sub
</script>
By default, an ArrayList object contains 16 entries. An ArrayList can be sized to its final size with the TrimToSize() method:
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
  mycountries.TrimToSize()
end if
end sub
</script>
An ArrayList can also be sorted alphabetically or numerically with the Sort() method:
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
  mycountries.TrimToSize()
  mycountries.Sort()
end if
end sub
</script>
To sort in reverse order, apply the Reverse() method after the Sort() method:
<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
  mycountries.TrimToSize()
  mycountries.Sort()
  mycountries.Reverse()
end if
end sub
</script>

Data Binding to an ArrayList

An ArrayList object may automatically generate the text and values to the following controls:
  • asp:RadioButtonList
  • asp:CheckBoxList
  • asp:DropDownList
  • asp:Listbox
To bind data to a RadioButtonList control, first create a RadioButtonList control (without any asp:ListItem elements) in an .aspx page:
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server" />
</form>

</body>
</html>
Then add the script that builds the list and binds the values in the list to the RadioButtonList control:

Example

<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New ArrayList
  mycountries.Add("Norway")
  mycountries.Add("Sweden")
  mycountries.Add("France")
  mycountries.Add("Italy")
  mycountries.TrimToSize()
  mycountries.Sort()
  rb.DataSource=mycountries
  rb.DataBind()
end if
end sub
</script>

<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server" />
</form>

</body>
</html>

The DataSource property of the RadioButtonList control is set to the ArrayList and it defines the data source of the RadioButtonList control. The DataBind() method of the RadioButtonList control binds the data source with the RadioButtonList control.
Note: The data values are used as both the Text and Value properties for the control. To add Values that are different from the Text, use either the Hashtable object or the SortedList object.

The Hashtable Object

Examples

Hashtable RadiobuttonList 1
<script  runat="server">
sub Page_Load
if Not Page.IsPostBack then
   dim mycountries=New Hashtable
   mycountries.Add("N","Norway")
   mycountries.Add("S","Sweden")
   mycountries.Add("F","France")
   mycountries.Add("I","Italy")
   rb.DataSource=mycountries
   rb.DataValueField="Key"
   rb.DataTextField="Value"
   rb.DataBind()
end if
end sub

sub displayMessage(s as Object,e As EventArgs)
lbl1.text="Your favorite country is: " & rb.SelectedItem.Text
end sub
</script>

<!DOCTYPE html>
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server"
AutoPostBack="True" onSelectedIndexChanged="displayMessage" />
<p><asp:label id="lbl1" runat="server" /></p>
</form>

</body>
</html>

Hashtable RadiobuttonList 2

<script  runat="server">
sub Page_Load
if Not Page.IsPostBack then
   dim navigate=New Hashtable
   navigate.Add("RadioButtonList","control_radiobuttonlist.asp")
   navigate.Add("CheckBoxList","control_checkboxlist.asp")
   navigate.Add("DropDownList","control_dropdownlist.asp")
   navigate.Add("ListBox","control_listbox.asp")
   rb.DataSource=navigate
   rb.DataValueField="Value"
   rb.DataTextField="Key"
   rb.DataBind()
end if
end sub

sub navigate(s as Object, e As EventArgs)
response.redirect(rb.SelectedItem.Value)
end sub
</script>

<!DOCTYPE html>
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server"
AutoPostBack="True" onSelectedIndexChanged="navigate" />
</form>

</body>
</html>

Hashtable DropDownList
<script  runat="server">
sub Page_Load
if Not Page.IsPostBack then
   dim mycountries=New Hashtable
   mycountries.Add("N","Norway")
   mycountries.Add("S","Sweden")
   mycountries.Add("F","France")
   mycountries.Add("I","Italy")
   dd.DataSource=mycountries
   dd.DataValueField="Key"
   dd.DataTextField="Value"
   dd.DataBind()
end if
end sub

sub displayMessage(s as Object,e As EventArgs)
lbl1.text="Your favorite country is: " & dd.SelectedItem.Text
end sub
</script>

<!DOCTYPE html>
<html>
<body>

<form runat="server">
<asp:DropDownList id="dd" runat="server"
AutoPostBack="True" onSelectedIndexChanged="displayMessage" />
<p><asp:label id="lbl1" runat="server" /></p>
</form>

</body>
</html>

Create a Hashtable

The Hashtable object contains items in key/value pairs. The keys are used as indexes, and very quick searches can be made for values by searching through their keys.
Items are added to the Hashtable with the Add() method.
The following code creates a Hashtable named mycountries and four elements are added:

<script runat="server">
Sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New Hashtable
  mycountries.Add("N","Norway")
  mycountries.Add("S","Sweden")
  mycountries.Add("F","France")
  mycountries.Add("I","Italy")
end if
end sub
</script>

Data Binding

A Hashtable object may automatically generate the text and values to the following controls:
  • asp:RadioButtonList
  • asp:CheckBoxList
  • asp:DropDownList
  • asp:Listbox
To bind data to a RadioButtonList control, first create a RadioButtonList control (without any asp:ListItem elements) in an .aspx page:
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server" AutoPostBack="True" />
</form>

</body>
</html>
Then add the script that builds the list:
<script runat="server">
sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New Hashtable
  mycountries.Add("N","Norway")
  mycountries.Add("S","Sweden")
  mycountries.Add("F","France")
  mycountries.Add("I","Italy")
  rb.DataSource=mycountries
  rb.DataValueField="Key"
  rb.DataTextField="Value"
  rb.DataBind()
end if
end sub
</script>

<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server" AutoPostBack="True" />
</form>

</body>
</html>
Then we add a sub routine to be executed when the user clicks on an item in the RadioButtonList control. When a radio button is clicked, a text will appear in a label:

Example

<script runat="server">
sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New Hashtable
  mycountries.Add("N","Norway")
  mycountries.Add("S","Sweden")
  mycountries.Add("F","France")
  mycountries.Add("I","Italy")
  rb.DataSource=mycountries
  rb.DataValueField="Key"
  rb.DataTextField="Value"
  rb.DataBind()
end if
end sub

sub displayMessage(s as Object,e As EventArgs)
lbl1.text="Your favorite country is: " & rb.SelectedItem.Text
end sub
</script>

<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server"
AutoPostBack="True" onSelectedIndexChanged="displayMessage" />
<p><asp:label id="lbl1" runat="server" /></p>
</form>

</body>
</html>

Note: You cannot choose the sort order of the items added to the Hashtable. To sort items alphabetically or numerically, use the SortedList object.

The SortedList Object

Examples

SortedList RadiobuttonList 1
<script  runat="server">
sub Page_Load
if Not Page.IsPostBack then
   dim mycountries=New SortedList
   mycountries.Add("N","Norway")
   mycountries.Add("S","Sweden")
   mycountries.Add("F","France")
   mycountries.Add("I","Italy")
   rb.DataSource=mycountries
   rb.DataValueField="Key"
   rb.DataTextField="Value"
   rb.DataBind()
end if
end sub

sub displayMessage(s as Object,e As EventArgs)
lbl1.text="Your favorite country is: " & rb.SelectedItem.Text
end sub
</script>

<!DOCTYPE html>
<html>
<body>

<form runat="server">
<asp:RadioButtonList id="rb" runat="server"
AutoPostBack="True" onSelectedIndexChanged="displayMessage" />
<p><asp:label id="lbl1" runat="server" /></p>
</form>

</body>
</html>


SortedList RadiobuttonList 2
<script  runat="server">
sub Page_Load
if Not Page.IsPostBack then
   dim navigate=New SortedList
   navigate.Add("RadioButtonList","control_radiobuttonlist.asp")
   navigate.Add("CheckBoxList","control_checkboxlist.asp")
   navigate.Add("DropDownList","control_dropdownlist.asp")
   navigate.Add("ListBox","control_listbox.asp")
   rb.DataSource=navigate
   rb.DataValueField="Value"
   rb.DataTextField="Key"
   rb.DataBind()
end if
end sub

sub navigate(s as Object, e As EventArgs)
response.redirect(rb.SelectedItem.Value)
end sub
</script>
<!DOCTYPE html>
<html>
<body>
<form runat="server">
<asp:RadioButtonList id="rb" runat="server"
AutoPostBack="True" onSelectedIndexChanged="navigate" />
</form>
</body>
</html>


SortedList DropDownList

<script  runat="server">
sub Page_Load
if Not Page.IsPostBack then
   dim mycountries=New SortedList
   mycountries.Add("N","Norway")
   mycountries.Add("S","Sweden")
   mycountries.Add("F","France")
   mycountries.Add("I","Italy")
   dd.DataSource=mycountries
   dd.DataValueField="Key"
   dd.DataTextField="Value"
   dd.DataBind()
end if
end sub

sub displayMessage(s as Object,e As EventArgs)
lbl1.text="Your favorite country is: " & dd.SelectedItem.Text
end sub
</script>
<!DOCTYPE html>
<html>
<body>
<form runat="server">
<asp:DropDownList id="dd" runat="server"
AutoPostBack="True" onSelectedIndexChanged="displayMessage" />
<p><asp:label id="lbl1" runat="server" /></p>
</form>
</body>
</html>

What is ADO.NET?

    • ADO.NET is a part of the .NET Framework
    • ADO.NET consists of a set of classes used to handle data access
  • ADO.NET is entirely based on XML
  • ADO.NET has, unlike ADO, no Recordset object

Create a Database Connection

We are going to use the Northwind database in our examples.
First, import the "System.Data.OleDb" namespace. We need this namespace to work with Microsoft Access and other OLE DB database providers. We will create the connection to the database in the Page_Load subroutine. We create a dbconn variable as a new OleDbConnection class with a connection string which identifies the OLE DB provider and the location of the database. Then we open the database connection:
<%@ Import Namespace="System.Data.OleDb" %>

<script runat="server">
sub Page_Load
dim dbconn
dbconn=New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;
data source=" & server.mappath("northwind.mdb"))
dbconn.Open()
end sub
</script>
Note: The connection string must be a continuous string without a line break!

Create a Database Command

To specify the records to retrieve from the database, we will create a dbcomm variable as a new OleDbCommand class. The OleDbCommand class is for issuing SQL queries against database tables:
<%@ Import Namespace="System.Data.OleDb" %>

<script runat="server">
sub Page_Load
dim dbconn,sql,dbcomm
dbconn=New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;
data source=" & server.mappath("northwind.mdb"))
dbconn.Open()
sql="SELECT * FROM customers"
dbcomm=New OleDbCommand(sql,dbconn)
end sub
</script>

Create a DataReader

The OleDbDataReader class is used to read a stream of records from a data source. A DataReader is created by calling the ExecuteReader method of the OleDbCommand object:
<%@ Import Namespace="System.Data.OleDb" %>

<script runat="server">
sub Page_Load
dim dbconn,sql,dbcomm,dbread
dbconn=New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;
data source=" & server.mappath("northwind.mdb"))
dbconn.Open()
sql="SELECT * FROM customers"
dbcomm=New OleDbCommand(sql,dbconn)
dbread=dbcomm.ExecuteReader()
end sub
</script>

Bind to a Repeater Control

Then we bind the DataReader to a Repeater control:

Example

<%@ Import Namespace="System.Data.OleDb" %>

<script runat="server">
sub Page_Load
dim dbconn,sql,dbcomm,dbread
dbconn=New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;
data source=" & server.mappath("northwind.mdb"))
dbconn.Open()
sql="SELECT * FROM customers"
dbcomm=New OleDbCommand(sql,dbconn)
dbread=dbcomm.ExecuteReader()
customers.DataSource=dbread
customers.DataBind()
dbread.Close()
dbconn.Close()
end sub
</script>

<html>
<body>

<form runat="server">
<asp:Repeater id="customers" runat="server">

<HeaderTemplate>
<table border="1" width="100%">
<tr>
<th>Companyname</th>
<th>Contactname</th>
<th>Address</th>
<th>City</th>
</tr>
</HeaderTemplate>

<ItemTemplate>
<tr>
<td><%#Container.DataItem("companyname")%></td>
<td><%#Container.DataItem("contactname")%></td>
<td><%#Container.DataItem("address")%></td>
<td><%#Container.DataItem("city")%></td>
</tr>
</ItemTemplate>

<FooterTemplate>
</table>
</FooterTemplate>

</asp:Repeater>
</form>

</body>
</html>

Close the Database Connection

Always close both the DataReader and database connection after access to the database is no longer required:
dbread.Close()
dbconn.Close()

Master Pages
Master pages provide templates for other pages on your web site.

Master Pages

Master pages allow you to create a consistent look and behavior for all the pages (or group of pages) in your web application.
A master page provides a template for other pages, with shared layout and functionality. The master page defines placeholders for the content, which can be overridden by content pages. The output result is a combination of the master page and the content page.
The content pages contain the content you want to display.
When users request the content page, ASP.NET merges the pages to produce output that combines the layout of the master page with the content of the content page.

Master Page Example

<%@ Master %>

<html>
<body>
<h1>Standard Header From Masterpage</h1>
<asp:ContentPlaceHolder id="CPH1" runat="server">
</asp:ContentPlaceHolder>
</body>
</html>
The master page above is a normal HTML page designed as a template for other pages.
The @ Master directive defines it as a master page.
The master page contains a placeholder tag <asp:ContentPlaceHolder> for individual content.
The id="CPH1" attribute identifies the placeholder, allowing many placeholders in the same master page.
This master page was saved with the name "master1.master".
Note: The master page can also contain code, allowing dynamic content.


Content Page Example

<%@ Page MasterPageFile="master1.master" %>

<asp:Content ContentPlaceHolderId="CPH1" runat="server">
  <h2>Individual Content</h2>
  <p>Paragraph 1</p>
  <p>Paragraph 2</p>
</asp:Content>
The content page above is one of the individual content pages of the web.
The @ Page directive defines it as a standard content page.
The content page contains a content tag <asp:Content> with a reference to the master page (ContentPlaceHolderId="CPH1").
This content page was saved with the name "mypage1.aspx".
When the user requests this page, ASP.NET merges the content page with the master page.
Click to display mypage1.aspx.
Note: The content text must be inside the <asp:Content> tag. No content is allowed outside the tag.


Content Page With Controls

<%@ Page MasterPageFile="master1.master" %>

<asp:Content ContentPlaceHolderId="CPH1" runat="server">
  <h2>online academy</h2>
  <form runat="server">
    <asp:TextBox id="textbox1" runat="server" />
    <asp:Button id="button1" runat="server" text="Button" />
  </form>
</asp:Content>
The content page above demonstrates how .NET controls can be inserted into the content page just like an into an ordinary page.
Click to display mypage2.aspx.

 Navigation

ASP.NET has built-in navigation controls

Web Site Navigation

Maintaining the menu of a large web site is difficult and time consuming.
In ASP.NET the menu can be stored in a file to make it easier to maintain. This file is normally called web.sitemap, and is stored in the root directory of the web.
In addition, ASP.NET has three new navigation controls:
  • Dynamic menus
  • TreeViews
  • Site Map Path

The Sitemap File

The following sitemap file is used in this tutorial:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<siteMap>
  <siteMapNode title="Home" url="/aspnet/w3home.aspx">
    <siteMapNode title="Services" url="/aspnet/w3services.aspx">
      <siteMapNode title="Training" url="/aspnet/w3training.aspx"/>
      <siteMapNode title="Support" url="/aspnet/w3support.aspx"/>
    </siteMapNode>
  </siteMapNode>
</siteMap>
Rules for creating a sitemap file:
  • The XML file must contain a <siteMap> tag surrounding the content
  • The <siteMap> tag can only have one <siteMapNode> child node (the "home" page)
  • Each <siteMapNode> can have several child nodes (web pages)
  • Each <siteMapNode> has attributes defining page title and URL
Note: The sitemap file must be placed in the root directory of the web and the URL attributes must be relative to the root directory.


Dynamic Menu

The <asp:Menu> control displays a standard site navigation menu.
Code Example:
<asp:SiteMapDataSource id="nav1" runat="server" />

<form runat="server">
<asp:Menu runat="server" DataSourceId="nav1" />
</form>
The <asp:Menu> control in the example above is a placeholder for a server created navigation menu.
The data source of the control is defined by the DataSourceId attribute. The id="nav1" connects it to the <asp:SiteMapDataSource> control.
The <asp:SiteMapDataSource> control automatically connects to the default sitemap file (web.sitemap).
Click here to see a demo of Menu, TreeView, and SiteMapPath

TreeView

The <asp:TreeView> control displays a multi level navigation menu.
The menu looks like a tree with branches that can be opened or closed with + or - symbol.
Code Example:
<asp:SiteMapDataSource id="nav1" runat="server" />

<form runat="server">
<asp:TreeView runat="server" DataSourceId="nav1" />
</form>
The <asp:TreeView> control in the example above is a placeholder for a server created navigation menu.
The data source of the control is defined by the DataSourceId attribute. The id="nav1" connects it to the <asp:SiteMapDataSource> control.
The <asp:SiteMapDataSource> control automatically connects to the default sitemap file (web.sitemap).
Click here to see a demo of Menu, TreeView, and SiteMapPath

SiteMapPath

The SiteMapPath control displays the trail (navigation path) to the current page. The path acts as clickable links to previous pages.
Unlike the TreeView and Menu control the SiteMapPath control does NOT use a SiteMapDataSource. The SiteMapPath control uses the web.sitemap file by default.
Tips: If the SiteMapPath displays incorrectly, most likely there is a URL error (typo) in the web.sitemap file.

Code Example:
<form runat="server">
<asp:SiteMapPath runat="server" />
</form>
The <asp:SiteMapPath> control in the example above is a placeholder for a server created site path display.
Click here to see a demo of Menu, TreeView, and SiteMapPath


Examples

ASP.NET HTML Controls

HTMLAnchor
HTMLButton
HTMLImage
HTMLImage 2
HTMLInputbutton
HTMLInputCheckbox
HTMLInputHidden
HTMLInputImage
HTMLInputRadiobutton
HTMLTable
HTMLTable 2
HTMLTextarea
ASP.NET Web Controls
AdRotator
Button
Button 2
Calendar
Calendar 2
Calendar 3
Checkbox
CheckboxList
DataList
DataList with styles
DataList with <AlternatingItemTemplate>
DropdownList
Hyperlink
Image
ImageButton
Label
LinkButton
Listbox
Literal
Literal 2
Panel
Radiobutton
RadiobuttonList
Repeater
Repeater with <AlternatingItemTemplate>
Repeater with <SeparatorTemplate>
Table
Table 2
Textbox
Textbox 2
Textbox 3
XML
ASP.NET Validation Controls
CompareValidator
CompareValidator 2
CustomValidator
RangeValidator
RangeValidator 2
RegularExpressionValidator
RequiredFieldValidator
Validationsummary
Validationsummary 2
ASP.NET Events
Page_Load
Page.IsPostBack
ASP.NET Data Binding
ArrayList RadioButtonList
ArrayList DropDownList
Hashtable RadioButtonList 1
Hashtable RadiobuttonList 2
Hashtable DropDownList
SortedList RadioButtonList 1
SortedList RadiobuttonList 2
SortedList DropDownList
XML RadiobuttonList
ASP.NET Database
Database connection - Bind to a Repeater control
Database connection - Bind to a DataList control



























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