Developer Scripts

29 Nov 2013

ASP.NET Web Forms - XML Files

We can bind an XML file to a list control.

An XML File

Here is an XML file named "countries.xml":

<?xml version="1.0" encoding="ISO-8859-1"?>

<countries>

<country>
  <text>Norway</text>
  <value>N</value>
</country>

<country>
  <text>Sweden</text>
  <value>S</value>
</country>

<country>
  <text>France</text>
  <value>F</value>
</country>

<country>
  <text>Italy</text>
  <value>I</value>
</country>

</countries>

Take a look at the XML file: countries.xml

Bind a DataSet to a List Control

First, import the "System.Data" namespace. We need this namespace to work with DataSet objects. Include the following directive at the top of an .aspx page:

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

Next, create a DataSet for the XML file and load the XML file into the DataSet when the page is first loaded:

<script runat="server">
sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New DataSet
  mycountries.ReadXml(MapPath("countries.xml"))
end if
end sub

To bind the DataSet 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 XML DataSet:

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

<script runat="server">
sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New DataSet
  mycountries.ReadXml(MapPath("countries.xml"))
  rb.DataSource=mycountries
  rb.DataValueField="value"
  rb.DataTextField="text"
  rb.DataBind()
end if
end sub
</script>

<html>
<body>

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

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

<script runat="server">
sub Page_Load
if Not Page.IsPostBack then
  dim mycountries=New DataSet
  mycountries.ReadXml(MapPath("countries.xml"))
  rb.DataSource=mycountries
  rb.DataValueField="value"
  rb.DataTextField="text"
  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>

Show example »

26 Nov 2013

ASP.NET Web Forms - The SortedList Object

The SortedList object combines the features of both the ArrayList object and the Hashtable object.

Try it Yourself - Examples

SortedList RadiobuttonList 1

SortedList RadiobuttonList 2

SortedList DropDownList

The SortedList Object

The SortedList object contains items in key/value pairs. A SortedList object automatically sort the items in alphabetic or numeric order.

Items are added to the SortedList with the Add() method. A SortedList can be sized to its final size with the TrimToSize() method.

The following code creates a SortedList named mycountries and four elements are added:

<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")
end if
end sub
</script>

Data Binding

A SortedList 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 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
</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 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>

<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>

Show example »

ASP.NET Web Forms - The Hashtable Object

The Hashtable object contains items in key/value pairs.

Try it Yourself - Examples

Hashtable RadiobuttonList 1

Hashtable RadiobuttonList 2

Hashtable DropDownList

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>

Show example »

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

24 Nov 2013

ASP.NET Web Forms - The ArrayList Object

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

Try it Yourself - Examples

ArrayList DropDownList

ArrayList RadioButtonList

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>

Show example »

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.

ASP.NET Web Forms - Data Binding

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.

17 Nov 2013

ASP.NET Web Forms - The Button Control

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>

Show example »

ASP.NET Web Forms - The TextBox Control

The TextBox control is used to create a text box where the user can input text.

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>

Show example »

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.

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>

Show example »

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>

Show example »

13 Nov 2013

ASP.NET Web Forms - Maintaining the ViewState

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>

Show example »

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>

Show example »

ASP.NET Web Forms - HTML Forms

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.

7 Nov 2013

ASP.NET Web Forms - Events

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>

Show example »

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>

ASP.NET Web Forms - Server Controls

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 W3Schools!</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.w3schools.com"

End Sub

</script>

<html>

<body>

<form runat="server">

<a id="link1" runat="server">Visit W3Schools!</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>

5 Nov 2013

ASP.NET Web Forms - Events

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

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>

Show example »

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

The Page.IsPostBack Property

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>

ASP.NET Web Forms - Server Controls

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 W3Schools!</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.

<script runat="server">
Sub Page_Load
link1.HRef="http://www.w3schools.com"
End Sub
</script>

<html>
<body>

<form runat="server">
<a id="link1" runat="server">Visit W3Schools!</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.

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).

The syntax for creating a Validation server control is:

<asp:control_name id="some_id" runat="server" />

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>

Pages

29 Nov 2013

An XML File

Bind a DataSet to a List Control

Example

26 Nov 2013

Try it Yourself - Examples

The SortedList Object

Data Binding

Example

Try it Yourself - Examples

Create a Hashtable

Data Binding

Example

24 Nov 2013

Try it Yourself - Examples

Create an ArrayList

Data Binding to an ArrayList

Example

Data Binding

17 Nov 2013

The Button Control

Add a Script

Example

The TextBox Control

Example

Add a Script

Example

Example

13 Nov 2013

Maintaining the ViewState

Example

Example

ASP.NET Web Forms

Submitting a Form

7 Nov 2013

ASP.NET - Event Handlers

The Page_Load Event

Example

The Page.IsPostBack Property

Example

Limitations in Classic ASP

ASP.NET - Server Controls

ASP.NET - HTML Server Controls

ASP.NET - Web Server Controls

ASP.NET - Validation Server Controls

Example

5 Nov 2013

ASP.NET - Event Handlers

The Page_Load Event

Example

The Page.IsPostBack Property

Example

Limitations in Classic ASP

ASP.NET - Server Controls

ASP.NET - HTML Server Controls

ASP.NET - Web Server Controls

ASP.NET - Validation Server Controls

Example