April 2006 Entries

ASP.NET 2.0: XmlDataSource - Default Caching Feature

XmlDataSource is a wonderful Data Source control used to bind hierarchial data. It can be combined with a TreeView to display a Tree structure of Data to the users.

While implementing XmlDataSource, we may not get the Data updated even though we change the underlying data, due to the built-in caching feature of this control.

Let us examine the following scenario.

We have a XML Fragment retrieved from Database based on a user input and set as the Data for the XmlDatasource. Then, when the user input changes, we would be getting a different XML Fragment from the Database. However, you will find that when you bind the XmlDataSoruce to a control, the data doesnt change.

This is because, by default, the EnableCaching propery is set to "true". You can also find that the CacheDuration is set to "Infinite". This forces the Data in the XmlDataSource to be cached and hence the change in the underlying Data, wont get reflected.

The resolution is to set the EnableCaching property to false or specify a CacheKeyDependency, or set the CacheDuration to a lesser time.

Since it is by default set for caching and we dont explicitly set it, it may be a little surprising to see the stale data when dealing with XmlDataSources.

This is not the same with other DataSources like SqlDataSource, ObjectDataSource etc., which have the EnableCaching property set to false, by default.

Cheers and Happy Programming !!!

ASP.NET 2.0 - Enter Key - Default Submit Button

One of the most annoying things in developing web pages is handling the "Enter key" for form submission. Enter key has been the favourite way users like to submit forms. Though we provide Buttons to click on, the easiest and intuitive way is that, I can enter some text, make some changes and then hit "Enter" to accomplish my submission.

"Enter" Key is handled in a little tricky way by uplevel browsers like Internet Explorer, when it comes to ASP.NET.

  • If there is a single Textbox and single button, then it becomes straight forward, the button is submitted. However, the event code doesnt get executed, though the page postsback.

  • If there are two or more, buttons, then it takes up the first button as the default button. However, it still doesnt execute the event handler but just refreshes the page.

You can supress the Enter key event using Javascript. But this would result in other undesirable effects like, any Enter key in the form i.e. within Text Area or basically where large text is entered, would be disabled.

The earlier work around was to associate a javascript function to each Button to verify the that the relevant button is submitted upon Enter key.

ASP.NET 2.0 introduces a wonderful work around for this. By simply specifying the "defaultbutton" property to the ID of the <asp:Button>, whose event you want to fire, your job is done.

The defaultbutton property can be specified at the Form level in the form tag as well as at panel level in the <asp:panel> definition tag. The form level setting is overridden when specified at the panel level, for those controls that are inside the panel.

Also, the Event Handler for the specified button, fires thereby simulating a true submit button functionality.

The following sample code contains a form and 4 panels with each of them containing different buttons. It can be noticed that for each panel, there is a default button specified which would trigger the corresponding button's event handler when "Enter" Key is pressed upon a text changed event.

<form id="form1" runat="server" defaultbutton="btn1">


<asp:TextBox ID="txt" runat="server"></asp:TextBox>

<asp:Button ID="Button5" runat="server" Text="Cancel" OnClick="Button5_Click" />

<asp:Button ID="btn1" runat="server" Text="Submit" OnClick="btn1_Click" />

<asp:Panel ID="pnl1" runat="server" defaultbutton="Button1">

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>

<asp:Button ID="Button1" runat="server" Text="Button1" OnClick="Button1_Click" />


<asp:Panel ID="Panel1" runat="server" defaultbutton="Button2">

<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>

<asp:TextBox ID="TextBox4" runat="server"></asp:TextBox>

<asp:Button ID="Button2" runat="server" Text="Button2" OnClick="Button2_Click" />


<asp:Panel ID="Panel2" runat="server" defaultbutton="Button3">

<asp:TextBox ID="TextBox5" runat="server"></asp:TextBox>

<asp:TextBox ID="TextBox6" runat="server"></asp:TextBox>

<asp:Button ID="Button3" runat="server" Text="Button3" OnClick="Button3_Click" />


<asp:Panel ID="Panel3" runat="server" defaultbutton="Button4">

<asp:TextBox ID="TextBox7" runat="server"></asp:TextBox>

<asp:TextBox ID="TextBox8" runat="server"></asp:TextBox>

<asp:Button ID="Button4" runat="server" Text="Button4" OnClick="Button4_Click" />




The corresponding, sample events for the button clicks are

protected void Button1_Click(object sender, EventArgs e)

protected void Button2_Click(object sender, EventArgs e)

protected void Button3_Click(object sender, EventArgs e)

protected void Button4_Click(object sender, EventArgs e)

protected void btn1_Click(object sender, EventArgs e)

protected void Button5_Click(object sender, EventArgs e)

Once we execute the above functionality, we can notice, the corresponding Buttons' text are displayed when the Enter key is pressed from within a panel and at the form level, it fires the btn1 Button's event.

This would be a very useful feature in scenarios where we have different sections of the page and would like to have Enter key fire corresponding submit button events.

Cheers and Happy Enter Keying !!!