MSDN Style Choose a Language Extender

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  • Sample Application :

  • Source Code           :

Quite recently , someone asked me if there was a control that mimicked MSDN's "Choose a Language" Button.

It looks like this:



I would have explained that one could  achieve this using a combination of the DropDownExtender and some hacky javascript to prevent the popup from closing when one clicks on the options in the CheckBoxList.

But , this sounded to be a stupid way to solve the problem .And also , I was teaching a couple of guys how to write Ajax Control Extenders.
Since this looked like a good example to illustrate and also a pretty fun problem to solve , I went ahead and wrote a control Extender that does exactly this .

So , the behavior would be :

a) We have a CheckBoxList inside a block Element such as a asp:Panel , which is initially hidden
b) We have a button upon clicking on which the chechboxList is shown.
c) User can select multiple elements from the CheckBoxList.
   c.1) If One option is selected, the " Language Filter : " value would show the Option
   c.2) If more than one option is selected,  it would show "Multiple Options"

So , my extender looks like this .


Looks very much like the MSDN widget , doesn't it ?
So , how would one go about writing this extender ?

The design would be dependent on the Behavior that you want to achieve.

a) Are there any existing behaviors that you want to create that already exist ?
  You would want the Options to POPUP , so we need the PopupExtender.

b) What kind of Properties would the Extender exhibit ?

Property Name Description
TargetPanelID The Id of the asp:Panel that would contain the checkBoxList
PopupPosition The Position relative to the TargetControl where the Options would popup

c) What kind of Events would the Extender raise ?

Event Name Description EventArgs
itemSelected Raised when an item in the CheckBoxList is Selected The Checkbox , the text of the Checkbox , a value indicating if the checkbox is checked.

So , my design/spec is now ready .

I follow these steps to setup the initial infrastructure for my Extender : Creating a new extender
Being Thoroughly incompetent at finding the right name , I use the term "OptionPickerBehavior" to describe my extender and get 3 files ,

  1. OptionPickerBehavior.js
  2. OptionPickerBehaviorDesigner.cs
  3. OptionPickerBehaviorExtender.cs


In the OptionPickerBehaviorExtender.cs
Since we decided that I need the PopupExtender , I will need to add that as the RequiredScript for my extender.

 Defining the Properties 
We add the Necessary Properties 
        public string TargetPanelID
            get { return GetPropertyValue("targetPanelID", ""); }
            set { SetPropertyValue("targetPanelID", value); }
 We also define the other properties , PopupPosition and FilterText similarly .
 Defining the Event 
        public string OnClientItemSelected
            get { return GetPropertyValue("itemSelected", ""); }
            set { SetPropertyValue("itemSelected", value); }
 In the OptionPickerBehavior.js

The behavior of the control is defined in the accompanying OptionPickerBehavior.js file.
Now , here is where the real meat of the control lies , since its too tedious to describe the whole thing in One Blog Post ,
I have put up the control Extender and a Sample application for download , its available for you guys to download and try out .
I will blog about how we use JavaScript to Achieve the UI effect that you see.

 How do I use this control ? 

a) Reference the SampleExtenders Dll in your web project .
b) Add a tagMapping in your web.config for the SampleExtenders Controls .

      <add tagPrefix ="Raj" namespace="SampleExtenders" assembly="SampleExtenders"/>

c) Add an ImageButton to act as the Trigger Control .

 <asp:ImageButton runat="server" ID="btnToggleOptions" ImageUrl="~/images/Arrow-off.gif" />

d) The TargetPanel which contains the CheckBoxList.

 <!-- Target Panel Begins-->
<asp:Panel runat="server" ID="OptionsList" Style="display: none; width: 150px" CssClass="grey">
              <asp:CheckBoxList runat="server" ID="chklOptions">
                         <asp:ListItem Text="Visual Basic" Value="Visual Basic"></asp:ListItem>
                         <asp:ListItem Text="C#" Value="CSharp"></asp:ListItem>
                         <asp:ListItem Text="C++" Value="Visual Basic"></asp:ListItem>
                         <asp:ListItem Text="J#" Value="Visual Basic"></asp:ListItem>
                         <asp:ListItem Text="JScript" Value="Visual Basic"></asp:ListItem>
                         <asp:ListItem Text="XAML" Value="Visual Basic"></asp:ListItem>
<!-- Target Panel Ends-->

e) Markup for the OptionPickerExtender

  <Raj:OptionPickerBehavior runat="server" ID="optionList" 
            FilterText="Select Languages" 


 f) The itemSelected function is wired up to handle the click on the CheckBoxes in the CheckBoxList.
g) Thats it !! you are done !!
 Happy Coding .
 In case you have any questions , feel free to leave a comment on this post