Adding multiple clientside event handlers to ASP.NET controls

I often come across scenario which requires assigning multiple javascript handlers to ASP.NET controls, via code. Let me elaborate the scenario:

  • You need to hook up multiple javascript handlers to some ASP.NET control (example, to ‘onclick’ event of a TextBox).
  • This has to be done from server side code (datagrid,datalist or any such dynamic scenario).
  • The javascript handlers are ‘functions’ that accept a number of parameters.

In this article, I will show how to do this with ‘jQuery’. As many of you might be knowing, there is talk of Visual Studio supporting jQuery in future. This makes ‘jQuery’ the ideal candidate. All one needs to do is download a javascript file from their site and reference it in the *.aspx page. I have written two javascript functions which I will demonstrate attaching to client-side ‘click’ event of ASP.NET textbox.

<script src="jquery-1.2.6.min.js" type="text/javascript"></script>
<script type="text/javascript">
function Handler1(p1){alert('Handler1 called.['+p1+']');}
function Handler2(p1,p2){alert('Handler2 called.['+p1+' '+p2+']');}

Now, in the code-behind of the *.aspx file, code looks like this:

protected override void OnPreRender(EventArgs e)
       StringBuilder sb = new StringBuilder();
       string functionCall = "$('#{0}').bind('{1}', function(){{ {2} }});\n"; 
       sb.Append(" $(window).bind('load',function(){\n");
       sb.Append(string.Format(functionCall string functionCall = "$('#{0}').bind('{1}', function(){{ {2} }});\n"; all, TextBox1.ClientID, "click", "Handler2('param1','param2')"));
       sb.Append(string.Format(functionCall, TextBox2.ClientID, "click", "Handler1('param1')"));
       sb.Append(string.Format(functionCall, TextBox2.ClientID, "click", "Handler2('param1','param2')"));
       sb.Append ("});");

The above code does two things:

  • Attaches a handler to the window.load event.
  • Adds handlers for client-side ‘click’ event of TextBox1 and TextBox2. This assignment is done inside body of ‘window.load’ handler.

Again to make things more clear, let us see what is being rendered on client-side:

  <script type="text/javascript">
$('#TextBox1').bind('click', function(){ Handler1('param1') });
$('#TextBox1').bind('click', function(){ Handler2('param1','param2') });
$('#TextBox2').bind('click', function(){ Handler1('param1') });
$('#TextBox2').bind('click', function(){ Handler2('param1','param2') });

The ‘$()’ is the famous dollar function. The notation $(‘#TextBox1’) is roughly eqvivalent to saying document.getElementById(‘TextBox1’). To further understand the code check out tutorials for jQuery. As always, let me know your suggestions and comments.