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Change History: This post was updated on July 5, 2005. See Update at bottom.
You can't add two identical events to the same Html control. For example, if you have a button with an onclick event, and you add another onclick at the server, the second event will overwrite the first. This becomes a problem if you need to add an event to some variable control, but you don't know what events that control already has. However, .Net provides a way to handle this.
We can:
The following code snippets this. This first block shows a simple JavaScript (with a parameter) being called by a button's onclick event.
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This snippet shows the server code to check if an onclick event already exists, and add a new wrapper if needed. Note that it persists the onclick values in viewstate to ensure that the wrapper function doesn't wrap itself upon postback. For example, if the first onclick event called DoStuff1(), and we wanted to dynamically add a new onclick function DoStuff2(), we could create a wrapper function Wrapper1() that called both functions, and was called from the onclick. Wrapper1() becomes the new value of the button's onclick.
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While this approach is tedious, it lets you dynamically add an event to a control without overwriting that control's existing event. This is useful when making your own custom controls that integrate with existing Html controls already on the page.
UPDATE July 5, 2005
Since writing this post, I've come across a cleaner technique. You can run multiple JavaScripts simply by listing them in the onclick event:
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Therefore we can simplify our codebehind. This has two main changes: (1) It modifies OriginalJSFunction to append the ";" to the end of a non-function, (2) It then always adds an onclick method, as opposed to checking if there already exists an onclick method.
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That method you used to run multiple events under one onClick saved my
life. I spent forever trying to figure out a way to make it do multiple
things, like display a new picture, and erase an old one at the same time.
Thanx a ton
How can i append an existing attribute.
For example:
cmd.Attributes.add("onClick","alert('Something.');");
Then how can i add another attribute appending to the existing onClick
Attribute.
Somthing like
cmd.Attribute.Append("onClick","alert('Another thing')");
Which i know is wrong.. but i hope u got my point.
Any one knows it. Say my thanks to him before he tells me :-)
er_sudhir_yadav@gmail.com
Sudhir Yadav
Sorry the mail id was incorrect
Let me correct it, its:
er.sudhir.yadav@gmail.com
Sudhir Yadav
Hey Sudhir, you can "append" by (1) getting the original event's method,
and then doing a string append to that. I mention this in the blog snippet:
string s = this.Button1.Attributes;
if (!Page.IsPostBack)
OriginalJSFunction = s;
this.Button1.Attributes.Add("onclick",OriginalJSFunction + ";DoStuff2()");
I am trying to run a routine which will insert an image and remove the text
at the same time...
