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Item Type: NewsGroup Date Entered: 3/4/2005 11:41:55 PM Date Modified: Subscribers: 0 Subscribe Alert
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michaelpietsch
Asp.Net User
adding controls in response to PostBacks3/4/2005 11:41:55 PM

0/0

I am building yet another tree control - mostly for the fun of it. Plus I was unable to locate a _really_ simple one. Mine simply takes a non-normalized table for input and does nothing fancy at all...

However, nodes can be expanded and collapsed. Nodes are represented by LinkButtons which add or remove the node from a list of expanded nodes, represented by an ArrayList currently stored in the ViewState. I could also move it to the session-object.

Problem: At what point do I build my tree and instantiate my new LinkButtons?

I cannot do it before PostBackEvents have been processed , because what controls are added depends on the the LinkButton that was clicked.

I cannot do it in the PreRender phase either, because event-handling code has already been created at that point and my new LinkButtons will not be hooked up to events.

How would you go about this?

I can see two solutions:
1. Always create the entire tree and set the Visibility-property accordingly.
2. Resorting to handing info over through the querystring.

Any comment would be appreciated. I am still trying to figure ASP.NET out.....

Michael
miguelcastro67
Asp.Net User
Re: adding controls in response to PostBacks3/9/2005 3:34:42 PM

0/0

You should be using ViewState to persist the current state of the tree (basically what nodes are openned and closed). Then it should all be recreated in the CreateChildControls method (if this is a composite control). It is not good practice to try to access IsPostBack from a webcontrol and you should definately not be trying to access QueryString. It can be done, but you will be very tightly coupling your control to the page/site.
Good luck,
Miguel Castro
www.dotnetdude.com
michaelpietsch
Asp.Net User
Re: adding controls in response to PostBacks3/12/2005 9:25:48 PM

0/0

Hi Miguel,

I'm still totally lost. Or even more so.

I keep on running into situations where I need to add controls in response to postback-events.

According to the trace, events fire in the following order:
1. Page_Init
2. Page_Load
3. [PostBackEvents]
4. Page_PreRender

When Postback-Events are handled, it is already too late to add controls programatically. That is understandable, since controls have to exist in order to fire events. Therefore controls have to be added during Page_Init and Page_Load BEFORE PostBackEvents are fired. And that in turn means that controls cannot be added in response to PostBack, right?

I hate using the querystring, but it seems that is the only thing that can be influenced on the page (through simple links) and that's available during Page_Init and Page_Load.

Michael
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