Custom control, postback and master pages

[madmital]

Hi.

I have a custom control that inherits from TextBox and implements ICallbackEventHandler.
The control is kind of an extended ajax autocomplete/suggestions one.

Aside from the Text property of the Textbox I have extended the control with a Value property.
The idea is that a Hiddenfield control is assigned a value by javascript upon selected a autocomplete suggestion on the client side, which can then be read server side on postback.

I add the "extra" HiddenField by overriding the control's OnInit event

private HiddenField hf = new HiddenField();
protected override void OnInit(EventArgs e) {
 hf.ID = base.UniqueID + "_hf";
 this.Controls.Add(hf);
 base.OnInit(e);
}

The control also extends a Value property

public string Value {
 get { return hf.Value; }
 set { hf.Value = value; }
}

And in the control's Render method (aside from all the other stuff) I do

protected override void Render(System.Web.UI.HtmlTextWriter writer) {
... 
 base.Render(writer);
 hf.RenderControl(writer);
...
}

And then my problem:

On postbacks I am able to retrieve the control's Value property.
That is...for example, from a buttons click event I am able get the controls Value (assigned by javascript client side). No problem.

But when I try to do the exact same with on a webform with a master page the control's Value property is never populated on postback.
It's almost like the viewstate isn't restored or something.

Anywayz; I'm puzzled as to why the things works fine on a "normal" webform but fails when using a master page.
Why the difference.
Everything else works fine.

Any help or ideas would be greatly appreciated.

[kvprajapati]

Did you read this?
1. http://msdn.microsoft.com/en-us/library/zt27tfhy.aspx
2. Adding AJAX functionality to ASP.NET Controls.

[madmital]

Hi, and thanks for your reply.

And no...I didn't read through the articles you mention.
This is my first go at a server control, so I probably should have.
I'm gonna start with the sections on state management.

[madmital]

Hrmm...

It seems overriding the SaveViewState method and manually retrieving the HiddenField's value does the trick.

protected override object SaveViewState() {
	this.hf.Value = ((HiddenField)base.Controls[0]).Value;
	object baseState = base.SaveViewState();
	return baseState;
}

Now I only need to understand why the above is necessary... :)