Controlling a variable numbers of controls dynamically added to a user control

 Ok, thinking caps on people, this has been causing me grief for a couple of days now.

I have an .aspx page which contains various user controls housed in an Accordion control from the Ajax Toolkit and lots of UpdatePanels, these user controls all interact with each other through the parent page, e.g clicking buttons in one control effects visibility of other controls.

Two of these controls contain just a series of ImageButtons. In the first of these controls the ImageButtons are generated in the page_load method and added to a panel using Panel.Controls.Add(ImageButtonControl), the number of ImageButtons and their ImageUrl properties are read from a database and depend on one of the user's profile parameters. The ImageButton.Click method is assigned as follows,

//In the control creation code
imgbutton.Click += new ImageClickEventHandler(ImageButton_Click);
//later the method is declared
public ImageClickEventHandler ImageClick;

protected void ImageButton_Click(object sender, ImageClickEventArgs e)
if (ImageClick != null)
HiddenField1.Value = ((ImageButton)sender).ID;
ImageClick(this, e);


Then on the parent .aspx page

protected void Page_Load(object sender, EventArgs e)
this.Repair_main1.ImageClick += new ImageClickEventHandler(GroupImageButtonClick);

public void GroupImageButtonClick(object sender, ImageClickEventArgs e)
HiddenField hidden1 = (HiddenField)Repair_main1.FindControl("HiddenField1");
HiddenField hidden2 = (HiddenField)RepairGroup1.FindControl("HiddenField2");

The HiddenFields are used to pass the ID of the ImageButton clicked in the first control into the second control. This ID then determines how many and which ImageButtons are displayed in the second control. This is where the problems start. Since the ImageButtons in the first control cause an autopostback event, the code that is executed by the ImageButton.Click method from the first control is executed after the Page_Load method of the second control, or so is my understanding of the .NET page life cycle.

If the ID that I need to determine how many and which ImageButtons to display in the second control is being assigned in the PostBackEvent stage then I have to put my ImageButton creation code in the Page_PreRender method (the code is almost the same structure as in the first control). But in the Page_PreRender method EventHandlers can not be assigned, so none of my ImageButtons have .Click methods. I can not created the ImageButtons in the Page_Load method because I do not have the ID of the button that was clicked in the first control yet.

I have tried giving the second control a publicly accessible property for the ID and assigning it in the click method in the parent page, but that didn't work. The big problem is that I always need to create my imagebuttons before the PreRender stage but the postback action of the imagebuttons means that any code to pass the ID through that I execute in the click method of the first control is executed just before the PreRender stage of the second control.

Is there any way to generate this second control with working imagebutton events or am I being dense and going about it all wrong? I do not want to have to put all the buttons on the page with visible properties set as I don't want to  limit the number of images that can be displayed. If there is a way of making a selection in the first control and passing the ID through to the second control before the page_load stage then that would be perfect.

Many thanks, Lex


1/30/2008 12:13:43 PM 93655 articles. 5 followers. Follow

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Have you tried to add the ImageButtons during the Init phase instead of the page_load phase?  When they are added that early in the cycle they should be available to event handlers and the page_load of other user controls.  Often this is done in the CreateChildControls method of the initalization phase.

Hope this helps.

John Stockton
RIA Developer at Ascentium
Co-Author of Silverlight 2 in Action

1/30/2008 1:12:48 PM

thats part of the problem, I don't know how many controls i need to add to the page at the Page_Init stage. The event timeline is like this

 1. ImageButton clicked on first control

2. Postback occurs

3. second control page_init and page_load

4. Now the method associated with my from the first control runs and the ID is passed over to the second control

5. SQL query to database to find out how many images are associated with the ID

6. Controls are added to page

i can't do anything in the second control until the ID has been assigned (step 4), by which point its too late in the page life cycle to assign eventhandlers to my new imagebuttons

1/30/2008 1:33:24 PM

You may want to try to hijack the life-cycle by not waiting for the page_load event and event handlers to do the processing but read the requisite values directly from the Request.Form collection during init.  I'm just guessing here but this may let you do what you are trying before the lifecycle would normally permit.

John Stockton
RIA Developer at Ascentium
Co-Author of Silverlight 2 in Action

1/30/2008 2:09:11 PM

 Thanks John,

I was able to find the ID of the button being pressed inside the Request.Form collection, the code is a little messy but it works nicely. Found this link which has useful info on extracting stuff from Request.Form 

 Many thanks, Lex

1/30/2008 4:17:16 PM

Cool, I'm glad I was able to point you in the right direction.  You may also want to go ahead and mark this as answered so others know it has been rexolved.

John Stockton
RIA Developer at Ascentium
Co-Author of Silverlight 2 in Action

1/30/2008 4:25:51 PM

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