CODEWITHSUNDEEP
c#asp.netdynamicasp.net-3.5page-lifecycle
Volearix
Volearix

Reputation: 1593

Creating dynamic asp controls

Down and to the point question. I am having a miserable time with some dynamically created buttons. They do not want to fire the Click event I have setup for them. A paraphrase of my code is below. Could anyone provide some insight as to why my dynamic controls do not work?

protected void Page_Load(object sender, EventArgs e)
{
    CreateButton();
}
private void CreateButton()
{
    Button btn = new Button();
    btn.ID = "Button1";
    btn.Click += Button1_Click;

    panel1.Controls.Add(btn);
}

protected void Button1_Click(object sender, EventArgs e)
{
    // Do stuff here.
    // Debugger never makes it to this point.
}

I have this current functionality. It needs to be able to graphically reorder, remove and add items.

enter image description here

Upvotes: 0

Views: 61

Answers (2)

the berserker
the berserker

Reputation: 1594

Page_Load is probably already too late to do that and in ASP.NET lifecycle there is a CreateChildControls method that you should use to create controls dynamically.

Frequent problems with dynamically generated controls and events not being fired are (Edit: the 2nd bullet is probably your issue, since you mention reordering of controls; also as you submitted the picture, repeater seems better idea, as it was proposed by Servy):

  • if you forget to assign the ID to the control, ASP.NET can generate different ID to the control on the client and the handlers will not be invoked on server (you have that covered)
  • if the hierarchy of the controls changes on postback, ASP.NET will not be able to find a control in the control tree and therefore not invoke the handler again (controls on server are matched by index instead by name!). You can compare the page trace of control tree between 1st render of the page and postback. You should assure that the control tree is not different between postbacks (e.g. you should not skip adding controls to the page on postback, but rather include them in the control tree, but not display them).

Upvotes: 0

Servy
Servy

Reputation: 203804

Just...don't use dynamic ASP controls. Ever. They're super hard to work with, and there are superior alternatives.

If you want to create a dynamic number of controls based on some data that you have use a Repeater, or, if you want to create a table of data specifically, a DataGrid. These have sensible behaviors and are far easier to work with.

If you have content that you want to optionally render, for example a single fixed button that may or may not need to be shown, then define that control in markup and use the Visible property to determine if it is actually send to the end user.

As for why it doesn't work, ASP has many steps in a page's lifecycle. One of the early steps is to initialize it's view of the page with all of the items on it. At a later point in time the post back data is inspected, any events triggered find their corresponding control in the view of the page, and then run the corresponding handlers for that event. In your case you're creating the control and adding the handlers after the request's "page view" has already been finalized. The code didn't see your button, or any handlers for it, so it didn't have any handlers to run.

This is all complicated further if the creation of your dynamic controls are dependent on information being posted back from the user (which does in fact appear to be the case here). If you create the controls early enough in the lifecycle for them to be able to fire events, then the information that you need to get from what the user has just done hasn't yet been populated into their corresponding ASP constructs. You end up being forced to construct the dynamic objects before you actually have access to the information to construct them.

Upvotes: 1

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