ASP.NET 2.0 - Adding controls at runtime?

[wbjohnson]

Hey guys i have a small problem.... im sure you can help I have a new project, with 2 buttons on Button1 and Button2... The code behind button1 is simple: Textbox t = new Textbox(); t.Text = "hello world!"; form1.Controls.Add(t); when i click Button1 - wow! it adds the control! No problem, i noticed that i can click the button as many times as i want and only 1 textbox ever appears. so Click button1, then click Button2 - POW! its vanised! Whats the correct method of keeping a control "alive" on a page (as well as preserving any events it has?) Cheers Will

[Member 96]

I'm not an expert by any means on this, however I believe it might have to do with the point at the page event lifecycle when you create the controls. From what I understand any dynamic controls should be created very early in the page lifecycle and I use the Page_Init event always for dynamic controls and have had no problems with them. However I did have problems when trying to create them on page_load.

[Guffa]

Every postback produces a completely new Page object, so to make a dynamically created control stay on the page, you have to recreate it on every postback.

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[Guffa]

You shouldn't have any problem with adding controls in Page_Load. The Page_Init didn't event exist in framework 1.x.

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[Member 96]

Right, although they do recommend Page_Init and some 3rd party components I'm using require that as well because if you create them any later you don't get their values properly from viewstate. http://support.microsoft.com/kb/317515

[Guffa]

Yes, for some reason that is not revealed, it says that Page_Init is the best place for it, but it also says: "When you create dynamic controls on a Web Form, you must create the controls and add them to the controls collection in either the Page_Init event handler or the Page_Load event handler." So, either works for dynamic controls. If some controls need to be created in Page_Init, it's because how they are built, not because you create them dynamically.

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[Member 96]

No, I looked a little deeper into it and you *must* create them in Page_Init if you want their viewstate to be restored properly because the event that loads viewstate into the controls occurs before Page_Load but after Page_Init.

[Guffa]

Are you sure? Has this changed between framework 1.1 and framework 2.0? Otherwise it would be impossible to use dynamic controls in framework 1.1, as there is no Page_Init.

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[Member 96]

Maybe it's changed, not sure, I never used .net 1.x with asp.net, but that's been my experience with asp.net 2.0 and that's what Microsoft detailed on the page I found at the time when I looked it up on MSDN. I use dynamic controls for a custom fields section on many of my forms and if I don't create them in page init then I can't retrieve their values later on in the page lifecycle.