Limiting the type of child controls a custom control can have

 How does one do this? I'm looking to create a web control that functions similar to the DropDownList control, in that it would only allow certain types of child controls inside of it(ex: DropDownList only allows ListItems in it).

 Am I missing something glaringly obvious about this problem? I can't seem to find any information on how to do it.

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rossisdead
12/8/2008 11:58:21 PM
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Those aren't child controls.  It is a custom syntax for setting the Property "Items" of the the drop down list.

The inner  contents of a control can either be properites or custom controls.  For instance if you put something inside the tags of a System.Web.UI.Literal control, it is going to set the "Text" property of the Literal control.  If you put something inside of a System.Web.UI.Panel control it is going to treat those as child controls.

When you create a custom control you can specify if the inner contents of the control should be considered properties or childcontrols.  The default is dependant on which base class you inherit from (ie: Control, or CompositeControl, or WebControl)  In all cases you can overide the default.   You do this by decorating your control with some specific attributes.

 Specifically check out the ParseChildrenAttribute, the PersistChildrenAttribute, the DefaultPropertyAttribute.

 You need to decide a couple things for sure.

Do you want the inner contents of your control to specifcy the value of a single property, the values for a collection property (like the drop down list), or to be actuall child controls.

If you really want them to be Child Controls, then thats fine, however you can't easily modify the control to only accept certain child controls and not others.  

If you really want to do that, look into control builders, which are basically a way to fully customize how the page parser looks at your control.

Here is a page to get you started http://msdn.microsoft.com/en-us/library/ms178658.aspx  and http://msdn.microsoft.com/en-us/library/ms178654.aspx and  http://msdn.microsoft.com/en-us/library/ms178648.aspx

In fact everything in this section is probably useful to you: http://msdn.microsoft.com/en-us/library/zt27tfhy.aspx

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viscious
12/9/2008 1:12:09 AM
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