problems about invoke method ?

Chanh Quang Nguyen

13y1.9k

I've viewed this link http://msdn.microsoft.com/en-us/library/zyzhdc6b.aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-1 .It talks about Invode method.And I haven't got clear about some points of this.As refered in the article : "The Invoke method searches up the control's parent chain until it finds a control or form that has a window handle if the current control's underlying window handle does not exist yet. If no appropriate handle can be found, the Invoke method will throw an exception. Exceptions that are raised during the call will be propagated back to the caller."

I don't understand some definitions such as "the control's parent chain", "a window handle", "if the current control's underlying window handle", so I hope someone gives me explainations about these ones !

2 Replies

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Vulpes13y ago
Accepted answer
Well, the Control.Invoke method calls a delegate on the thread that owns the control's underlying window handle i.e. the thread on which the control was created.

A window handle is a number which uniquely identifies a control, created by a given process, to the operating system and there's often a short delay before the handle is created and the control becomes visible.

Suppose the Invoke method is called on a control which doesn't yet have a window handle.

The code will then look up the control's 'inheritance tree' to see if it can find a control which does have a window handle. For example, if Invoke were called on a custom TextBox object which didn't yet have a handle, the code would look to see if the parent object (a standard TextBox) did have a handle.

If no ancestor object had a handle, then an exception would be thrown. However, if a handle can be found, then the Invoke method can determine the thread which owns that handle (sometimes the current thread) and invoke the delegate on that thread.
Chanh Quang Nguyen13y ago
thanks, Vulpes ! now i understand more clearly although not completely ! ^~^