I'm trying to invalidate a Panel from a callback. This is the code I have:
Code Block
Public Class Form1
Public Delegate Sub PanelInvalidateDelegate(ByVal R As Rectangle)
Public Sub SubOnCallbackThread()
Dim PID As PanelInvalidateDelegate = AddressOf Panel2.Invalidate
PID.Invoke( New Rectangle(0, 0, 42, 256))
End Sub
End Class
The Sub "SubOnCallbackThread" executes without error but the panel never gets invalidated and paints. What am I doing wrong? | | JohnWein Wednesday, October 10, 2007 9:17 PM | I think you may be confusing two meanings of Invoke. The one you're using is the Invoke method of the delegate, which runs it on a new thread pool thread. What I think you're trying to do, however, is call Invalidate using the thread that created the panel. Instead of
PID.Invoke(New Rectangle(0, 0, 42, 256))
try doing (sorry, I don't know VB syntax -- the second argument should be an array of Object containing a single element--the rectangle)
Panel2.Invoke(PID, New Object() { New Rectangle(0, 0, 42, 256) } )
This will wait for the message loop thread to execute the method pointed to by PID (Panel2.Invalidate in this case).
If you actually did want it to run asynchronously, which is what [delegate].Invoke is used for, use Panel2.BeginInvoke instead.
This might all be stuff that I'm incorrectly bringing from C#, though...
| | sirjis Wednesday, October 10, 2007 10:28 PM | I think you may be confusing two meanings of Invoke. The one you're using is the Invoke method of the delegate, which runs it on a new thread pool thread. What I think you're trying to do, however, is call Invalidate using the thread that created the panel. Instead of
PID.Invoke(New Rectangle(0, 0, 42, 256))
try doing (sorry, I don't know VB syntax -- the second argument should be an array of Object containing a single element--the rectangle)
Panel2.Invoke(PID, New Object() { New Rectangle(0, 0, 42, 256) } )
This will wait for the message loop thread to execute the method pointed to by PID (Panel2.Invalidate in this case).
If you actually did want it to run asynchronously, which is what [delegate].Invoke is used for, use Panel2.BeginInvoke instead.
This might all be stuff that I'm incorrectly bringing from C#, though...
| | sirjis Wednesday, October 10, 2007 10:28 PM | sirjis: Thanks for your response. You are right I'm confused. You are also right in that I am trying to invalidate the panel using the thread that created the panel. I'll try your suggestions. I'm sure they will get me past my current impast. | | JohnWein Wednesday, October 10, 2007 10:43 PM | I chaned the invoke line to:
Code Block
Panel2.Invoke(PID, New Rectangle(0, 0, 42, 256))
and I get an error:
"Invoke or BeginInvoke cannot be called on a control until the window handle has been created."
But that can't be the true description of the error, because the sub can't be called until after the window is shown and the window definitely has a handle.
| | JohnWein Thursday, October 11, 2007 6:39 AM | There's something wrong with your panel. In your original code, you should have gotten an IllegalOperationException if the panel had a handle. If you created it dynamically, be sure to add it to the form's Controls collection. You don't have to use the panel's Invoke() method, Me.Invoke() will work too. | | nobugz Thursday, October 11, 2007 11:46 AM | I've got more problems than Panel.Invalidate. I have a C implementation of a TV Automatic Volume Control that I'm trying to transfer to VB.Net. Some things are easier to do in native C than they are in .Net. It's a learning experience. Now I'm hung up on a Wave call and this isn't the forum for that.
sirjis:
Thanks for pointing me in the right direction for invoke. I have a better feeling for delegates now. | | JohnWein Thursday, October 11, 2007 2:21 PM |
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