Exception thrown by System.Drawing

[Tyler Foreman]

Hello,

I had an earlier post regarding a strange exception I
(thought) I was getting in my windows form. I have since
been able to trace the problem to a picturebox control on
my form. I can reproduce the exception consistently, but
it seems to be timing dependent. Here is what happens:

I have a subform that I open, load an image from a file
into my PictureBox, take some user input, then I hide the
form. The last thing I do before I Hide the form is
release the Image's hold on the file by using Dispose().
This is where the problem occurs. The code is as follows:

'Release image resource
Try
PictureBox1.Ima ge.Dispose()
Catch tobj As Exception
MsgBox(tobj.Mes sage)
End Try

Try
Application.DoE vents()
Catch e
MsgBox(e.Messag e)
End Try

Me.Hide()

The exception is caught in the second Try. The message
says:
System.Argument Exception occured in
System.Windows. Forms.dll
Additional Information: Invalid Parameter Used.

Inspection of the exception shows that it is thrown by
System.Drawing. Inspection of the Stack Trace shows that
it is thrown from the "get_Width" method within the dll.
It appears to stem from when the PictureBox is redrawing
itself.

So here is my theory: It seems that there is some sort
of race condition between when I call Image.Dispose() and
when the Image is repainting itself that is causing this
problem. I haven't yet been able to verify this. Any
ideas? I would appreciate any help or input on this
problem.

Thanks alot. I have included the Stack Trace below.

Tyler Foreman

StackTrace" at System.Drawing. Image.get_Width ()
at System.Drawing. Image.get_Size( )
at System.Windows. Forms.PictureBo x.get_ImageRect angle()
at System.Windows. Forms.PictureBo x.OnPaint
(PaintEventArgs pe)
at System.Windows. Forms.Control.P aintWithErrorHa ndling
(PaintEventArgs e, Int16 layer, Boolean disposeEventArg s)
at System.Windows. Forms.Control.W mPaint(Message& m)
at System.Windows. Forms.Control.W ndProc(Message& m)
at System.Windows. Forms.ControlNa tiveWindow.OnMe ssage
(Message& m)
at System.Windows. Forms.ControlNa tiveWindow.WndP roc
(Message& m)
at System.Windows. Forms.NativeWin dow.DebuggableC allback
(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at
System.Windows. Forms.UnsafeNat iveMethods.Disp atchMessageW
(MSG& msg)
at
System.Windows. Forms.Component Manager.System. Windows.Forms
..UnsafeNativeM ethods+IMsoComp onentManager.FP ushMessageLoop
(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
at
System.Windows. Forms.ThreadCon text.RunMessage LoopInner
(Int32 reason, ApplicationCont ext context)
at System.Windows. Forms.ThreadCon text.RunMessage Loop
(Int32 reason, ApplicationCont ext context)
at System.Windows. Forms.Applicati on.DoEvents()
at MYAPP.Form2.Sav eEvent_Click(Ob ject eventSender,
EventArgs eventArgs)

[Fergus Cooney]

Hi Tyl;er,

PictureBox1.Ima ge.Dispose() will dispose of the underlying resource used
by the Image, ie the internal BitMap. PictureBox1.Ima ge is still there,
however, so when PictureBox1_Pai nt occurs, it says "Ah here's an Image to
draw" but then there's no BitMap inside. :-(

You need:
PictureBox1.Ima ge.Dispose()
PictureBox1.Ima ge = Nothing

Then System.Windows. Forms.PictureBo x.OnPaint won't bother trying to call
get_ImageRectan gle().

Regards,
Fergus

[Tyler Foreman]

Thanks Fergus! That did the trick!

Cheers,
Tyler Foreman

-----Original Message-----
Hi Tyl;er,

PictureBox1.Ima ge.Dispose() will dispose of the underlying resource usedby the Image, ie the internal BitMap. PictureBox1.Ima ge is still there,however, so when PictureBox1_Pai nt occurs, it says "Ah here's an Image todraw" but then there's no BitMap inside. :-(

You need:
PictureBox1.Ima ge.Dispose()
PictureBox1.Ima ge = Nothing

Then System.Windows. Forms.PictureBo x.OnPaint won't bother trying to callget_ImageRecta ngle().

Regards,
Fergus
.