Double Buffering question

ricecake

I am trying to implement double buffering in a form, and I am getting a crash. I have a fix for the crash but I don't know if it's "correct". To enable double buffering, I call this function from the form's constructor:

System::Void enable_double_buffering()
{
using System::Windows::Forms::ControlStyles;

SetStyle(static\_cast<ControlStyles>(ControlStyles::DoubleBuffer |
                                    ControlStyles::UserPaint |
                                    ControlStyles::AllPaintingInWmPaint),
         true);
UpdateStyles();

}

My Paint handler looks like this:

System::Void PlotDisplayWindow_Paint(System::Object* /*sender*/, System::Windows::Forms::PaintEventArgs* e)
{
using System::Drawing::Graphics;

Graphics\* g = e->Graphics;
// draw an image
g->Dispose();

}

If I do not enable double buffering, then it works fine, but with flickering. With double buffering, I get the following exception:

************** Exception Text **************
System.ArgumentException: Invalid parameter used.
at System.Drawing.Graphics.EndContainer(GraphicsContainer container)
at System.Windows.Forms.DibGraphicsBufferManager.ReleaseBuffer(GraphicsBuffer buffer)
at System.Windows.Forms.GraphicsBuffer.Dispose()
at System.Windows.Forms.Control.WmPaint(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
at System.Windows.Forms.ContainerControl.WndProc(Message& m)
at System.Windows.Forms.Form.WndProc(Message& m)
at System.Windows.Forms.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

If I comment out the g->Dispose(); line in the Paint handler, then I do not get the crash. Is it correct/acceptable not to dispose of the Graphics object after painting? -- Marcus Kwok

leppie

ricecake wrote:

If I comment out the g->Dispose(); line in the Paint handler, then I do not get the crash. Is it correct/acceptable not to dispose of the Graphics object after painting?

General rule is you should not be calling Dispose on objects that you didnt create :)**

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**

ricecake

leppie wrote:

General rule is you should not be calling Dispose on objects that you didnt create

Yeah, looking back on it I think the call to Dispose() was an artifact of when I tried to use threads and CreateGraphics(). -- Marcus Kwok