Question

For our project, we’ve written a WinForms UserControl for graphing.

We’re seeing some strange behavior when our control is sited in a TabControl – our control continuously fires Paint events, even when there is absolutely no activity by the user.

We only see this in the TabControl. When we site our control in other containers such as Forms or Splitters, Paint is only fired when you’d expect e.g. when the control is first displayed, etc.

Can anyone suggest why this might be happening?

Here’s a stack trace from a breakpoint in our control’s Paint handler, if that’s any help. Our control is BaseGraphXY, which is sited on a TabControl, which is sited on some nested SplitContainers. Sorry about the formatting – couldn’t get the SO editor to stop wrapping, for some reason.

OverlordFrontEnd.exe!OverlordFrontEnd.MainForm.graphControl_Paint(object sender =  BI_BaseGraphXY.BaseGraphXY}, System.Windows.Forms.PaintEventArgs e = {ClipRectangle = {X=0,Y=0,Width=1031,Height=408}}) Line 422 C#
System.Windows.Forms.dll!System.Windows.Forms.Control.OnPaint(System.Windows.Forms.PaintEventArgs e) + 0x73 bytes   
BI_AppCore.dll!BI_BaseGraphXY.BaseGraphXY.OnPaint(System.Windows.Forms.PaintEventArgs e = {ClipRectangle = {X=0,Y=0,Width=1031,Height=408}}) Line 377 + 0xb bytes   C#
System.Windows.Forms.dll!System.Windows.Forms.Control.PaintTransparentBackground(System.Windows.Forms.PaintEventArgs e, System.Drawing.Rectangle rectangle, System.Drawing.Region transparentRegion = null) + 0x16c bytes   
System.Windows.Forms.dll!System.Windows.Forms.Control.PaintBackground(System.Windows.Forms.PaintEventArgs e = {ClipRectangle = {X=0,Y=0,Width=1029,Height=406}}, System.Drawing.Rectangle rectangle, System.Drawing.Color backColor, System.Drawing.Point scrollOffset) + 0xbc bytes    
System.Windows.Forms.dll!System.Windows.Forms.Control.PaintBackground(System.Windows.Forms.PaintEventArgs e, System.Drawing.Rectangle rectangle) + 0x63 bytes   
System.Windows.Forms.dll!System.Windows.Forms.Control.OnPaintBackground(System.Windows.Forms.PaintEventArgs pevent) + 0x59 bytes    
System.Windows.Forms.dll!System.Windows.Forms.Control.PaintWithErrorHandling(System.Windows.Forms.PaintEventArgs e = {ClipRectangle = {X=0,Y=0,Width=1029,Height=406}}, short layer, bool disposeEventArgs = false) + 0x74 bytes    
System.Windows.Forms.dll!System.Windows.Forms.Control.WmPaint(ref System.Windows.Forms.Message m) + 0x1ba bytes 
System.Windows.Forms.dll!System.Windows.Forms.Control.WndProc(ref System.Windows.Forms.Message m) + 0x33e bytes 
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.OnMessage(ref System.Windows.Forms.Message m) + 0x10 bytes    
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.WndProc(ref System.Windows.Forms.Message m) + 0x31 bytes  
System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.Callback(System.IntPtr hWnd, int msg = 15, System.IntPtr wparam, System.IntPtr lparam) + 0x5a bytes  
[Native to Managed Transition]  
[Managed to Native Transition]  
System.Windows.Forms.dll!System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(int dwComponentID, int reason = -1, int pvLoopData = 0) + 0x24e bytes 
System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(int reason = -1, System.Windows.Forms.ApplicationContext context = {Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.WinFormsAppContext}) + 0x177 bytes    
System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoop(int reason, System.Windows.Forms.ApplicationContext context) + 0x61 bytes    
System.Windows.Forms.dll!System.Windows.Forms.Application.Run(System.Windows.Forms.ApplicationContext context) + 0x18 bytes 
Microsoft.VisualBasic.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun() + 0x81 bytes    
Microsoft.VisualBasic.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel() + 0xef bytes   
Microsoft.VisualBasic.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(string[] commandLine) + 0x2c0 bytes 
OverlordFrontEnd.exe!OverlordFrontEnd.Program.Main() Line 36 + 0x10 bytes   C#
[Native to Managed Transition]  
[Managed to Native Transition]  
mscorlib.dll!System.AppDomain.ExecuteAssembly(string assemblyFile, System.Security.Policy.Evidence assemblySecurity, string[] args) + 0x3a bytes    
Microsoft.VisualStudio.HostingProcess.Utilities.dll!Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() + 0x2b bytes  
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart_Context(object state) + 0x66 bytes   
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) + 0x6f bytes    
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart() + 0x44 bytes   

Answer 1

My co-worker has found a workaround for the problem:

The problem with the graph control was that the BackColor property was defaulting to System.Drawing.Color.Transparent. This caused a kind of a “feedback loop” of messages. I guess that it is supposed to work this way? Anway, I changed the constructor to use System.Drawing.SystemColors.ControlLightLight as the default BackColor property. This seems to suppress the extra graph painting.