Question

I have a control which I have to make large modifications to. I’d like to completely prevent it from redrawing while I do that – SuspendLayout and ResumeLayout aren’t enough. How do I suspend painting for a control and its children?

Answer 1

At my previous job, we struggled with getting our rich UI app to paint instantly and smoothly. We were using standard .Net controls, custom controls and devexpress controls.

After a lot of googling and reflector usage, I came across the WM_SETREDRAW win32 message. This really stops controls drawing whilst you update them and can be applied, IIRC to the parent/containing panel.

This is a very very simple class demonstrating how to use this message:

class DrawingControl {     [DllImport("user32.dll")]     public static extern int SendMessage(IntPtr hWnd, Int32 wMsg, bool wParam, Int32 lParam);      private const int WM_SETREDRAW = 11;           public static void SuspendDrawing( Control parent )     {         SendMessage(parent.Handle, WM_SETREDRAW, false, 0);     }      public static void ResumeDrawing( Control parent )     {         SendMessage(parent.Handle, WM_SETREDRAW, true, 0);         parent.Refresh();     } } 

There are fuller discussions on this – google for C# and WM_SETREDRAW, e.g.

C# Jitter

Suspending Layouts

And to whom it may concern, this is a similar example in VB:

Public Module Extensions     <DllImport("user32.dll")>     Private Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As Boolean, ByVal lParam As IntPtr) As Integer     End Function      Private Const WM_SETREDRAW As Integer = 11      ' Extension methods for Control     <Extension()>     Public Sub ResumeDrawing(ByVal Target As Control, ByVal Redraw As Boolean)         SendMessage(Target.Handle, WM_SETREDRAW, True, IntPtr.Zero)         If Redraw Then             Target.Refresh()         End If     End Sub      <Extension()>     Public Sub SuspendDrawing(ByVal Target As Control)         SendMessage(Target.Handle, WM_SETREDRAW, False, IntPtr.Zero)     End Sub      <Extension()>     Public Sub ResumeDrawing(ByVal Target As Control)         ResumeDrawing(Target, True)     End Sub End Module