How Can I Efficiently Suspend and Resume Painting for a .NET Control and Its Children?

Optimizing .NET Control Repainting with WM_SETREDRAW

.NET developers often need to temporarily halt repainting within a control and its children during extensive updates. While SuspendLayout and ResumeLayout manage layout, they don't fully suppress redrawing.

The WM_SETREDRAW Solution

The WM_SETREDRAW message, sent to the control's window handle, provides a robust solution. A boolean parameter controls redrawing: false disables, and true enables it.

Implementing SuspendDrawing and ResumeDrawing Methods

This streamlined class encapsulates the functionality:

public static class ControlPainting
{
    [DllImport("user32.dll")]
    public static extern int SendMessage(IntPtr hWnd, int wMsg, bool wParam, int lParam);

    private const int WM_SETREDRAW = 11;

    public static void SuspendPainting(Control parent)
    {
        SendMessage(parent.Handle, WM_SETREDRAW, false, 0);
    }

    public static void ResumePainting(Control parent)
    {
        SendMessage(parent.Handle, WM_SETREDRAW, true, 0);
        parent.Refresh();
    }
}

Usage Example

To prevent repainting:

ControlPainting.SuspendPainting(myControl);
// ... perform modifications ...
ControlPainting.ResumePainting(myControl);

Further Reading

For more in-depth information, consult these resources:

• C# Jitter
• Suspending Layouts

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