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  1. PO
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    <p>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.</p> <p>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.</p> <p>This is a very very simple class demonstrating how to use this message:</p> <pre class="lang-cs prettyprint-override"><code>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(); } } </code></pre> <p>There are fuller discussions on this - google for C# and WM_SETREDRAW, e.g.</p> <p><a href="https://web.archive.org/web/20160324214157/http://blog.bee-eee.com/2008/04/18/c-getting-rid-of-the-jitter/" rel="noreferrer">C# Jitter</a></p> <p><a href="http://www.c-sharpcorner.com/Forums/ShowMessages.aspx?ThreadID=52" rel="noreferrer">Suspending Layouts</a></p> <p>And to whom it may concern, this is similar example in VB:</p> <pre class="lang-vb prettyprint-override"><code>Public Module Extensions &lt;DllImport("user32.dll")&gt; 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 &lt;Extension()&gt; Public Sub ResumeDrawing(ByVal Target As Control, ByVal Redraw As Boolean) SendMessage(Target.Handle, WM_SETREDRAW, True, 0) If Redraw Then Target.Refresh() End If End Sub &lt;Extension()&gt; Public Sub SuspendDrawing(ByVal Target As Control) SendMessage(Target.Handle, WM_SETREDRAW, False, 0) End Sub &lt;Extension()&gt; Public Sub ResumeDrawing(ByVal Target As Control) ResumeDrawing(Target, True) End Sub End Module </code></pre>
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    1. POHow do I suspend painting for a control and its children?
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    1. POHow do I suspend painting for a control and its children?
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    1. COWhat a great answer and a tremendous help! I made SuspendDrawing and ResumeDrawing extension methods for the Control class, so I can call them for any control in any context.
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      1. USZach Johnson
    2. COHad a tree-like control that would only refresh a node properly on rearranging its children if you collapsed then expanded it, which led to ugly flickering. This worked perfectly to get around it. Thanks! (Amusingly enough, the control already imported SendMessage, *and* defined WM_SETREDRAW, but didn't actually use it for anything. Now it does.)
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    3. COThis isn't particularly useful. This is exactly what the `Control` base class for *all* of the WinForms controls *already does* for the `BeginUpdate` and `EndUpdate` methods. Sending the message yourself is no better than using those methods to do the heavy lifting for you, and certainly can't produce different results.
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      1. USCody Gray
 

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