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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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LockWindowUpdate function (Windows) and some OldNewThing thoughts

Posted by jpluimers on 2021/02/02

If you ever think about using [WayBack] LockWindowUpdate function (Windows), then read these first:

TL;DR:

Do not use LockWindowUpdate as the limitation is system wide: Only one Window in the system can be used for LockWindowUpdate.

Use WM_SETREDRAW if you can as LockWindowUpdate “should only to be called to disable drawing in the window beneath the cursor during a drag and drop operation”: there is only one locked window at a time: There can be only one drag/drop operation active at a time, since there is only one mouse.

Instead of LockWindowUpdate(hwnd)
Use SendMessage(hwnd, WM_SETREDRAW, FALSE, 0) or
SetWindowRedraw(hwnd, FALSE)
Instead of LockWindowUpdate(NULL)
Use SendMessage(hwnd, WM_SETREDRAW, TRUE, 0) or
SetWindowRedraw(hwnd, TRUE)

Prototype

BOOL LockWindowUpdate(
  _In_ HWND hWndLock
);

Oh, and it’s not called LockWindowUpdate everywhere: [WayBackSetting a Visual Studio breakpoint on a Win32 API function in user32.dll – The Entrian Solutions Blog.

–jeroen

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