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How to block input to the system until released

The Windows API BlockInput function prevents all input to the system, making it appear locked up until released. Declare the function as:

function BlockInput(fBlockInput: Boolean): DWORD; stdcall;
  external 'user32.dll';

Usage: Set to True to "lock-up" and False to "unlock" input devices.

The following code locks up input for 2 seconds:

procedure TForm1.Button1Click(Sender: TObject);
begin
  BlockInput(True);
  Label1.Caption := 'Blocked';
  Application.ProcessMessages;
  Sleep(2000);
  BlockInput(False);
  Label1.Caption := 'Unblocked';
end;

Example code added by Peter Johnson

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