Preventing the user from selecting text in a Memo control

Setting Enabled to False has some undesirable side-effects...

Preventing the user from selecting text in a Memo control



The easiest way would be to set the Enabled property of the Memo (or Edit) control to False so that the control cannot receive events. This drawback to this method is the user won't be able to scroll the text and the disabled text looks bad.



In order to prevent the user from writing in the memo, we set its ReadOnly property to True.



To prevent the user from selecting text with the mouse, we generate the handler of the MouseMove event of the control and write the following code:



procedure TForm1.Memo1MouseMove(Sender: TObject;

   Shift: TShiftState; X, Y: Integer);

  begin

    if ssLeft in Shift then

      Memo1.SelLength := 0;

  end;


In order to prevent the user from performing a selection using the keyboard, we generate the handlers of the KeyDown and KeyUp events, assigning the OnKeyDown and OnKeyUp properties to the same procedure:





procedure TForm1.Memo1KeyDownUp(Sender: TObject;

    var Key: Word; Shift: TShiftState);

  begin

    if (ssShift in Shift) and (Key in [VK_LEFT, VK_RIGHT, VK_UP,

        VK_DOWN, VK_PRIOR, VK_NEXT, VK_HOME, VK_END]) then

      Key := 0;

  end;


You can find the full source code of this article in the archive that accompanies the Pascal Newsletter #25

 

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