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I have a problem with the text editors in Delphi XE2 when a VCL style is applied. If I have 2 TMemo controls (Memo1 and Memo2) placed on a form and Memo1 is partially behind Memo2, then the scollbars of Memo1 are painted over Memo2.

I tried to create a style hook inherited from TScrollingStyleHook, but I didn't find any way to fix the problem. Does anybody have an idea on how this bug could be fixed?

BTW: I tested it in Delphi XE5 too and it behaves in the same way.

Here is the source code for the .dfm and .pas files:

DFM:

object Form1: TForm1 Left = 0 Top = 0 Caption = 'Form1' ClientHeight = 282 ClientWidth = 418 Color = clBtnFace Font.Charset = DEFAULT_CHARSET Font.Color = clWindowText Font.Height = -11 Font.Name = 'Tahoma' Font.Style = [] OldCreateOrder = False PixelsPerInch = 96 TextHeight = 13 object Memo1: TMemo Left = 120 Top = 80 Width = 185 Height = 89 Lines.Strings = ( 'Memo1') ScrollBars = ssBoth TabOrder = 0 end object Memo2: TMemo Left = 160 Top = 128 Width = 185 Height = 89 Lines.Strings = ( 'Memo2') ScrollBars = ssBoth TabOrder = 1 end end

PAS:

unit Unit1; interface uses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls; type TForm1 = class(TForm) Memo1: TMemo; Memo2: TMemo; private { Private declarations } public { Public declarations } end; var Form1: TForm1; implementation {$R *.dfm} end.
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  • Can you include a image of the issue? Commented Oct 17, 2013 at 16:57
  • I am a new member of this website and I am not allowed to add images to the post, but I added the .pas and .dfm code to the description. Commented Oct 18, 2013 at 11:05

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The Vcl Style Engine does not support correctly the scrollbar , in memo , the scrollbar is created from TScrollWindow class that is inherited from TWinControl class . the standard scrollbar (without vcl style) is painted as a part of memo . When using the vcl style the scrollbar of memo become a top window , and that's what cause the previous problems. if you look at the TScrollingStyleHook.UpdateScroll event , you can find that the style engine use SetWindowPos that bring the scrollbar to the top of others controls in order to show the scrollbar .

SetWindowPos(FVertScrollWnd.Handle, HWND_TOP, Control.Left + Left, Control.Top + Top, Right - Left, Bottom - Top, SWP_SHOWWINDOW);

if you want to fix this issue you need to paint the scrollbar inside the TMemo class , in the WM_NCPAINT message .

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Thanks S.Mahdi! You are right. I modified WM_NCPAINT and it seems that this is the way, but it requires other changes too, because the scrollbars are not painted entirely correct.

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