TListView scrolling bug when using VCL Styles - Delphi XE8 - delphi

Question

I've tried to set TListView control's direction to RTL by following function:
procedure RTL_LV(lv:TListView);
const
LVM_FIRST = $1000;
LVM_GETHEADER = LVM_FIRST + 31;
var
header: THandle;
begin
header:= SendMessage (lv.Handle, LVM_GETHEADER, 0, 0);
SetWindowLong (header, GWL_EXSTYLE,
GetWindowLong (header, GWL_EXSTYLE) or
WS_EX_LAYOUTRTL or WS_EX_NOINHERITLAYOUT);
SetWindowLong (lv.Handle, GWL_EXSTYLE,
GetWindowLong (lv.Handle, GWL_EXSTYLE) or
WS_EX_LAYOUTRTL or WS_EX_NOINHERITLAYOUT);
lv.invalidate;
end;
But I have two problems as follows when the project uses VCL Styles:
1: Vertical scrollbar not appearing without clicking on it.
2: When i change the size of the ListView columns and the horizontal scrollbar is clicked, the following error message is displayed:
Exception source: Vcl.ComCtrls.TListViewStyleHook.WMMouseMove
procedure TListViewStyleHook.WMMouseMove(var Message: TWMMouse);
var
SF: TScrollInfo;
SPos: Integer;
R: TRect;
begin
if VertSliderState = tsThumbBtnVertPressed then
begin
SF.fMask := SIF_ALL;
SF.cbSize := SizeOf(SF);
GetScrollInfo(Handle, SB_VERT, SF);
ScrollPos := ScrollPos + (SF.nMax - SF.nMin) * ((Mouse.CursorPos.Y - PrevScrollPos) / VertTrackRect.Height);
PrevScrollPos := Mouse.CursorPos.Y;
if Control is TCustomListView then
begin
PostMessage(Handle, WM_VSCROLL, Integer(SmallPoint(SB_THUMBTRACK, Round(ScrollPos))), 0);
if TCustomListView(Control).ViewStyle = vsReport then
begin
if (Abs(ScrollPos - ListPos) >= 1) or
((ScrollPos = SF.nMin) and (ListPos <> ScrollPos)) or
((ScrollPos = SF.nMax) and (ListPos <> ScrollPos)) then
begin
if TCustomListView(Control).GroupView then
begin
SPos := Round(ScrollPos - ListPos);
if SF.nPos + SPos < 0 then SPos := -SF.nPos;
end
else
begin
ListView_GetItemRect(Handle, 0, R, LVIR_BOUNDS);
SPos := Round((ScrollPos - ListPos) * R.Height);
end;
ListView_Scroll(Handle, 0, SPos);
ListPos := ScrollPos;
end;
end
else
begin
if Abs(ScrollPos - ListPos) >= 1 then
begin
ListView_Scroll(Handle, 0, Round((ScrollPos - ListPos)));
ListPos := ScrollPos;
end;
end;
end
else
PostMessage(Handle, WM_VSCROLL, Integer(SmallPoint(SB_THUMBPOSITION, Round(ScrollPos))), 0);
PaintScroll;
Handled := True;
Exit;
end;
if HorzSliderState = tsThumbBtnHorzPressed then
begin
SF.fMask := SIF_ALL;
SF.cbSize := SizeOf(SF);
GeTScrollInfo(Handle, SB_HORZ, SF);
ScrollPos := ScrollPos + (SF.nMax - SF.nMin) * ((Mouse.CursorPos.X - PrevScrollPos) / HorzTrackRect.Width);
if ScrollPos < SF.nMin then
ScrollPos := SF.nMin;
if ScrollPos > SF.nMax then
ScrollPos := SF.nMax;
PrevScrollPos := Mouse.CursorPos.X;
if Control is TCustomListView then
begin
if TCustomListView(Control).ViewStyle = vsReport then
begin
if Abs(ScrollPos - ListPos) >= 1 then
begin
ListView_Scroll(Handle, Round((ScrollPos - ListPos)), 0);
ListPos := ScrollPos;
end;
end
else
begin
if Abs(ScrollPos - ListPos) >= 0.5 then
begin
ListView_Scroll(Handle, Round((ScrollPos - ListPos)), 0);
ListPos := ScrollPos;
end;
end;
end
else
PostMessage(Handle, WM_HSCROLL, Integer(SmallPoint(SB_THUMBPOSITION, Round(ScrollPos))), 0);
PaintScroll;
Handled := True;
Exit;
end;
if (HorzSliderState <> tsThumbBtnHorzPressed) and (HorzSliderState = tsThumbBtnHorzHot) then
begin
HorzSliderState := tsThumbBtnHorzNormal;
PaintScroll;
end;
if (VertSliderState <> tsThumbBtnVertPressed) and (VertSliderState = tsThumbBtnVertHot) then
begin
VertSliderState := tsThumbBtnVertNormal;
PaintScroll;
end;
if (HorzUpState <> tsArrowBtnLeftPressed) and (HorzUpState = tsArrowBtnLeftHot) then
begin
HorzUpState := tsArrowBtnLeftNormal;
PaintScroll;
end;
if (HorzDownState <> tsArrowBtnRightPressed) and (HorzDownState =tsArrowBtnRightHot) then
begin
HorzDownState := tsArrowBtnRightNormal;
PaintScroll;
end;
if (VertUpState <> tsArrowBtnUpPressed) and (VertUpState = tsArrowBtnUpHot) then
begin
VertUpState := tsArrowBtnUpNormal;
PaintScroll;
end;
if (VertDownState <> tsArrowBtnDownPressed) and (VertDownState = tsArrowBtnDownHot) then
begin
VertDownState := tsArrowBtnDownNormal;
PaintScroll;
end;
CallDefaultProc(TMessage(Message));
if LeftButtonDown then
PaintScroll;
Handled := True;
end;
How should this problems be solved?
Thanks.

Answer 1

There are multiple problems with your approach. The quick answer is:
Do not do this. Instead, set the controls's BiDiMode property to bdRightToLeft. Unless I am missing something, that will get you the behavior you need and I tested it now, there are no problems with scrolling with themes this way.
There are two big problems with the way you are tying to do this:
You can't guarantee the control will keep the settings you are forcing into it. The first time the VCL needs to recreate the Window for the control, your settings will be obliterated.
You are assuming that the VCL doesn't need to account for this setting in some way. Clearly it does, because you are getting bad behavior when trying to undercut the VCL and send the style directly to the Window. If you really want to directly control the window style, you need to create your own descendant of the control class and handle everything related in the proper places-- you can't just pick any old time you want to change the control to RTL with a Windows API call (rather than the control's properties) and expect that the control will continue to work properly.