TScrollBox with dynamically created Memos issue [duplicate] - delphi

Question

I have a TScrollBox that has a RichEdit that is bigger than the scrollbox, so both side scrollbars appear in the scrollbox. Then I have a function DoTask that calls RichEdit.SetFocus.
When I scroll down to where I want to see part of the text control, and then call DoTask, the ScrollBox will automatically scroll to the top of the RichEdit. How can I avoid that?

Answer 1

As you wish, here are some suggestions:
Override SetFocusedControl in the form:
function TForm1.SetFocusedControl(Control: TWinControl): Boolean;
begin
if Control = RichEdit then
Result := True
else
Result := inherited SetFocusedControl(Control);
end;
Or:
type
TCustomMemoAccess = class(TCustomMemo);
function TForm1.SetFocusedControl(Control: TWinControl): Boolean;
var
Memo: TCustomMemoAccess;
Scroller: TScrollingWinControl;
Pt: TPoint;
begin
Result := inherited SetFocusedControl(Control);
if (Control is TCustomMemo) and (Control.Parent <> nil) and
(Control.Parent is TScrollingWinControl) then
begin
Memo := TCustomMemoAccess(Control);
Scroller := TScrollingWinControl(Memo.Parent);
SendMessage(Memo.Handle, EM_POSFROMCHAR, Integer(#Pt), Memo.SelStart);
Scroller.VertScrollBar.Position := Scroller.VertScrollBar.Position +
Memo.Top + Pt.Y;
end;
end;
Interpose TScrollBox:
type
TScrollBox = class(Forms.TScrollBox)
protected
procedure AutoScrollInView(AControl: TControl); override;
end;
procedure TScrollBox.AutoScrollInView(AControl: TControl);
begin
if not (AControl is TCustomMemo) then
inherited AutoScrollInView(AControl);
end;
Or:
procedure TScrollBox.AutoScrollInView(AControl: TControl);
begin
if (AControl.Top > VertScrollBar.Position + ClientHeight) xor
(AControl.Top + AControl.Height < VertScrollBar.Position) then
inherited AutoScrollInView(AControl);
end;
Or use any creative combination of all of the above. How and when you like it to be scrolled only you know.

Answer 2

the simpliest solution would be
var a, b : Integer;
begin
a := ScrollBox1.VertScrollBar.Position;
b := ScrollBox1.HorzScrollBar.Position;
richEdit1.SetFocus;
ScrollBox1.VertScrollBar.Position:=a ;
ScrollBox1.HorzScrollBar.Position:=b ;
end;

Answer 3

Without hacking into VCL/deriving custom components there's only one solution - TForm.SetFocusedControl override + re-setting the positions of scrollbars as said above. One thing I added is disabling/enabling window redraw to avoid ugly jumps.
Here's my final snippet:
sbContainer is TScrollBox and NoScrCtrl is a control laying inside it which gets focus but we don't want it to be scrolled-in-view.
function TForm1.SetFocusedControl(Control: TWinControl): Boolean;
var hpos, vpos: integer;
begin
if Control = NoScrCtrl then
begin
sbContainer.Perform(WM_SETREDRAW, WPARAM(False), 0);
hpos := sbContainer.HorzScrollBar.Position;
vpos := sbContainer.VertScrollBar.Position;
Result := inherited SetFocusedControl(Control);
sbContainer.HorzScrollBar.Position := hpos;
sbContainer.VertScrollBar.Position := vpos;
sbContainer.Perform(WM_SETREDRAW, WPARAM(True), 0);
sbContainer.Refresh;
end
else
Result := inherited SetFocusedControl(Control);
end;

Answer 4

To disable scroll-into-view behavior from my main form, I used this solution: (C++Builder)
bool __fastcall TMainForm::SetFocusedControl(TWinControl *Control) {
LockWindowUpdate(Handle);
int vpos = VertScrollBar->Position;
int hpos = HorzScrollBar->Position;
bool result = TForm::SetFocusedControl(Control);
if (VertScrollBar->Position != vpos) {
VertScrollBar->Position = vpos;
}
if (HorzScrollBar->Position != hpos) {
HorzScrollBar->Position = hpos;
}
LockWindowUpdate(0);
return result;
}