wittrup
wittrup

Reputation: 1565

Preserving negative/reverse string selection after updating TMemo text in Delphi?

In Delphi I'm having trouble preserving the SelStart and SelLength in a Memo that updates it text every 5 seconds when the selection is negative/reverse.

With negative/reverse selection I mean that I have started the selection somewhere and while holding shift pressed the left arrow key some times.

Code:

var
  caret: TPoint;
  sel_start, sel_length: Integer;
begin
  sel_start := Memo1.SelStart;    //          =  5
  sel_length := Memo1.SelLength;  //          = 10
  caret := Memo1.CaretPos;        // caret.x  = 15

  //'adi and bl' selected
  caret.x := sel_start;
  Memo1.Lines.Clear;
  Memo1.Lines.Add('laditadi and blah blah');
  Memo1.SelStart := sel_start;
  Memo1.SelLength := sel_length;

  Memo1.CaretPos := caret;
end;

The thing is that setting the SelLength seems to actually move the caret. And setting the caret after setting SelLength makes SelLength := 0;. Since the text keeps changing I can't use TMemo.SelText / TMemo.SetSelText before and after.

I can't find a way to preserve the caret pos...any clues?

Upvotes: 2

Views: 841

Answers (1)

bummi
bummi

Reputation: 27377

If sel_start has the same value as characterposition of the Caret, selection will be reversed by setting selstart to selstart+sellength and setting sellength to -sellength.

procedure TForm1.Button1Click(Sender: TObject);
var
  caret: TPoint;
  sel_start, sel_length,CharFromPos: Integer;
begin
  Memo1.SetFocus;
  GetCaretPos(Caret);
  CharFromPos := SendMessage(Memo1.Handle, EM_CHARFROMPOS, 0 ,Caret.Y*$FFFF + Caret.X) AND $FFFF;
  sel_start := Memo1.SelStart;    //          =  5
  sel_length := Memo1.SelLength;  //          = 10

  Memo1.Lines.Clear;
  Memo1.Lines.Add('laditadi and blah blah'#13#10'laditadi and blah blah');
  if  sel_start<>CharFromPos then
      begin
       Memo1.SelStart := sel_start;
       Memo1.SelLength := sel_length;
      end
    else
      begin
       Memo1.SelStart := sel_start + sel_length;
       Memo1.SelLength := - sel_length;
      end;

end;
procedure TForm1.Timer1Timer(Sender: TObject);
var
 p:Tpoint;
 b:Boolean;
 CharFromPos:Integer;
begin
   b := GetCaretPos(p);
   CharFromPos := SendMessage(Memo1.Handle, EM_CHARFROMPOS, 0 ,p.Y*$FFFF + p.X) AND $FFFF;
   Caption := Format('SelStart %d CharFromPos %d',[Memo1.SelStart,CharFromPos])
end;

Upvotes: 2

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