Delphi - Get and Set Scrollbar Position of a ListView

Question

It might seem like a silly & simple question, and yet, I've been unable to find a satisfying answer. Basically, I have a TListview (style = vsReport) with data. Sometimes, I have to update it, and therefore, I have to clear the listview and fill it again with the updated data.

However, when I do that, the scrollbar position is reseted to 0. I would like to be able to get the scrollbar position before the clearing and set it back to what it was before. If the updated data has the exact same amount of rows as the old data, I need the scrollbar to be at the exact same position as before; if not, I just need it to be more-or-less at the same place as before.

Seems easy, right? Yet, all I've found are hacks or tweaks with TopItem and MakeVisible. Is there any appropriate method to do that?

Thanks!

Answer 1

Save the top item before clearing,

FSaveTop := ListView1.TopItem;

After updating, scroll the listview so that the saved top item's 'y' position will be 0 (+ header height):

var
  R: TRect;
begin
  if Assigned(FSaveTop) then begin
    // account for header height
    GetWindowRect(ListView_GetHeader(ListView1.Handle), R);
    ListView1.Scroll(0, FSaveTop.Position.Y - (R.Bottom - R.Top));
  end;
end;

Actually, since you're re-populating the listview, you have to devise a mechanism to find which item you want to be at the top instead of saving a reference to it.

If you don't like modifying scroll position through 'top item', since functions like SetScrollInfo, SetScrollPos won't update the client area of the control, you can use GetScrollInfo to get the 'nPos' of a TScrollInfo before clearing the list, and then send that many WM_VSCROLL messages with 'SB_LINEDOWN` after populating.

Save scroll position:

var
  FPos: Integer;
  SInfo: TScrollInfo;
begin
  SInfo.cbSize := SizeOf(SInfo);
  SInfo.fMask := SIF_ALL;
  GetScrollInfo(ListView1.Handle, SB_VERT, SInfo);
  FPos := SInfo.nPos;
  ...

After populating, scroll (assuming scroll position is 0):

var
  R: TRect;
begin
  ...
  R := ListView1.Items[0].DisplayRect(drBounds);
  ListView1.Scroll(0, FPos * (R.Bottom - R.Top));

or,

var
  i: Integer;
begin
  ...
  for i := 1 to FPos do
    SendMessage(ListView1.Handle, WM_VSCROLL, SB_LINEDOWN, 0);

Answer 2

type
  TForm1 = class(TForm)
    ListView1: TListView;
    Timer1: TTimer;
    Timer2: TTimer;
    procedure FormCreate(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
    procedure Timer2Timer(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
    pb:array [0..20] of Tprogressbar;
    i:integer;
      mintop,spacetop,readtop:integer;
    implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);


begin

mintop:=19;
spacetop:=14;
for i:=0 to 20 do
begin
listview1.AddItem('Item no'+inttostr(i),nil);
pb[i]:=Tprogressbar.create(self);
pb[i].Parent:=listview1;
pb[i].width:=120;
pb[i].height:=14;
pb[i].top:=mintop+i*spacetop;
pb[i].position:=i*5;
pb[i].Left:=listview1.Column[0].Width;



end;


end;

procedure TForm1.Timer1Timer(Sender: TObject);
var
  z,FPos: Integer;
  SInfo: TScrollInfo;
begin
  SInfo.cbSize := SizeOf(SInfo);
  SInfo.fMask := SIF_ALL;
  GetScrollInfo(ListView1.Handle, SB_VERT, SInfo);
  FPos := SInfo.nPos;
  form1.caption:='FPOS='+inttostr(fpos);
if fpos>0 then
begin
for z:=0 to 11 do
begin
pb[z+fpos-1].Top:=mintop+z*spacetop;
form1.caption:=form1.caption+' Z='+inttostr(z)+' !';
     end;
     end;

 end;
procedure TForm1.Timer2Timer(Sender: TObject);
var x:integer;
begin
  for  x:=0 to 20 do
  begin
  pb[x].Position:=Pb[x].position+1;
  end;


end;

end.


/// Code by BRTH1 - Simao Coelho - Portugal