[SOLVED] ListView flicker

[Zaxxon]

when you resize a listview there is a lot of flickering

I've tried to overrride the WM_ERASEBKGND message by

Code: Pascal  [Select][+][-]

1. procedure TForm1.ListViewWndProc(var Msg:TMessage);
2. begin
3.   if Msg.msg=WM_ERASEBKGND then begin
4.     Msg.Result:=1;
5.   end
6.   else begin
7.     Self.OldListViewWndProc(Msg);  
8.   end;
9. end;
10.  

and that removed the flicker, but that caused other issues. Is there a better way of getting rid of the flicker?
Or is the flicker a bug?

I'm using lazarus 1.6 / FPC 3.0.0 in win 7 64 bit.

[Michl]

Or is the flicker a bug?

Yes, it was a bug and should be fixed in Lazarus Trunk (http://bugs.freepascal.org/view.php?id=30076).

You can try the patch in the bug report, if it works for you too?!

[balazsszekely]

@Michl
I work with lazarus trunk, but the project still flickers a lot.

@Zaxxon
I see you're under windows. Please test the attached project:

Code: Pascal  [Select][+][-]

1. uses windows;
2. //...
3. var
4.   PrevWndProc: WNDPROC;
5.  
6. function WndCallback(AHWND: HWND; uMsg: UINT; wParam: WParam; lParam: LParam): LRESULT; stdcall;
7. begin
8.   case uMsg of
9.     WM_ENTERSIZEMOVE: begin
10.       LockWindowUpdate(Form1.ListView1.Handle);
11.       Form1.ListView1.Align := alNone;
12.       Form1.ListView1.Width := 10000;
13.       Form1.ListView1.Height := 10000;
14.       Form1.DisableAlign;
15.       LockWindowUpdate(0);
16.     end;
17.     WM_EXITSIZEMOVE: begin
18.       LockWindowUpdate(Form1.ListView1.Handle);
19.       Form1.ListView1.Align := alClient;
20.       Form1.EnableAlign;
21.       LockWindowUpdate(0);
22.     end;
23.   end;
24.   Result := CallWindowProc(PrevWndProc, Ahwnd, uMsg, WParam, LParam);
25. end;
26.  
27. procedure TForm1.FormCreate(Sender: TObject);
28. var I:Integer;
29.     LI:TListItem;
30.     B:Boolean;
31. begin
32.   Self.ListView1.DoubleBuffered:=True;
33.   Self.ListView1.Font.Size:=11;
34.   B:=True;
35.   for I:=0 to 30 do begin
36.     LI:=Self.ListView1.Items.Add;
37.     LI.Caption:=IntToStr(Random(1000000));
38.  
39.     if B then LI.SubItems.Add('Yes')
40.     else LI.SubItems.Add('No');
41.  
42.     B:=not B;
43.   end;
44.   PrevWndProc := Windows.WNDPROC(SetWindowLongPtr(Form1.Handle, GWL_WNDPROC, PtrInt(@WndCallback)));
45. end;
46.  
47. procedure TForm1.ListView1CustomDrawItem(Sender: TCustomListView;
48.   Item: TListItem; State: TCustomDrawState; var DefaultDraw: Boolean);
49. begin
50.   if Item.SubItems[0]='Yes' then Self.ListView1.Canvas.Brush.Color:=clBlue
51.   else Self.ListView1.Canvas.Brush.Color:=clGreen;
52. end;

[Zaxxon]

GetMem, your version removed the flicker, Thanks!

[serbod]

Another way - use VirtualTreeView ( http://wiki.freepascal.org/VirtualTreeview ). It not flickers, can be used as list and have many useful features.

[Zaxxon]

A little update.

GetMem : your solution don't work well if you have other aligned components, such as panels.
So I contiuned on my first solution and used yours partially. I simply fill the areas that is not painted in the
WM_ERASEBKGND message. It's not perfect, but it will work for now. 

I attached the new version.

[balazsszekely]

@Zaxxon
In theory, when you resize or move a form, the controls should not be updated until the operation is completed. I think the easiest solution, which works in all cases(it might not be the most elegant though) is this:

Code: Pascal  [Select][+][-]

1. function WndCallback(AHWND: HWND; uMsg: UINT; wParam: WParam; lParam: LParam): LRESULT; stdcall;
2. begin
3.   case uMsg of
4.     WM_ENTERSIZEMOVE: Form1.DisableAlign;
5.     WM_EXITSIZEMOVE: Form1.EnableAlign;
6.   end;
7.   Result := CallWindowProc(PrevWndProc, Ahwnd, uMsg, WParam, LParam);
8. end;

PS: Thanks for your feedback and your example.