How to implement a Virtual ImageList for TListView? [SOLVED]

[fournoas]

I need to display a large number of images in the ListView. I cannot load all these images into the ImageList at once, as it would consume too much memory.

I attempted to implement a virtual ImageList, only to find that the methods of TCustomImageList are non-virtual and cannot be modified to alter its default behavior.

Is there any way to dynamically load images in a ListView?

[fournoas]

Mybe the Virtual ImageList is a bad idea.

I implemented the desired functionality using CustomDrawItem.

[vfclists]

Will you show us what the code looks like?

[fournoas]

Will you show us what the code looks like?

my pleasure

1. Set ListView1.OnCustomDrawItem event handle

Code: Pascal  [Select][+][-]

1. procedure TMainForm.ListViewCustomDrawItem(Sender: TCustomListView; Item: TListItem; State: TCustomDrawState; var DefaultDraw: Boolean);
2. begin
3.   if State = [] then Exit;
4.   case ListView.ViewStyle of
5.     vsIcon: LoadLargeIcon(Sender, Item);
6.     vsSmallIcon: LoadSmallIcon(Sender, Item);
7.     vsReport: LoadSmallIcon(Sender, Item);
8.   end;
9. end;
10.  

2. Draw picture

Code: Pascal  [Select][+][-]

1. procedure LoadSmallIcon(ListView: TCustomListView; Item: TListItem);
2. var
3.   IconRect: TRect;
4.   Picture: TPicture;
5. begin
6.   IconRect := Item.DisplayRect(drIcon);
7.   Picture := TPicture.Create;
8.   Picture.LoadFromFile('D:\small.jpg');
9.   ListView.Canvas.Draw(IconRect.Left, IconRect.Top, FilterPicture(Picture, Item.Selected, ListView.Focused).Graphic);
10.   Picture.Free;
11. end;
12.  
13. procedure LoadLargeIcon(ListView: TCustomListView; Item: TListItem);
14. var
15.   IconRect: TRect;
16.   Picture: TPicture;
17. begin
18.   IconRect := Item.DisplayRect(drIcon);
19.   Picture := TPicture.Create;
20.   Picture.LoadFromFile('D:\large.jpg');
21.   ListView.Canvas.Draw(
22.     IconRect.Left + (IconRect.Width - Picture.Width) div 2,
23.     IconRect.Top + (IconRect.Height - Picture.Height),
24.     FilterPicture(Picture, Item.Selected, ListView.Focused).Graphic);
25.   Picture.Free;
26. end;
27.  

3. Processing image highlight effects

Code: Pascal  [Select][+][-]

1. function FilterPicture(Picture: TPicture; Selected, Focused: boolean): TPicture;
2. var
3.   PixelColor: TColor;
4.   X, Y: Integer;
5. begin
6.   Result := Picture;
7.   if not Selected then Exit;
8.   for X := 0 to Picture.Width - 1 do
9.   begin
10.     for Y := 0 to Picture.Height - 1 do
11.     begin
12.       PixelColor := Picture.Bitmap.Canvas.Pixels[X, Y];
13.       Picture.Bitmap.Canvas.Pixels[X, Y] :=
14.         specialize IfThen<TColor>(Focused, DecColor(PixelColor, $30), IncColor(PixelColor, $30));
15.     end;
16.   end;
17. end;
18.  

It should be noted that the code has the following issues:
1. The picture is not scaled
2. The image highlight effect does not look very good
3. Tested only on Windows

[wp]

Is there also text in these items? Not 100% sure, but don't you have to output this, too? Or, since DefaultDraw should be true, doesn't the ListView itself draw the text, but overwrites the icon because it does not know about it?

[fournoas]

Is there also text in these items? Not 100% sure, but don't you have to output this, too? Or, since DefaultDraw should be true, doesn't the ListView itself draw the text, but overwrites the icon because it does not know about it?

ListView.OwnDraw := False;

ListView will render text and draw icons.