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Putting a background image on a ListView (Delphi 7)
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Question:
I need to display a bitmap as a background picture in a TListView control and it seems not to work.I send a message LVM_SETBKIMAGE with the handle to a TLVBkImage, but no success.
Answer:
The code is ok but you need to change the handling of the WM_ERASEBKGND message by either traditional subclassing or - more Delphi style - defining your own TMyListView derived from TListView as shown in the example. Then change the declaration of your listview control from TListView to TMyListView (both in your DFM and in your PAS file) and it will work.Notes:
- I noticed that I had to provide a full path to the image file. Just the file name (even though it was located in the application directory) did not work.
- Benoît Thonnart, a reader of this page wrote me that after he added uses ComObj; to his (version of this) code, it worked.
You can download a complete demo project that will compile under Delphi 7 (and since it has the constant definitions integrated, also under Delphi 5 and Delphi 6).
TListviewBackgroundImage.zip(240 kB)
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type
TMyListView = class(TListView)
protected
procedure WndProc(var Message: TMessage);
override;
end;
procedure TMyListView.WndProc(var Message: TMessage);
begin
if Message.Msg = WM_ERASEBKGND then
DefaultHandler(Message)
else
inherited WndProc(Message);
end;
procedure TForm1.LVBGImage;
var
BKimg : TLVBKIMAGE;
begin
FillChar(BKimg, SizeOf(BKimg), 0);
BKimg.ulFlags := LVBKIF_SOURCE_URL or LVBKIF_STYLE_TILE;
BKimg.pszImage := PChar('c:\windows\angler.bmp');
BKimg.xOffsetPercent := 0;
BKimg.yOffsetPercent := 0;
CoInitialize(nil);
SendMessage(ListView1.Handle, LVM_SETTEXTBKCOLOR, 0, integer(CLR_NONE));
SendMessage(ListView1.Handle, LVM_SETBKIMAGE, 0, integer(@BKimg));
CoUninitialize;
end;
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