How to Draw a Label in ListView client area - delphi

Question

When there is no data to show in ListView, it is better to show message as "no data is changed now", which should be drawed in a TLabel.
How to draw a TLabel in the ListView client area?

Answer 1

You don't need a TLabel for that.
On Vista and later, you can subclass the ListView to handle the LVN_GETEMPTYMARKUP notification.
uses
..., CommCtrl;
private
PrevWndProc: TWndMethod;
procedure TMyForm.FormCreate(Sender: TObject);
begin
PrevWndProc := ListView.WndProc;
ListView.WndProc := ListViewWndProc;
end;
procedure TMyForm.ListViewWndProc(var Message: TMessage);
begin
if Message.Msg = CN_NOTIFY then
begin
if TWMNotifyLV(Message).NMHdr.code = LVN_GETEMPTYMARKUP then
begin
with PNMLVEmptyMarkup(TWMNotifyLV(Message).NMHdr)^ do
begin
dwFlags := EMF_CENTERED;
StrLCopy(szMarkup, 'My message here', L_MAX_URL_LENGTH);
end;
Message.Result := 1;
Exit;
end;
end;
PrevWndProc(Message);
end;
The downside is you have little control over where the text appears (only whether it is left-justified or centered) or how it is formatted, and you cannot change the text dynamically (you would have to add at least one item and then remove it to trigger a new notification).
On earlier versions, or if you need more control over the text position/format/behavior, you can use the ListView's OnCustomDraw event instead. You can draw whatever you want on the ListView's Canvas within the area designated by a TRect provided by the event. If needed, you can use ListView_GetHeader() to determine if the ListView's column headers are visible, and if so then use GetWindowRect() to get the header's height so you can subtract it from the top of the TRect before drawing.
For example:
procedure TMyForm.ListViewCustomDraw(Sender: TCustomListView; const ARect: TRect; var DefaultDraw: Boolean);
var
R, Temp: TRect;
Wnd: HWND;
begin
if Sender.Items.Count <= 0 then
begin
R := ARect;
Wnd := ListView_GetHeader(Sender.Handle);
if Wnd <> 0 then
begin
GetWindowRect(Wnd, #Temp);
R.Top := R.Top + (Temp.Bottom-Temp.Top);
end;
R.Top := R.Top + 10;
DrawText(Sender.Canvas.Handle, 'My message here', -1, #R, DT_CENTER or DT_SINGLELINE);
end;
end;