List box item height

[tailkinker]

So the TListbox.ItemHeight documentation states that this is not implemented.  How can I determine the height of each item in the TListBox?  (I want to make the TListBox automatically scale with items, so I never need to worry about scroll bars.)

[wp]

Set the Style to lbOwnerDrawFixed, and you can set ItemHeight to any value. Or set Style to lbOwnerDrawVariable, and you can define an individual height for each line by implementing a handler for the OnMeasureItem event.

[tailkinker]

The problem is that I want to determine the height as set by the font being used, rather than trying to guess.  (Which is what I am currently doing.) 

[wp]

The following code yields the same line height as that of a listbox with lbStandard style. --> Just measure the height of some text in the listbox (you could use the Listbox.canvas directly, but since that is not always available I used an auxiliary bitmap):

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormCreate(Sender: TObject);
2. var
3.   bmp: TBitmap;
4.   h: Integer;
5. begin
6.   bmp := TBitmap.Create;
7.   try
8.     bmp.SetSize(1, 1);
9.     bmp.Canvas.Font := Listbox2.Font;
10.     h := bmp.Canvas.TextHeight('Tg');
11.   finally
12.     bmp.Free;
13.   end;
14.   Listbox2.ItemHeight := h;
15. end;

[tailkinker]

Unfortunately, this does not work.  The size returned does not in fact equal the height in pixels of the text when displayed in the listbox.

[wp]

I am on Windows, and the code is working (see also the attached project). But since the listbox is controlled by the widgetset this may not be true for other operating systems. Just run the attached demo and adjust the "extra pixels" (added to the pure "char height") so that the line heights of both listboxes are the same (the left one has Style lbStandard).

[tailkinker]

Well, that works, but it means mucking with the source every time I change environments.  I think I'll look at using a different control.  Thanks to all those that helped.

[wp]

Ah, there's a simpler way: Query the rectangle occupied by an item:

Code: Pascal  [Select][+][-]

1. var
2.   R: TRect;
3. ...
4.   R := AListbox.ItemRect(0);
5.   height := R.Bottom - R.Top;
6.