Add Getting fancy with TTreeView


Getting fancy with TTreeView
Overcoming certain problems when custom drawing tree nodes
By: Jody Dawkins

Problem
TTreeView has four events through which to facilitate custom drawing:
- OnCustomDraw
- OnCustomDrawItem
- OnAdvancedCustomDraw
- OnAdvancedCustomDrawItem

The implementation of these events work fine provided you are using them to produce relatively
simple changes in appearance. As long as you are only using one font per node everything
should be fine.

So what are you to do when you want to use multiple fonts in a single node?

Solution
You a number of solutions:
- Use a third-party components
- Write custom TTreeView to solve this problem
- Use the method I'll show here

This method is really a work-around. If you need a solid, high performance solution then you
should seek out a commercially available third-party component. That being said here is my
method:

I needed to produce a "multi-line" tree view. This is to say each node would have more than
one line of text. As you know there is no OnMeasureItem as there is on TListBox and no way
to set the item height for each node. To overcome this I added a TImageList with the Height
property set to 48 and assigned it to the Images property of the TTreeView.

Now I just needed to paint each line in the OnCustomDrawItem event. I intended to make the
first line bold and the second line normal text colored with clAppWorkspace. After discovering
the problems inherit to this situation I decided to draw my text to a bitmap then draw the bitmap
on the TTreeView.

Here's the code:

  1. procedure TForm1.tvDesignViewCustomDrawItem(Sender: TCustomTreeView;
  2.   Node: TTreeNode; State: TCustomDrawState; var DefaultDraw: Boolean);
  3.  
  4.   procedure ChangeFont(Canvas : TCanvas; const NewColor : TColor; const
  5. NewStyle : TFontStyles);
  6.   begin
  7.     Canvas.Font.Style := NewStyle;
  8.     if not (cdsSelected in State) then
  9.       Canvas.Font.Color := NewColor
  10.     else
  11.       Canvas.Font.Color := clHighlightText;
  12.   end;
  13.  
  14. var
  15.   txtrect, fullrect : TRect;
  16.   th : Integer;
  17.   s : string;
  18.   bmp : TBitmap;
  19.   TextLeft : Integer;
  20. begin
  21.   DefaultDraw := False;
  22.   txtrect := Node.DisplayRect(True);
  23.   fullrect := Node.DisplayRect(False);
  24.   txtrect.Right := fullrect.Right; // I want access to the rest of the
  25. space to the right
  26.   bmp := TBitmap.Create;
  27.   try
  28.     bmp.Height := txtrect.Bottom - txtrect.Top;
  29.     bmp.Width := txtrect.Right - txtrect.Left;
  30.     with bmp.Canvas do begin
  31.       Brush.Assign(Sender.Canvas.Brush);
  32.       Pen.Assign(Sender.Canvas.Pen);
  33.       Font.Assign(Sender.Canvas.Font);
  34.       FillRect(ClipRect);
  35.       TextLeft := 2;
  36.       ChangeFont(bmp.Canvas, clWindowText, [fsBold]);
  37.       th := TextHeight('Wg');
  38.       TextOut(TextLeft, 2, Node.Text);
  39.       ChangeFont(bmp.Canvas, clAppWorkSpace, []);
  40.       TextOut(TextLeft, 2 + (th * 1), ‘Here is line 1);
  41.       ChangeFont(bmp.Canvas, clWindowText, []);
  42.       TextOut(TextLeft, 2 + (th * 2), ‘Here is line 2);
  43.     end;
  44.     Sender.Canvas.Draw(txtrect.Left, txtrect.Top, bmp);
  45.   finally
  46.     FreeAndNil(bmp);
  47.   end;
  48. end;


Don’t forget: remember to add the TImageList as described above to create the space needed
for multiple lines.

This example could be further optimized by reusing the same TBitmap instead of creating and
destroying one each time the event is called.

Conclusion
Using this method you can fully customize the look of each node till your heart’s content. I found
it useful. I hope you will too.

- Jody
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