Author: Jonas Bilinkevicius

How to draw checkboxes in a TDBGrid

Answer:

Two procedures follow. The first is called from the OnDrawColumnCell event of any 
grid that has visible boolean fields, as so:

procedure TForm1.DBGrid1DrawColumnCell(Sender: TObject; const Rect: TRect;
  DataCol: Integer; Column: TColumn; State: TGridDrawState);
begin
  DrawCheckBoxes(Sender, Rect, DataCol, Column, State);
end;

Here's the procedure. Place this in your toolkit or utility unit.
1   
2   procedure DrawCheckBoxes(Sender: TObject; const Rect: TRect;
3     DataCol: Integer; Column: TColumn; State: TGridDrawState);
4   var
5     MyRect: TRect;
6     fld: TField;
7   begin
8     with (Sender as TDBGrid) do
9     begin
10      fld := Column.Field;
11      if fld is TBooleanField then
12      begin
13        MyRect.Top := ((Rect.Bottom - Rect.Top - 11) div 2) + Rect.Top;
14        MyRect.Left := ((Rect.Right - Rect.Left - 11) div 2) + Rect.Left;
15        MyRect.Bottom := MyRect.Top + 10;
16        MyRect.Right := MyRect.Left + 10;
17        if gdSelected in State then
18          Canvas.Pen.Color := clWhite
19        else
20          Canvas.Pen.Color := clBlack;
21        Canvas.Polyline([
22          Point(MyRect.Left, MyRect.Top), Point(MyRect.Right, MyRect.Top),
23            Point(MyRect.Right, MyRect.Bottom), Point(MyRect.Left, MyRect.Bottom),
24            Point(MyRect.Left, MyRect.Top)]);
25        if fld.AsBoolean then
26        begin
27          Canvas.MoveTo(MyRect.Left + 2, MyRect.Top + 4);
28          Canvas.LineTo(MyRect.Left + 2, MyRect.Top + 7);
29          Canvas.MoveTo(MyRect.Left + 3, MyRect.Top + 5);
30          Canvas.LineTo(MyRect.Left + 3, MyRect.Top + 8);
31          Canvas.MoveTo(MyRect.Left + 4, MyRect.Top + 6);
32          Canvas.LineTo(MyRect.Left + 4, MyRect.Top + 9);
33          Canvas.MoveTo(MyRect.Left + 5, MyRect.Top + 5);
34          Canvas.LineTo(MyRect.Left + 5, MyRect.Top + 8);
35          Canvas.MoveTo(MyRect.Left + 6, MyRect.Top + 4);
36          Canvas.LineTo(MyRect.Left + 6, MyRect.Top + 7);
37          Canvas.MoveTo(MyRect.Left + 7, MyRect.Top + 3);
38          Canvas.LineTo(MyRect.Left + 7, MyRect.Top + 6);
39          Canvas.MoveTo(MyRect.Left + 8, MyRect.Top + 2);
40          Canvas.LineTo(MyRect.Left + 8, MyRect.Top + 5);
41        end;
42      end;
43    end;
44  end;


There's a little setup involved. Select each visible boolean field in the fields 
editor and set the DisplayValues to ' ;'. That's space + semicolon. I like the 
DisplayWidth set to 2.

The next procedure is optional/ extra. It's a keystroke handler that will change 
the value of the field if the user presses space, T, F, Y, or N.Place it in your 
utility unit also and call it from your OnKeyPress event in the grid as so:
45  
46  procedure TForm1.DBGrid1KeyPress(Sender: TObject; var Key: Char);
47  begin
48    CheckBoxKeyPress(Sender, Key);
49  end;
50  
51  and here's the procedure:
52  
53  procedure CheckBoxKeyPress(const Sender: TObject; var Key: Char);
54  var
55    fld: TField;
56    tbl: TDataset;
57    i: integer;
58  begin
59    if UpCase(Key) in ['] then
60    begin
61      with (Sender as TDBGrid) do
62      begin
63        i := SelectedIndex;
64        fld := SelectedField;
65        tbl := fld.DataSet;
66        if fld is TBooleanField then
67        begin
68          if not (tbl.State in [dsEdit, dsInsert]) then
69            tbl.Edit;
70          if Key = ' ' then
71            fld.AsBoolean := not fld.AsBoolean
72          else if (UpCase(Key) = 'T') or (UpCase(Key) = 'Y') then
73            fld.AsBoolean := True
74          else
75            fld.AsBoolean := False;
76          tbl.Post;
77          Key := #0;
78          Inc(i);
79          if i = FieldCount then
80          begin
81            i := 0;
82            tbl.Next;
83            if tbl.EOF then
84              tbl.Append;
85          end;
86          SelectedIndex := i;
87        end;
88      end;
89    end;
90  end;