Author: Tomas Rutkauskas

I have a TStringGrid component and I want change the color of the text in one row.

Answer:

Any kind of custom drawing in a TStringgrid requires a OnDrawCell handler (or 
overriding the DrawCell method in a derived grid class). Often this is not 
enough,however. If you base your special drawing on the active cell or its row or 
column you also need to make sure cells you previously drew in your custom manner 
are redrawn normal when the active cell moves, that the grid shows the special 
drawing only when it has focus and so on. This can get a bit complex, as shown by 
the sample below.

Note that is is simpler when you only customize the active cell, since this cell 
will be redrawn automatically when it is activated or deactivated.

1   unit Unit1;
2   
3   interface
4   
5   uses
6     Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
7     ComCtrls, StdCtrls, Grids;
8   
9   const
10    UM_INVALIDATEROW = WM_USER + 321;
11  type
12    TForm1 = class(TForm)
13      StatusBar: TStatusBar;
14      Button1: TButton;
15      OpenDialog1: TOpenDialog;
16      Label1: TLabel;
17      StringGrid1: TStringGrid;
18      Edit1: TEdit;
19      procedure StringGrid1DrawCell(Sender: TObject; ACol, ARow: Integer; Rect: TRect;
20        State: TGridDrawState);
21      procedure StringGrid1Enter(Sender: TObject);
22      procedure StringGrid1SelectCell(Sender: TObject; ACol, ARow: Integer; var
23        CanSelect: Boolean);
24      procedure StringGrid1Exit(Sender: TObject);
25    private
26      { Private declarations }
27      FGridActive: Boolean;
28      procedure UMInvalidateRow(var msg: TMessage); message UM_INVALIDATEROW;
29    public
30      { Public declarations }
31    end;
32  
33  var
34    Form1: TForm1;
35    dummy: Integer;
36  
37  implementation
38  
39  {$R *.DFM}
40  
41  type
42    TGridCracker = class(TStringgrid); { gives access to protected methods }
43  
44  procedure TForm1.StringGrid1DrawCell(Sender: TObject; ACol, ARow: Integer;
45    Rect: TRect; State: TGridDrawState);
46  var
47    grid: TStringgrid;
48  begin
49    {Task: color the current row}
50    grid := Sender as TStringgrid;
51    if FGridActive and (aRow = grid.Row) and (aCol >= grid.FixedCols) then
52    begin
53      grid.Canvas.brush.Color := clBlue;
54      grid.canvas.font.color := clWhite;
55      grid.canvas.FillRect(Rect);
56      InflateRect(rect, -2, -2);
57      grid.Canvas.TextRect(Rect, rect.left, rect.top, grid.cells[aCol, aRow]);
58    end
59    else if (gdSelected in State) and not grid.Focused then
60    begin
61      grid.Canvas.brush.Color := grid.color;
62      grid.canvas.font.color := grid.font.color;
63      grid.canvas.FillRect(Rect);
64      InflateRect(rect, -2, -2);
65      grid.Canvas.TextRect(Rect, rect.left, rect.top, grid.cells[aCol, aRow]);
66    end;
67  end;
68  
69  procedure TForm1.StringGrid1Enter(Sender: TObject);
70  begin
71    if Sender is TStringgrid then
72      with TGridCracker(sender) do
73        PostMessage(self.handle, UM_INVALIDATEROW, Row, Integer(sender));
74    FGridActive := true;
75    { Cannot rely on grid.focused here, it is not yet true when the message send
76    above is processed for some reason. }
77  end;
78  
79  procedure TForm1.StringGrid1SelectCell(Sender: TObject; ACol, ARow: Integer;
80    var CanSelect: Boolean);
81  var
82    grid: TStringgrid;
83  begin
84    grid := Sender as TStringgrid;
85    if grid.Row <> aRow then
86      PostMessage(handle, UM_INVALIDATEROW, grid.Row, Integer(grid));
87    PostMessage(handle, UM_INVALIDATEROW, aRow, Integer(grid));
88  end;
89  
90  procedure TForm1.UMInvalidateRow(var msg: TMessage);
91  begin
92    TGridCracker(msg.lparam).InvalidateRow(msg.wparam);
93  end;
94  
95  procedure TForm1.StringGrid1Exit(Sender: TObject);
96  begin
97    if Sender is TStringgrid then
98      with TGridCracker(sender) do
99        PostMessage(self.handle, UM_INVALIDATEROW, Row, Integer(sender));
100   FGridActive := false;
101 end;
102 
103 end.