Call OnDrawCell Directly?
lazarus / 13-General

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Madmensking · 2014-08-26 12:25

Afternoon all,

I'm trying to work out if it is possible to directly call the
onDrawCell procedure to force a String Grid to redraw itself so that
cells in a column can be coloured according to if they match values in
a string list, the code is below and hopefully will make more sense!

Code: [Select]procedure TForm1.StringGrid1DrawCell(Sender: TObject;
aCol, aRow: Integer; aRect: TRect; aState: TGridDrawState);
var
  StringComp: LongInt;
  rc: Integer;
begin
  rc:= ReturnList.Count;
  I:= 1;

     if rc < 1 then
     While i < StringGrid1.RowCount do
     begin
          if i > rc then exit;
         
StringComp:=AnsiCompareStr(ReturnList.Strings[i],StringGrid1.Cells[3,
i]);
          if StringComp = 0 then
             begin
               StringGrid1.Canvas.Brush.Color:=clGreen;
               StringGrid1.Canvas.FillRect(aRect);

               StringGrid1.Canvas.TextRect(aRect, aRect.Left,
aRect.Top, StringGrid1.Cells[3, i]);
               i:= i + 1;

               if gdFocused in aState then
                  StringGrid1.Canvas.DrawFocusRect(aRect);
             end
             else
             begin
               StringGrid1.Canvas.Brush.Color:=clRed;
               StringGrid1.Canvas.FillRect(aRect);

               StringGrid1.Canvas.TextRect(aRect, aRect.Left,
aRect.Top, StringGrid1.Cells[3, i]);
               i:= i + 1;

               if gdFocused in aState then
                  StringGrid1.Canvas.DrawFocusRect(aRect);
             end;
     end;
end;                                       

NOTE
The variable i is declared as a public variable and is used a generic
counter for loops.

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Mike.Cornflake · 2014-08-26 12:36

Don't know about OnDrawCell, but with TDBGrid, I use OnPrepareCanvas
for similar...
http://lazarus-
ccr.sourceforge.net/docs/lcl/grids/tcustomgrid.onpreparecanvas.html

Here's my code for TDBGrid.  I note the parameters for PrepareCanvas
are different for TStringGrid (for TStringGrid you get Row and Col
passed as parameters), but you should get the idea...  Basically, I'm
only setting Canvas.Brush.Colour and Canvas.Font.Colour, the grid does
the actual drawing itself.

Code: [Select]Procedure TFrameGrid.grdSQLPrepareCanvas(Sender:
TObject; DataCol: Integer;
  Column: TColumn; AState: TGridDrawState);
Var
  oField: TField;
  oColor: TColor;
  sColor: String;
Begin
  If Not (gdSelected In AState) Then
  Begin
    oField := FDataset.FindField('Colour_ID');
    If Not Assigned(oField) Then
      oField := FDataset.FindField('Color_ID');

    If Assigned(oField) Then
    Begin
      sColor := Lowercase(oField.Text);

      Case sColor Of
        'red': oColor := TColor($008080FF);
        'green': oColor := TColor($0080FF80);
        'blue': oColor := TColor($00FF9F40);
        'orange': oColor := TColor($0084ACFF);
        'yellow': oColor := TColor($0080FFFF);
        Else
          sColor := 'ignore';
      End;

      If sColor <> 'ignore' Then
      Begin
        If gdRowHighlight In AState Then
          oColor := GetHighLightColor(oColor, 32);

        grdSQL.Canvas.Brush.Color := oColor;
      End;

      grdSQL.Canvas.Font.Color := clBlack;
    End;
  End;
End;

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Madmensking · 2014-08-26 12:48

Cheers Mike,

I will give that a go, I notice it doesn't use any TRect though so
does the code you've given colour the entire row rather than an
individual cell?

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Blaazen · 2014-08-26 12:51

I guess you cannot call StringGrid1DrawCell directly, or, better said,
you can but is no guarantee that anything will be painted. Some
wigdetsets, like Qt and Carbon, does not allow to paint out of Paint
method. Maybe it will work on Windows and GTK2.

A more straightforward method is to assign the OnDrawCell event to the
grid and call StringGrid1.Invalidate. Job will be done in a natural
way.

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Madmensking · 2014-08-26 12:54

Blaazen,

I tried using .invalidate but nothing happened?

Even when I put a break in at the beginning on the drawcell after the
invalidate had been run, ondrawcell was not called..

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Mike.Cornflake · 2014-08-26 12:58

Quote from: Madmensking on August 26, 2014, 02:48:55 pmCheers Mike,

I will give that a go, I notice it doesn't use any TRect though so
does the code you've given colour the entire row rather than an
individual cell?
It's the different parameters thing I was talking about.  For
TStringGrid, your parameters will include Row and Column, so you'll be
doing for an individual cell.
My code is actually suboptimal as I'm doing the same Field Lookup once
for every column per record in the dataset.  And I've only just
noticed, so thanks for your question 

As for the lack of rect, there's no drawing going on inside
PrepareCanvas.  The grid does the drawing.  It just uses the brush,
pen, font etc that you set up for it in OnPrepareCanvas.