How to use onDrawColumnCell to change cell text without using textout on Delphi?

Question

I would like to ask if there is another way to alter the cell text without using TextOut()? Using TextOut() requires coordinates which I do not want to mingle into. Besides, I just want to change the text and retain everything else, like color, font, alignment, etc.

My purpose is to alter the display of text in different scenarios. For example:

I may want to show a date field in different formats in different columns, like one column to show in MM/yyyy and another column to show in MM/dd/yyyy.
I may want to display some rows with integer/float datatype with a text that says "too high" or "too low" if the figure is above or below a certain threshold.
I may want to exchange boolean true/false with some text or numbers as I see fit.
or perhaps, just blank some cell on certain conditions.

I understand if TDBGrid is "editable", this would be a tough challenge to do editing. So I intend to use whatever solution in a non-editable grid. And also, I don't want to shift to TStringGrid as I find TDBGrid to be easy to work with a dataset.

Btw, I'm using Delphi 7.

For just leaving a certain cell blank on a certain condition, is there something that I could just issue an "exit" to skip the showing of the cell value into the cell itself?

Like:

procedure Tform1.dbgrdDrawColumnCell(Sender: TObject;  const Rect: TRect; DataCol: Integer; Column: TColumn;  State: TGridDrawState);
begin
  if (Column.fieldname = 'total') and (column.field.value=0) then 
    exit 
  else
    dbgrdsku.DefaultDrawColumnCell(Rect, DataCol, Column, State);
end;

You can't do it by TDBGrid. You can handle all drawing by your self to do all this staff or switch to some other components (TDBGridEh from EhLib for example) which support customization like this. — Oleksandr Morozevych, Nov 13 '22 at 12:00
You can't do that in a DBGrid without doing the drawing and TextOut. You can do most of what you're asking by either a) using a calculated field in your dataset, which you would then display in the grid instead of the actual column; or b) using the TField.OnGetText event for the specific field in the dataset. The first option is the easiest to use. — Ken White, Nov 13 '22 at 23:10
You can also add calculated fields that are all done client side / in Delphi to the TDataSet descendant (Query, table etc). Then assign whatever you want to them in the OnCalcFields event that is called for each record as needed. — Brian, Nov 15 '22 at 03:27
Thank you all for the feedbacks. It seems OnGetText is the only best choice to work on. — jwan, Nov 15 '22 at 07:18

score 1 · Accepted Answer · answered Nov 14 '22 at 15:57

If you are working with a TDBGrid and data sources, before opting for changes in the Grid directly, check if it is useful to do it in the data source (on TFields).

Using the Datasource does not spend so many resources painting. Upon reaching that point (painted) the data may already be changed.

You can create the TFields on TDataset descendant (TQuery, TADOQuery, TFDQuery,...) and use the OnGetText event to change the text to paint. Simpler and better.

If you are two fields like this:

With a simple code like this using the OnGetText of two fields:

procedure TForm3.ADOQuery1DatosGrupoGetText(Sender: TField; var Text: string;  DisplayText: Boolean);
begin
  // too hight for number greater than 5
  if (not Sender.IsNull) then
    if (Sender.AsInteger > 5) then
      Text := 'too hight!'
    else
      Text := Sender.AsString;
end;

procedure TForm3.ADOQuery1fechaGetText(Sender: TField; var Text: string;  DisplayText: Boolean);
begin
  // Change the date format
  if (not Sender.IsNull) then
    Text := formatDateTime('MM/yyyy', Sender.AsDateTime)
end;

You got this result:

How to use onDrawColumnCell to change cell text without using textout on Delphi?

1 Answers1