When is TDBGrid.SelectedRows updated in Delphi?

Question

I want to list some values (ID-s in this case) of the selected rows of a TDBGrid in a TEdit control.

I've tried AfterScroll event, to catch the event after(!) a selection, but it doesn't work if I use the mouse.

If I click on a row with mouse, it doesn't appear in the TDBGrid.SelectedRows collection, only after the next click/selection. If I do the selection with keyboard, everything works fine.

Do you have any idea, how to solve this?

Simplified code of my solution:

procedure TForm1.ClientDataSet1AfterScroll(DataSet: TDataSet);
begin
    edtIDs.Text := string.Join(',', GetSelectedIDs().ToArray) ;
end;

function TForm1.GetSelectedIDs() : TList<string>;
var
    i: Integer;
    ds: TDataSet;
    bmOrig: TBookmark;
begin
    FSelectedIDs.Clear();
    ds := DBGrid1.DataSource.DataSet;
    bmOrig := ds.GetBookmark();
    ds.AfterScroll := nil;                          //switch off AfterScroll event
    try
        if DBGrid1.SelectedRows.Count > 0 then begin
            for i := 0 to DBGrid1.SelectedRows.Count - 1 do begin
                ds.GotoBookmark(DBGrid1.SelectedRows.Items[i]);
                FSelectedIDs.Add(ds.FindField('ID').AsString);
            end;
            ds.GotoBookmark(bmOrig);
        end;
    finally
        ds.AfterScroll := ClientDataSet1AfterScroll; //switch on AfterScroll event
        ds.FreeBookmark(bmOrig);
    end;
    Result := FSelectedIDs;
end;

This way of building a list of selected rows seems avoidably inefficient because you visit each of the selected rows any time the dataset scrolls. Btw, you should surround the for loop by calls to ds.DisableControls & ds.EnableControls to avoid unneccessary screen updates. — MartynA

Schneider Infosystems Ltd Schneider Infosystems Ltd · Accepted Answer · 2019-12-02T13:08:02

Replace the OnAfterScroll event of the data source by the OnColEnter event of the TDBGrid.

Form the help of TDBGrid.OnColEnter:

Occurs when focus moves to a new cell in the grid.

Write an OnColEnter event handler to take specific action when a new cell has just been selected.

Focus moves to a cell when

The user navigates to the cell using the keyboard. For example, when the user uses the Tab key, or the Home key.
The user clicks the mouse button down in the cell.
The SelectedField or SelectedIndex property is set.

Read the SelectedField or SelectedIndex property to determine which cell was just entered.

When is TDBGrid.SelectedRows updated in Delphi?

1 Answers