DBGrid: how to prevent a row from being selected?

Question

I have a grid of entries the user will click on to multi-select for a process. Some of the entries will be invalid based upon values of the first selected row.

I know about DBGrid.SelectedRows.CurrentRowSelected, but I cannot find a suitable place for checking my conditions to set it to True or False.

Something like this:

var
  bm: TBookmark;
  CachedIdentity: String;
  CanSelect: Boolean;
begin
  with dgbSkypeConversations do
  begin
    if SelectedRows.Count > 0 then
    begin
      DataSource.DataSet.DisableControls;
      bm := DataSource.DataSet.GetBookmark;
      CachedIdentity := DataSource.DataSet.FieldByName('identity').AsString;
      DataSource.DataSet.GotoBookmark(SelectedRows[0]);
      CanSelect := DataSource.DataSet.FieldByName('identity').AsString <> CachedIdentity;
      DataSource.DataSet.GotoBookmark(bm);
      DataSource.DataSet.FreeBookmark(bm);
      SelectedRows.CurrentRowSelected := CanSelect; 
      DataSource.DataSet.EnableControls;
    end;
  end
end;

I have tried the OnMouseDown events in Application.OnMessage and of the DBGrid and the Form, but they do not work, and there is no TBookmarkList.BeforeInsertItem event. What can I do or must I change?

Your q's title doesn't seem to match what you describe in the text of the q. Are you trying to prevent the user selecting some rows in the grid? If so, why no just prevent them being displayed in the first place, e.g. by using a filter on the grid's dataset? — Alex James
First part: yes. Second because the user needs to see the data and then decide what to select, not before... I´ve done all the filter thing you can imagine, but i cant change the user requirement — José Eduardo
Once the user has made the first selection (which is the point you want to disable rows), you can filter to remove the non-eligible rows, which is much cleaner from a UI standpoint. While you might hack in a way to prevent the user from selecting certain rows, at that point you can't draw them differently to indicate they're disabled (not selectable). — Ken White

moskito-x moskito-x · Accepted Answer · 2016-04-19T20:48:34

I would not make it so complicated.
If the comparison always takes place on the first selection.
The code I use here has hardcoded Value.
No jump around to bookmarks.

// first selection----------------------------- 
if DBGrid1.SelectedRows.Count = 1 then begin
   CachedIdentity := 'Sonnenbrille'; // Sunglasses
 //CachedIdentity := DataSource.DataSet.FieldByName('identity').AsString;
   Exit;
end;

Do the comparison

if DBGrid1.SelectedRows.CurrentRowSelected then begin
 //if CachedIdentity <> DataSource.DataSet.FieldByName('identity').AsString
   if Pos(LookingFor,DBGrid1.DataSource.DataSet.FieldByName('haupttxt').AsString)=0
   then  DBGrid1.SelectedRows.CurrentRowSelected := False;
   ShowMessage(IntToStr(DBGrid1.SelectedRows.Count));
end;

We can see two are selected so
ShowMessage(IntToStr(DBGrid1.SelectedRows.Count));

shows 2

Now we want to select the line

SPORTLICH, ELEGANTE GUCCI SONNENBRILLE

We know a simple Pos() Sonnenbrille to find SONNENBRILLE Pos() will be = 0, so a selection-will not take place.

ShowMessage(IntToStr(DBGrid1.SelectedRows.Count));

shows 2 too

CODE:

var
CachedIdentity : string;

procedure TForm2.canSelectedV1;
begin
    // first selection----------------------------- 
if DBGrid1.SelectedRows.Count = 1 then begin
   CachedIdentity := 'Sonnenbrille'; // Sunglasses
 //CachedIdentity := DataSource.DataSet.FieldByName('identity').AsString;
   Exit;
end;
if DBGrid1.SelectedRows.CurrentRowSelected then
 begin
 //if CachedIdentity <> DataSource.DataSet.FieldByName('identity').AsString
   if Pos(LookingFor,DBGrid1.DataSource.DataSet.FieldByName('haupttxt').AsString)=0
   then  DBGrid1.SelectedRows.CurrentRowSelected := False;
   ShowMessage(IntToStr(DBGrid1.SelectedRows.Count));
 end;
end;

procedure TForm2.DBGrid1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
canSelectedV1;
end;

procedure TForm2.DBGrid1KeyUp(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
canSelectedV1;
end;

end.

DBGrid: how to prevent a row from being selected?

2 Answers