Showing hint with content of a cell in a DBGrid (SOLVED)

[derles]

Hello all.
I have the need of showing a hint with the content of a cell of a DBGrid when the mouse moves over the cell (not current cell).
I was using Lazarus 1.0.10 and FPC 2.6.2, and solved the issue with this code, simulating the hint with a memo control:

Code: Pascal  [Select][+][-]

1. type
2.   TMyGrid = Class(TCustomDBGrid);
3.  
4. procedure TForm1.dbgrid1MouseMove(Sender: TObject;Shift: TShiftState; X, Y: Integer);
5. var
6.   row, col: integer;
7.   rec: integer;
8. begin
9.   inherited;
10.  
11.   TDBGrid(Sender).MouseToCell(X, Y, col, row);
12.  
13.   if dgTitles in TDBGrid(Sender).Options then
14.     Dec(row);
15.  
16.   if TMyGrid(TDBGrid(Sender)).DataLink.Active and (row >= 0) and (col = 2) then
17.   begin
18.     rec := TMyGrid(TDBGrid(Sender)).DataLink.ActiveRecord;
19.  
20.     try
21.       TMyGrid(TDBGrid(Sender)).DataLink.ActiveRecord := row;
22.  
23.       Memo1.Text := TDBGrid(Sender).Columns[col].Field.AsString;
24.       Memo1.Visible := True;
25.     finally
26.       TMyGrid(TDBGrid(Sender)).DataLink.ActiveRecord := rec;
27.     end;
28.   end
29.   else
30.   begin
31.     Memo1.Text := '';
32.     Memo1.Visible := False;
33.   end;
34. end;
35.  

Last week I updated Lazarus to 1.6.4, FPC 3.02, and in the same code I have a typecast error at compliling:
Error: Class or Object types "TDBGrid" and "TMyGrid" are not related
in every line with the code TMyGrid(TDBGrid(Sender)).DataLink.Active

If I replace
TMyGrid(TDBGrid(Sender)).DataLink.Active
with
TMyGrid(TCustomDBGrid(Sender)).DataLink.Active
i have no error at compliling, but this error at runtime:
Invalid TypeCast

If not use TMyGrid, using just the typecast
TCustomDBGrid(Sender).DataLink.Active
i have this compliling error:
Error: identifier idents no member "DataLink"


After a few days working on it, I still can't figure out how to solve this.
Any suggestion ?

I use Firebird and ZeosLib.

TKS !

[wp]

Forget this old code, cell hints have been built in some time ago: http://wiki.lazarus.freepascal.org/Grids_Reference_Page#Cell_hints

Besides that, the "hacking" type-cast is wrong. In order to access a protected property of a component you must declare a descendant of this component, not of its ancestor, i.e. you must declare TMyGrid = class(TDBGriid) not class(TDBCustomGrid). If this had been working in Laz 1.0.10 then it was a bug.

Instead of the double cast do a single cast. TMyGrid(Sender).DataLink.ActiveRecord.

You could also work with bookmarks.

[derles]

Now, this was a truly deeply helpful reply. My grid now works as I dreamed.

Thank you very much wp.

 

[patyi]

Hi !

I have error: invalid type cast in this code.
i386 XUbuntu 17.10, Lazarus 1.8.0RC4 from 09.10.2017, FPC 3.03 installed with FpcUpDelux Fixex branch.

Code: Pascal  [Select][+][-]

1. type
2.   TMyGrid = class(TDBGrid);
3.  
4. procedure TForm.DBGrid1MouseMove(Sender: TObject; Shift: TShiftState; X,
5.   Y: Integer);
6. var
7.   row, col : integer;
8.   rec : integer;
9. begin
10.   inherited;
11.  
12.   TDBGrid(Sender).MouseToCell(X, Y, col, row);
13.   if dgTitles in TDBGrid(Sender).Options then
14.     Dec(row);
15.   if dgIndicator in TDBGrid(Sender).Options then
16.     Dec(col);
17.  
18.   if TMyGrid(Sender).DataLink.Active and (row >= 0) and (col >= 0) then begin  // here is error : Invalid type cast
19.     rec := TMyGrid(Sender).DataLink.ActiveRecord;
20.     try
21.       TMyGrid(Sender).DataLink.ActiveRecord := row;
22.     finally
23.       TMyGrid(Sender).DataLink.ActiveRecord:= rec;
24.     end;
25.   end;
26. end;  

I no idea wat is wrong !  Thanks.

[wp]

It is working for me. But I guess that the event is not generated by a DBGrid. Instead of a type-cast (TDBGrid(Sender)) use operator "as" (Sender as TDBGrid) - it raises an exception if the sender is not a DBGrid. To further help you with debugging you can also check the class by "is" and show a message with the true class name

Code: Pascal  [Select][+][-]

1. procedure TForm1.DBGrid1MouseMove(Sender: TObject; Shift: TShiftState;
2.   X, Y: Integer);
3. var
4.   row, col : integer;
5.   rec : integer;
6. begin
7.   inherited;
8.  
9.   if not (Sender is TDBGrid) then
10.     ShowMessage('Sender is not a TDBGrid but a ' + sender.ClassName + '. Its name is ' + Sender.Name);
11.  
12.   ...

[patyi]

Event is generated by DBGrid !  Traing to insert suggested message about class name, no message is paper that Sender is not TDBGrid.

[wp]

Then you must try to extract the DBGrid part of your project into a small demo which shows the error. Pack .pas, .lfm, lpi, lpr and database file into a shared zip which can be uploaded here (no compiler-generated files, please). And it would be fine if you could show the issue with a little standard database (dbf, memorydataset, bufdataset, sqlite3, or so), no big server system.

[patyi]

Hi !
Now it is working ! If you are using DEBUG mode, the -CR compiler option must be switched off !
Everything is OK if you use DEFAULT or RELEASE modes, because the -CR is off by default ...

Thank you wp for pointing me to the problem!