Luca,
Intercept classes are a very useful technique for overcoming this
problem. I recently wanted to have a specialised TComboBox as a
TStringGrid Editor and defined an intercept class for this as:
TComboBox = class(stdctrls.TComboBox)
private
FGrid: TCustomGrid;
FCol,FRow: Integer;
protected
procedure WndProc(var TheMessage : TLMessage); override;
procedure CloseUp; override;
procedure KeyDown(var Key : Word; Shift : TShiftState); override;
procedure Loaded; override;
procedure msg_GetValue(var Msg: TGridMessage); message GM_GETVALUE;
procedure msg_SetGrid(var Msg: TGridMessage); message GM_SETGRID;
procedure msg_SetValue(var Msg: TGridMessage); message GM_SETVALUE;
procedure msg_SetPos(var Msg: TGridMessage); message GM_SETPOS;
procedure msg_GetGrid(var Msg: TGridMessage); message GM_GETGRID;
public
procedure EditingDone; override;
property BorderStyle;
property OnEditingDone;
end;
The result was a specialist editor for the stringgrid (and which handles
TGridMessage) but which could be placed on the form and edited as a
TComboBox. The TStringFrid "OnSelectEditor " event is then used to
return the combobox as an editor.
Intercept classes can be used to customise just about any component.
Just ensure that your intercept class is defined after the parent class.
Tony Whyman
MWA
On 02/11/15 10:12, Luca Olivetti wrote:
Hello,
I constantly stumble with the behaviour of the TDBGrid.
I understand that it's a complex component, but every time I find an
issue an Luiz fixes it, two more pop up (or an older one resurfaces).
The latest episode of the saga is the futility of using a custom
editor (with OnSelectEditor), since the grids then sets the value of
the field using this snippet of code
if (FEditor<>nil) and FEditor.Visible then begin
Msg.LclMsg.msg:=GM_GETVALUE;
Msg.grid:=Self;
Msg.Col:=FCol;
Msg.Row:=FRow;
Msg.Value:=GetCells(FCol, FRow);
FEditor.Dispatch(Msg);
SetEditText(Msg.Col, Msg.Row, Msg.Value);
end;
and this only works with the editors defined in Grids.pas, the only
ones managing the GM_GETVALUE message.
For other kinds of editors the result depends on how you move in the
grid: it could either maintain the value the editor set or reset it to
an empty string.
I think I will file a bug once I can create a simple project, but in
the meantime if somebody has an idea on how to solve it, it would be
appreciated.
Oh, and a custom editor has no way of adapting if the dbgrid is
scrolled, a column is resized, etc. Again, this only work for the
editors defined in Grids.pas.
Bye
--
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