Editing check boxes in a DBGrid

I wrote¹ a few weeks ago about how to make certain fields editable in a data grid. As I wrote towards the end of the blog, The flags are shown as checkboxes drawn on the grid, but when they are edited, their real nature is disclosed - they have one of the values 0 or 1. The user has to enter the appropriate value in order to change the state of the checkbox.

This has nagged me somewhat; it would be better that the user simply press the space bar in order to toggle a flag's value. When I sat down to try and solve this problem a few weeks ago by using the grid's OnKeyPress method, I asked myself how do I know which column is being edited? Today I discovered the answer to that question: the function dbgrid1.selectedfield.FieldName tells me the column's name. Once I had this, some fiddling around gave me the following code (this is after a few iterations):

procedure TDoStatus.DBGrid1KeyPress(Sender: TObject; var Key: Char);
var
 s: string;

 Procedure SetFieldValue (f: TSmallintField);
 var
  n: integer;

 begin
  qDoStatus.Edit;
  n:= f.asinteger;
  if n = 0
   then f.asinteger:= 1
   else f.asinteger:= 0;
  qDoStatus.Post;
 end;

begin
 if key = ' ' then
  begin
   s:= dbgrid1.selectedfield.FieldName;
   if s = 'FUTURE' then SetFieldValue (qDoStatusFuture)
   else if s = 'MEETING' then SetFieldValue (qDoStatusMeeting)
   else if s = 'COPYCONTACT' then SetFieldValue (qDoStatusCopyContact)
   else if s = 'CLOSED' then SetFieldValue (qDoStatusClosed)
   else exit;

   // this stupid code gets the grid to redraw itself
  if qDoStatus.Eof then
   begin
    qDoStatus.Prior;
    qDoStatus.Next;
   end
  else
   begin
    qDoStatus.Next;
    qDoStatus.Prior;
   end;
  end 
end;

This does indeed work, although it's not perfect. First of all, the user can still type 0, 1 or anything else for that matter, and my code doesn't prevent that despite my attempts at doing so. Maybe I should add the end 'else key = #0'. If the user does type 0 or 1, then nothing happens, so at least that's good. Secondly, I don't like the code at the end with the prior/next calls; this seems extravagant, but a call to 'refresh' may do the same fiddling around. Finally, it would be nice if I could make this more abstract by passing a global function the name of the query, although it's not clear at the moment how I would use selectedfield.fieldname. 

Today I was concentrating on writing code that works correctly; I'm sure that tomorrow it will be clear how to turn this localised code (similar code appears in another unit) into something more abstract and global.

Internal links
[1] 1916

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