Now, each Column in a grid is "linked" to a field from a dataset displayed in the grid. What's more, each column has a PickList property. The PickList property lists values that the user can select for the column's linked field value.

Filling the PickList

Here's how to set up the PickList property. First, we add a call to the SetupGridPickList procedure in the Form's OnCreate event handler.

procedure TForm1.FormCreate(Sender: TObject);
begin
  SetupGridPickList('Subject', 'SELECT Name FROM Subjects');
end;

The easiest way to create the SetupGridPickList procedure is to go to the private part of the form declaration, add the declaration there and hit the CTRL + SHIF + C key combination - Delphi's code completion will do the rest:

...
type
  TForm1 = class(TForm)
...
  private
    procedure SetupGridPickList(
        const FieldName : string; 
        const sql : string);
  public
...

Note: the SetupGridPickList procedure takes two parameters. The first parameter, FieldName, is the name of the field we want to act like a lookup field; the second parameter, sql, is the SQL expression we use to populate the PickList with possible values - in general the SQL expression should return a datataset with only one field.

Here's how the SetupGridPickList looks like:

procedure TForm1.SetupGridPickList(const FieldName, sql: string);
var 
  slPickList:TStringList;
  Query : TADOQuery;
  i : integer;
begin
  slPickList:=TStringList.Create;
  Query := TADOQuery.Create(self);
  try
    Query.Connection := ADOConnection1;
    Query.SQL.Text := sql;
    Query.Open;
    //Fill the string list
    while not Query.EOF do
    begin
      slPickList.Add(Query.Fields[0].AsString);
      Query.Next;
    end; //while

    //place the list it the correct column
    for i:=0 to DBGrid1.Columns.Count-1 do 
      if DBGrid1.Columns[i].FieldName = FieldName then
      begin
        DBGrid1.Columns[i].PickList:=slPickList;
        Break;
      end;
  finally
    slPickList.Free;
    Query.Free;
  end; 
end; (*SetupGridPickList*)

That's it. Now, when you click the Subject column (to enter into edit mode), you'll get the next picture:

Note 1: by default, the drop-down list displays 7 values. You can change the length of this list by setting the DropDownRows property.

Note 2: nothing stops you from filling up the PickList from a list of values not coming from a database table. If, for example, you have a field that only accepts week day names ('Monday', ..., 'Sunday') you can build a "hard-coded" PickList.

"Uh, I need to click the PickList 4 times..."

procedure TForm1.DBGrid1CellClick(Column: TColumn);
begin
  //Making the drop-down pick list appear faster
  if Column.PickList.Count > 0 then
  begin
    keybd_event(VK_F2,0,0,0);
    keybd_event(VK_F2,0,KEYEVENTF_KEYUP,0);
    keybd_event(VK_MENU,0,0,0);
    keybd_event(VK_DOWN,0,0,0);
    keybd_event(VK_DOWN,0,KEYEVENTF_KEYUP,0);
    keybd_event(VK_MENU,0,KEYEVENTF_KEYUP,0);
  end;
end;

That's all folks

If you need any help, please post all your problems (and/or suggestions) to the About Delphi Programming Forum.