Author: Boris Benjamin Wittfoth

How to dynamically create a Combobox within a Cell of a StringGrid 

Answer:

You need a descendent of TStringgrid that properly reflects WM_COMMAND to embedded 
controls. The standard grid does not do it since it is not intended to play parent 
to other controls. 

Additionaly simply declare a Set- and GetMethod to access the items of die combobox 

1   unit BWControlStringGrid;
2   
3   interface
4   
5   uses
6     Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
7     Grids, stdctrls;
8   
9   type
10    TBWControlStringGrid = class(TStringGrid)
11    private
12      fComboBox: TCombobox;
13      procedure WMCommand(var msg: TWMCommand); message WM_COMMAND;
14      procedure DblClick; override;
15      procedure Click; override;
16      procedure RelocateComboBox;
17      procedure HideCombobox;
18    protected
19      procedure KeyPress(var Key: Char); override;
20    public
21      constructor Create(AOWner: TComponent); override;
22      destructor Destroy; override;
23    published
24    end;
25  
26  procedure register;
27  
28  implementation
29  
30  procedure register;
31  begin
32    RegisterComponents('hEaDRoOm', [TBWControlStringGrid]);
33  end;
34  
35  procedure TBWControlStringGrid.WMCommand(var msg: TWMCommand);
36  begin
37    if EditorMode and (msg.Ctl = fComboBox.Handle) then
38      inherited
39    else if msg.Ctl <> 0 then
40      msg.result :=
41        SendMessage(msg.ctl, CN_COMMAND,
42        TMessage(msg).wparam,
43        TMessage(msg).lparam);
44  end;
45  
46  procedure TBWControlStringGrid.KeyPress(var Key: Char);
47  begin
48    if Key = #13 then
49      RelocateComboBox
50    else
51      HideCombobox;
52  
53  end;
54  
55  procedure TBWControlStringGrid.DblClick;
56  begin
57    inherited;
58    RelocateComboBox;
59  end;
60  
61  procedure TBWControlStringGrid.Click;
62  begin
63    inherited;
64    HideCombobox;
65  end;
66  
67  procedure TBWControlStringGrid.RelocateComboBox;
68  begin
69    fcombobox.boundsrect := CellRect(Selection.Left, Selection.Top);
70    fcomboBox.Visible := TRUE;
71    fcombobox.setfocus;
72  end;
73  
74  procedure TBWControlStringGrid.HideCombobox;
75  begin
76    fcomboBox.Visible := false;
77  end;
78  
79  constructor TBWControlStringGrid.Create(AOWner: TComponent);
80  begin
81    inherited Create(Aowner);
82    fComboBox := TComboBox.Create(self);
83    fComboBox.Parent := self;
84    fComboBox.Visible := FALSE;
85    Options := Options - [goRangeSelect];
86  end;
87  
88  destructor TBWControlStringGrid.Destroy;
89  begin
90    fComboBox.Destroy;
91    inherited destroy;
92  end;
93  
94  end.


This is great, but is just the skeleton, of course.. 

There needs to be some mechansim for getting the combo's text/selection into the 
cell, also for relaying the cells contents into the combo in the first place. 

This can be done in the Hide and Relocate methods. 

The whole thing can get unwieldy if you add a lot of get/set methods for updating 
the combos dropdownlist, etc, so making the Combo a Public property, rather than 
just a private field might help with that - the onus is then on the programmer to 
deal with the combo directly - it is unlikely, for instance, that the dropdownlist 
would be the same for each column. 

Or two new events could be triggered - OnHide and OnRelocate 
eg: 
95  
96  TComboVisibleChangeEvent = procedure(Sender: TObject; Row, Col: Longint; Combo:
97    TComboBox; AllowVisibleChange: boolean) of object
98  
99  fOnHide: TComboVisibleChangeEvent;
100 fOnRelocate: TComboVisibleChangeEvent;


etc. 

This way the Combo would be make public when needed. When the Relocate fires, the 
dropdownlist could be repopulated, etc 

Just ideas for whoever wants them!