Author: Eugene Mayevski

It is possible to specify initial folder in Open/Save dialogs. However sometimes it 
is necessary to change current folder, for example, in responce to change of 
filter. 

Answer:

Windows doesn't offer a way to change current dialog. However there is a very handy 
approach to this problem - imitate user actions. Below is the sample code of how 
the folder is changed when filter is changed. 

procedure SaveDialogTypeChange is a handler for OnTypeChange event. 
Depending on the type different folders are selected. This piece of code saves the 
value of file name edit box, puts a new folder name there, then imitates click of 
OK button and then restores contents of the edit box. 
Add Dlgs to "uses" clause of your unit.
1   
2   procedure TMainForm.SaveDialogTypeChange(Sender: TObject);
3   var
4     S, S1: string;
5     EditHandle: THandle;
6     startp,
7       endp: DWORD;
8   begin
9     s := '';
10    if SaveDialog.FilterIndex = 2 then
11    begin
12      s := 'c:\program files';
13    end
14    else if SaveDialog.FilterIndex = 3 then
15    begin
16      s := 'd:\program files';
17    end;
18    if s <> '' then
19    begin
20      EditHandle := GetDlgItem(GetParent(SaveDialog.Handle), edt1);
21      if EditHandle <> 0 then
22      begin
23        SetLength(S1, GetWindowTextLength(EditHandle) + 1);
24        GetWindowText(EditHandle, PChar(S1), Length(S1));
25        SetLength(S1, StrLen(PChar(S1)));
26        SendMessage(EditHandle, EM_GETSEL, Integer(@StartP), Integer(@EndP));
27        SetWindowText(EditHandle, PChar(S));
28        SendMessage(GetParent(SaveDialog.Handle), WM_COMMAND, 1,
29          GetDlgItem(GetParent(SaveDialog.Handle), IDOK));
30        if Length(S1) > 0 then
31          if S1[Length(S1)] = #10 then
32            Delete(S1, Length(S1), 1);
33        SetWindowText(EditHandle, PChar(S1));
34        SendMessage(EditHandle, EM_SETSEL, StartP, EndP);
35      end;
36    end;
37  end;