OnDropDown (Delphi)

Description

This example fills the list of a combo box with the set of open forms when you drop down the list. The list is regenerated every time the list is dropped down, so if the application opens or closes forms, the combo box stays current.

Code

procedure TForm1.ComboBox1DropDown(Sender: TObject);
var
  I: Integer;
begin
  with ComboBox1 do
  begin
    Items.BeginUpdate; { Prevent repaints until done. }
    Items.Clear; { Empty the list of any old values. }
    for I := 0 to Screen.CustomFormCount - 1 do
    begin
      if (Screen.CustomForms[I].Visible) then
        Items.Add(Screen.CustomForms[I].Caption); { Add form name. }
    end;
    Items.EndUpdate; {Reenable painting. }
  end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  ComboBox1.Sorted := True; { Make sure the form names are sorted. }
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Form2.Show;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  Form3.Show;
end;

Uses

• Vcl.StdCtrls.TCustomCombo.OnDropDown ( fr | de | ja )
• Vcl.StdCtrls.TCustomComboBox.Sorted ( fr | de | ja )
• System.Classes.TStrings.Clear ( fr | de | ja )
• System.Classes.TStrings.BeginUpdate ( fr | de | ja )
• System.Classes.TStrings.EndUpdate ( fr | de | ja )