TCustomCombo.OnDropDown Event

Occurs when the user opens the drop-down list.

Pascal

property OnDropDown: TNotifyEvent;

C++

__property TNotifyEvent OnDropDown;

Description

Write an OnDropDown event handler to implement special processing that needs to occur only when the drop-down list is activated.

C++ Examples:

Copy Code

/*
This example fills the list of a combo box with the set of
open forms when the user drops 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.
*/
#include "Unit2.h"
#include "Unit3.h"

void __fastcall TForm1::ComboBox1DropDown(TObject *Sender)
{
  ComboBox1->Items->BeginUpdate(); // prevent repaints until done
  ComboBox1->Items->Clear(); // empty the list of any old values
  for (int i = 0; i < Screen->CustomFormCount; i++)
  {
    if (((TForm1 *)Screen->CustomForms[i])->Visible)
      ComboBox1->Items->Add(Screen->CustomForms[i]->Caption);  // add form names
  }
  ComboBox1->Items->EndUpdate(); //reenable painting
}

void __fastcall TForm1::FormCreate(TObject *Sender)
{
  ComboBox1->Sorted = True; // make sure the form names are sorted
}

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  Form2->Show();
}

void __fastcall TForm1::Button2Click(TObject *Sender)
{
  Form3->Show();
}

Delphi Examples:

Copy Code

{
This example fills the list of a combo box with the set of
open forms when the user drops 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.
}
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;