OnDropDown (C++)

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; if the application opens or closes forms, the combo box stays current.

Code

#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 ((reinterpret_cast<TForm1 *>(Screen->CustomForms[i]))->Visible)
	  ComboBox1->Items->Add(Screen->CustomForms[i]->Caption);  // Add form names.
  }
  ComboBox1->Items->EndUpdate(); //Re-enable painting.
}

__fastcall TForm1::TForm1(TComponent* Owner)
  : TForm(Owner)
{
  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();
}

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 )