TObject::Free Method

Destroys an object and frees its associated memory, if necessary.

Pascal

procedure Free;

C++

__fastcall Free();

Description

Use System::TObject::Free to destroy an object. System::TObject::Free automatically calls the destructor if the object reference is not nil. Any object instantiated at runtime that does not have an owner should be destroyed by a call to System::TObject::Free so that it can be properly disposed of and its memory released. Unlike System::TObject::Destroy, System::TObject::Free is successful even if the object is nil; so if the object was never initialized, System::TObject::Free won't result in an error.

When you call System::TObject::Free for a component, it calls System::TObject::Free for all components that it owns—that is, all components in its component list. Since a form owns all the controls and other components that are created on it in design mode, those components are automatically freed when the form is freed. By default, all forms are owned by the Application object; when the application terminates, it frees the Application object, which frees all forms. For objects that are not components, or for components created with a nil owner, be sure to call System::TObject::Free after you are finished with them; otherwise the allocated memory will not be usable until after the application terminates.

Warning: Never explicitly free a component within one of its own event handlers or the event handler of a component it owns or contains. For example, don't free a button, or the form that owns the button, in its OnClick event handler.

To free a form, call its Release method, which destroys the form and releases the memory allocated for it after all its event handlers and those of the components it contains are through executing.

Note: In C++ code, do not use System::TObject::Free to destroy an object. Use the delete keyword.

C++ Examples:

Copy Code

/*
This example demonstrates how to add and delete menu items
to a popup menu at runtime and assign an event handler to
the OnClick event.  Place a TPopupMenu and three buttons on
the form named "AddButton", "EditButton",  and
"DestroyButton" and add OnClick events to all three buttons.
Put the TPopupMenu in the PopupMenu property of the form.
Place the PopupMenuItemsClick procedure in the TForm1 type
declaration so that it can be used as the method call for
the menu item OnClick event.
*/
void __fastcall TForm1::AddButtonClick(TObject *Sender)
{
    const int num_items = 4;
    for (int index = 0; index < num_items; ++index)
    {
        TMenuItem *NewItem = new TMenuItem(PopupMenu1); // create the new item
        PopupMenu1->Items->Add(NewItem);// add it to the Popupmenu
        NewItem->Caption = "Menu Item " + IntToStr(index);
        NewItem->Tag = index;
        NewItem->OnClick = PopupMenuItemsClick;// assign it an event handler
        TNotifyEvent();
    }
}

void __fastcall TForm1::PopupMenuItemsClick(TObject *Sender)
{
    TMenuItem *ClickedItem = dynamic_cast<TMenuItem *>(Sender);
    if (ClickedItem)
    {
        switch (ClickedItem->Tag)
        {
            case 0:
            {
                ShowMessage("first item clicked");
                break;
            }
            case 1:
            {
                ShowMessage("second item clicked");
                break;
            }
            case 2:
            {
                ShowMessage("third item clicked");
                break;
            }
            case 3:
            {
                ShowMessage("fourth item clicked");
                break;
            }
        }
    }
}

/*
To edit or destroy an item, grab its pointer via the Items
property.
*/
void __fastcall TForm1::EditButtonClick(TObject *Sender)
{
    const int index = 1;
    TMenuItem *ItemToEdit = PopupMenu->Items->Items[index];
    ItemToEdit->Caption = "Changed Caption";
}

void __fastcall TForm1::DestroyButtonClick(TObject *Sender)
{
    const int index = 2;
    TMenuItem *ItemToDelete = PopupMenu->Items->Items[index];
    delete ItemToDelete;
}

Delphi Examples:

Copy Code

{
This example demonstrates how to add and delete menu items
to a popup menu at runtime and assign an event handler to
the OnClick event.  Place a TPopupMenu and three buttons on
the form named "AddButton", "EditButton",  and
"DestroyButton" and add OnClick events to all three buttons.
Put the TPopupMenu in the PopupMenu property of the form.
Place the PopupMenuItemsClick procedure in the TForm1 type
declaration so that it can be used as the method call for
the menu item OnClick event.
}

type
  TForm1 = class(TForm)
    AddButton: TButton;
    EditButton: TButton;
    DestroyButton: TButton;
    PopupMenu1: TPopupMenu;
    procedure AddButtonClick(Sender: TObject);
    procedure EditButtonClick(Sender: TObject);
    procedure DestroyButtonClick(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    procedure PopupMenuItemsClick(Sender: TObject);

  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.AddButtonClick(Sender: TObject);
var
  index: Integer;
  NewItem: TMenuItem;
begin
  for index := 0 to 3 do
  begin
    NewItem :=
      TMenuItem.Create(PopupMenu1); // create the new item
    PopupMenu1.Items.Add(NewItem);// add it to the Popupmenu
    NewItem.Caption := 'Menu Item ' + IntToStr(index);
    NewItem.Tag := index;
    NewItem.OnClick :=
      PopupMenuItemsClick; // assign it an event handler
  end;
end;

procedure TForm1.PopupMenuItemsClick(Sender: TObject);
begin
  with Sender as TMenuItem do
  begin
    case Tag of
      0:  ShowMessage('first item clicked');
      1:  ShowMessage('second item clicked');
      2:  ShowMessage('third item clicked');
      3:  ShowMessage('fourth item clicked');
    end;
  end;
end;

{
To edit or destroy an item, grab its pointer via the Items
property.
}
procedure TForm1.EditButtonClick(Sender: TObject);
var
  ItemToEdit: TMenuItem;
begin
  ItemToEdit := PopupMenu.Items[1];
  ItemToEdit.Caption := 'Changed Caption';
end;

procedure TForm1.DestroyButtonClick(Sender: TObject);
var
  ItemToDelete: TMenuItem;
begin
  ItemToDelete := PopupMenu.Items[2];
  ItemToDelete.Free;
end;