delphi中 formclose的事件 action:=cafree form:=nil分别是什么意思？

MDI子窗体关闭时用到的

(以下摘自Delphi的帮助)

caNone The form is not allowed to close, so nothing happens.

caHide The form is not closed, but just hidden. Your application can still access a hidden form.

caFree The form is closed and all allocated memory for the form is freed.

caMinimize The form is minimized, rather than closed. This is the default action for MDI child forms.

Action := caFree; Form关闭后释放占用的内存

The form is closed and all allocated memory for the form is freed.

Form关闭并释放所有分配给Form的内存。

Form := nil; Form对象指向空地址