T qobject_cast ( QObject * object )
Returns the given object cast to type T if the object is of type T (or of a subclass); otherwise returns 0. If object is 0 then it will also return 0.
The class T must inherit (directly or indirectly) QObject and be declared with the Q_OBJECT macro.
A class is considered to inherit itself.
Example:
QObject *obj = new QTimer; // QTimer inherits QObject
QTimer *timer = qobject_cast<QTimer *>(obj);
// timer == (QObject *)obj
QAbstractButton *button = qobject_cast<QAbstractButton *>(obj);
// button == 0
Q:看了Assistant之后，仍有疑问，请朋友帮忙解答下吧，先谢过！
在Example中的第二个QAbstractButton *button为什么返回的
button == 0 呢？
有人说“转换的对象类型必须是obj的父类或者同级才能得到正确的结果，同时还得注意Q_OBJECT宏定义。”
那么是否可以认为 QObject <- QWidget <- QAbstractButton ;
QObject <- QTimer ; 由于QAbstractButton 与 QTimer不同级所以在Example中的第二个返回的
button == 0 ？
