qobject_ Cast usage

qobject_cast() Dynamic transformation QObject The type of the class .

T qobject_cast ( QObject * object ) 
 This method returns object Downward transformation T, If the transformation is not successful, return 0, If the incoming object Itself is 0 Then return to 0

Example ：

QObject *obj = new QTimer;          // QTimer inherits QObject
QTimer *timer = qobject_cast<QTimer *>(obj);
  // timer == (QObject *)obj
QAbstractButton *button = qobject_cast<QAbstractButton *>(obj);
  // button == nullptr

Usage restriction :
T Type must inherit from QObject
There must be... In the declaration Q_OBJECT macro .

usage –sender（） function

QPushButton *button_tmp=qobject_cast<QPushButton *>(sender());

When one Object emit One signal When , It's a sender, The system will record who is currently emit Out of this signal Of , So you are corresponding slot You can pass through sender() Get who is currently invoke Your slot, The corresponding is QObject->d->sender.