[qt] meta object system

The meta object system consists of three parts ：

QObject Base class ： The base class of all classes that use the meta object system

Q_OBJECT macro ： Enable classes to use the properties of meta objects , Such as dynamic properties 、 Signals and slots, etc

MOC： Cloud object compiler , For each QObject Subclasses of provide the necessary code to implement the characteristics of the meta object system

besides , Meta objects also provide the following functions ：

• QObject::metaObject() function

         return QMetaObject—— Class associated meta objects , It contains some interface functions for accessing meta objects , for example QMetaObject::className() function , You can return the name string of the class .

• QMetaObject::newInstance() function

         Create a new instance of the class

• QObject::inherits(const char* className) function

        Judge whether an object instance is named className Class or QObject An instance of a subclass of , for example ：

QTimer *timer=new QTimer;
timer->inherits("QTimer");   //true
timer->inherits("QObject");  //true
timer->inherits("QAbstractButton");    //false

• QObject::tr() and QObject::trUtf8() function

        Translate string , For multilingual interface design

• QObject::setProperty(const QString &name,value) and QObject::property(const QString &name) function

         Used to pass the attribute name , Set and get attribute values dynamically , for example ：

QPerson p;
p->setProperty("name"," Xiao Ming ");
p->property("name").toString();// The return is " Xiao Ming "

• qobject_cast<T *>(className) Coercive transformation

        Can be className class , Cast to its base class , for example ：

QObject *obj=new QMyWidget;
QWidget *widget=qobject_cast<QMyWidget*>(obj);

Usually with sender() Function coordination , To cast the obtained signaled class into its base class , Easy to operate .