Qt: Why doesn't my button get the signal?

Question

Why didn't the button object get the sigKK() signal when the button was clicked?

When a signal is emitted, can all qt objects receive this signal?

The code is as follows:

class PushButton :  public QPushButton
{
    Q_OBJECT
signals:
    void sigKK();
};

The PushButton class inherits from QPushButton, but doesn't connect signals and slots here. Is this right?

class MainWindow : public QMainWindow
{
    Q_OBJECT    
public:
    explicit MainWindow(){
        resize(400,200);    
        connect(this,SIGNAL(sigKK()),this,SLOT(showRecv1()));   

        button = new PushButton();
        button->setText("Hello,All");
        button->resize(40,15);
        connect(button, SIGNAL(clicked()),this,SLOT(buttonCK()));
        connect(button, SIGNAL(sigKK()),this,SLOT(showRecv2()));
            //**I can connect sigKK signal with showRecv2 slot here ?**** 
        button->show();
    }
    ~MainWindow(){      
    }
signals:
    void sigKK();
public slots:
    void showRecv1(){
        cout<<"recved 1"<<endl;
        resize(100,100);
    }
    void showRecv2(){
        cout<<"recved 2"<<endl;
        button->setText(".....");
    }
    void buttonCK(){
        emit sigKK();
        cout<<"emited"<<endl;
    }
private:
    PushButton *button ; 
};
#endif

Answer 1

When a signal is emitted, can all qt objects receive this signal ?

No. When a signal is emitted it is received only by QObjects with signals or slots connected to it.

Your MainWindow and your PushButton both have a signal with the same name... but they are still different signals. They are completely unrelated to each other. When MainWindow emits sigKK, that has no effect on PushButton's sigKK.

In your example, sigKK seems to be entirely unneccessary. Perhaps you could instead connect clicked() directly to the actions you want to perform?

connect(button, SIGNAL(clicked()),this,SLOT(showRecv1()));
connect(button, SIGNAL(clicked()),this,SLOT(showRecv2()));