c++ - QKeyEvent in my app does not work -

i want program retro snaker responds keyevents, here's code:

paint.h

#ifndef paint_h #define paint_h #include<qwidget> #include<qpaintevent> #include<qkeyevent> #include<qtimer>  class paint:public qwidget { q_object public:     paint(qwidget*parent=0);     ~paint(); protected:     void paintevent(qpaintevent* );     void keypress(qkeyevent* keyevent); public slots:     void autorun(); private:     int snake[100][2];     int length;     qtimer *timer;     int flag; }; #endif 

paint.cpp

#include"paint.h" #include<qtgui>  paint::paint(qwidget*parent):qwidget(parent) { flag=1; snake[0][0]=45; snake[0][1]=45; length=4; timer=new qtimer; timer->start(1000); connect(timer,signal(timeout()),this,slot(autorun())); }  paint::~paint(){}  void paint::paintevent(qpaintevent* ) { qpainter p(this); p.setwindow(0,0,810,810); qrectf border(45-20,45-20,16*45+40,16*45+40); qrectf inter(45,45,16*45,16*45); p.setpen(qt::nopen); p.setbrush(qbrush(qt::darkmagenta,qt::solidpattern)); p.drawrect(border); p.setbrush(qbrush(qt::gray,qt::solidpattern)); p.drawrect(inter);// p.setpen(qt::nopen); for(int i=45;i<=17*45;i+=45) {     p.drawline(45,i,17*45,i);     p.drawline(i,45,i,17*45); } p.setpen(qpen(qt::darkgray,1,qt::solidline,qt::roundcap,qt::roundjoin)); //  for(int i=0;i<length;++i) {     qrectf snakebody(snake[0][0],snake[0][1],45,45);     p.setbrush(qbrush(qt::red));     p.drawrect(snakebody); } } void paint::keypress(qkeyevent* keyevent) { qdebug()<<"key"<<endl; switch(keyevent->key()) {     case qt::key_up:         snake[0][1]=45;         break;     case qt::key_down:         snake[0][1]=720;         break;     case qt::key_left:         snake[0][0]=45;         break;     case qt::key_right:         snake[0][1]=720;         break;     case qt::key_q:         qdebug()<<"q"<<endl;         break; } } void paint::autorun() { snake[0][1]+=45; if(snake[0][1]>720) {     snake[0][1]=45;     snake[0][0]+=45;     if(snake[0][0]>720)     {         snake[0][0]=45;     } } update(); } 

focus on keypress() function, wonder function not connect anything, work? didn't, not know how activate it. need else?

http://qt-project.org/doc/qt-4.8/qwidget.html#keypressevent. need override keypressevent, not create keypress function of own.

so, change

void keypress(qkeyevent* keyevent); 

to

void keypressevent(qkeyevent* keyevent)