“摇一摇”功能实现

1 让当前ViewController 能够成为firstResponder

- (BOOL)canBecomeFirstResponder{

    return YES;

}

2 重载motion相关函数，实现自己的业务逻辑

- (void)motionBegan:(UIEventSubtype)motion withEvent:(UIEvent *)event NS_AVAILABLE_IOS(3_0);

- (void)motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event NS_AVAILABLE_IOS(3_0);

- (void)motionCancelled:(UIEventSubtype)motion withEvent:(UIEvent *)event NS_AVAILABLE_IOS(3_0);

（注：这几个函数与touch相关的几个函数一样，都是UIResponder类的"虚函数"）