_panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlerPanGesture:)];
    _panGestureRecognizer.delegate = self;
    _panGestureRecognizer.maximumNumberOfTouches = 2;
    _panGestureRecognizer.minimumNumberOfTouches = 2;
    [self.view addGestureRecognizer:_panGestureRecognizer];

- (void)handlerPanGesture:(UIPanGestureRecognizer *)recognizer
{
    if ((recognizer.state == UIGestureRecognizerStateBegan) ||
        (recognizer.state == UIGestureRecognizerStateChanged))
    {
        CGPoint offset = [recognizer translationInView:self.view];
        CGRect frame = self.rightViewController.view.frame;
        frame.origin.x += offset.x;
        if (frame.origin.x >= 0 && frame.origin.x <= kScreenWidth)
        {
            self.rightViewController.view.frame = frame;
        }
        
        [recognizer setTranslation:CGPointZero inView:self.view];
    }
    else if (recognizer.state == UIGestureRecognizerStateEnded)
    {
        BOOL isVisible = self.rightViewController.view.frame.origin.x < kScreenWidth / 2;
        [self showRightView:isVisible];
    }
}

typedef NS_ENUM(NSInteger, UIGestureRecognizerState) {
    UIGestureRecognizerStatePossible,   // the recognizer has not yet recognized its gesture, but may be evaluating touch events. this is the default state
    
    UIGestureRecognizerStateBegan,      // the recognizer has received touches recognized as the gesture. the action method will be called at the next turn of the run loop
    UIGestureRecognizerStateChanged,    // the recognizer has received touches recognized as a change to the gesture. the action method will be called at the next turn of the run loop
    UIGestureRecognizerStateEnded,      // the recognizer has received touches recognized as the end of the gesture. the action method will be called at the next turn of the run loop and the recognizer will be reset to UIGestureRecognizerStatePossible
    UIGestureRecognizerStateCancelled,  // the recognizer has received touches resulting in the cancellation of the gesture. the action method will be called at the next turn of the run loop. the recognizer will be reset to UIGestureRecognizerStatePossible
    
    UIGestureRecognizerStateFailed,     // the recognizer has received a touch sequence that can not be recognized as the gesture. the action method will not be called and the recognizer will be reset to UIGestureRecognizerStatePossible
    
    // Discrete Gestures – gesture recognizers that recognize a discrete event but do not report changes (for example, a tap) do not transition through the Began and Changed states and can not fail or be cancelled
    UIGestureRecognizerStateRecognized = UIGestureRecognizerStateEnded // the recognizer has received touches recognized as the gesture. the action method will be called at the next turn of the run loop and the recognizer will be reset to UIGestureRecognizerStatePossible
};

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch
{
    if ([touch.view isKindOfClass:[UIControl class]])
    {
        return NO;
    }
    
    return YES;
}