ios - UIPanGestureRecognizer的锁定方向

Question

我有一个UIPanGestureRecognizer用来拉视图的。视图从 x = 160，y= 817 开始，当它向上滑动时，我希望它转到 160,284。当它被弹回时，我希望它自动回到起点。到目前为止，这是我的代码：

-(IBAction) dragMe: (UIPanGestureRecognizer *)recognizer {

CGPoint translation = [recognizer translationInView:recognizer.view.superview];

recognizer.view.center = CGPointMake(recognizer.view.center.x, +  recognizer.view.center.y + translation.y);
[recognizer setTranslation:CGPointMake(0, 0) inView:recognizer.view.superview];

if (recognizer.state == UIGestureRecognizerStateEnded) {

    CGPoint velocity = [recognizer velocityInView:recognizer.view.superview];
    CGFloat magnitude = sqrtf((velocity.y * velocity.y));
    CGFloat slideMult = magnitude / 100;
    NSLog(@"magnitude: %f, slideMult: %f", magnitude, slideMult);

    float slideFactor = 0.1 * slideMult; // Increase for more of a slide
    CGPoint finalPoint = CGPointMake(recognizer.view.center.x,
                                     recognizer.view.center.y + (velocity.y * slideFactor));
    finalPoint.x = MIN(MAX(finalPoint.x, 160), recognizer.view.superview.bounds.size.width);
    finalPoint.y = MIN(MAX(finalPoint.y, 284), recognizer.view.superview.bounds.size.height);

    [UIView animateWithDuration:slideFactor*1 delay:0 options:UIViewAnimationOptionCurveEaseOut animations:^{
        recognizer.view.center = finalPoint;
    } completion:nil];



}

}

我不希望用户能够水平移动它，只是垂直移动。