问在iOS中使用滑动手势的滚动效果

EN

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panHandler:)];
    [self.view addGestureRecognizer:pan];

    self.label1.text = @"Mo";
}

- (void)panHandler:(UIPanGestureRecognizer *)sender
{
    if (sender.state == UIGestureRecognizerStateBegan)
    {
        _panLabel = [[UILabel alloc] init];

        // in my example, I'm just going to toggle the value between Mo and Curly
        // you'll presumably set the label contents based upon the direction of the
        // pan (if positive, swiping to the right, grab the "previous" label, if negative
        // pan, grab the "next" label)

        if ([self.label1.text isEqualToString:@"Curly"])
            _newText = @"Mo";
        else
            _newText = @"Curly";

        // set the text

        _panLabel.text = _newText;

        // set the frame to just be off screen

        _panLabel.frame = CGRectMake(self.label1.frame.origin.x + self.containerView.frame.size.width,
                                     self.label1.frame.origin.y, 
                                     self.label1.frame.size.width, 
                                     self.label1.frame.size.height);

        [self.containerView addSubview:_panLabel];

        _originalCenter = self.label1.center; // save where the original label originally was
    }
    else if (sender.state == UIGestureRecognizerStateChanged)
    {
        CGPoint translate = [sender translationInView:self.containerView];

        if (translate.x > 0)
        {
            _panLabel.center = CGPointMake(_originalCenter.x - self.containerView.frame.size.width + translate.x, _originalCenter.y);
            self.label1.center = CGPointMake(_originalCenter.x + translate.x, _originalCenter.y);
        }
        else 
        {
            _panLabel.center = CGPointMake(_originalCenter.x + self.containerView.frame.size.width + translate.x, _originalCenter.y);
            self.label1.center = CGPointMake(_originalCenter.x + translate.x, _originalCenter.y);
        }
    }
    else if (sender.state == UIGestureRecognizerStateEnded || sender.state == UIGestureRecognizerStateFailed || sender.state == UIGestureRecognizerStateCancelled)
    {
        CGPoint translate = [sender translationInView:self.containerView];
        CGPoint finalNewFieldLocation;
        CGPoint finalOriginalFieldLocation;
        BOOL panSucceeded;

        if (sender.state == UIGestureRecognizerStateFailed ||
            sender.state == UIGestureRecognizerStateCancelled)
        {
            panSucceeded = NO;
        }
        else 
        {
            // by factoring in the velocity, we can capture a flick more accurately
            //
            // (by the way, I don't like iOS's velocity, because if you stop moving, it records the velocity
            // prior to stopping the move rather than noting that you actually stopped, so I usually calculate my own, 
            // but I'll leave this as is for purposes of this example)

            CGPoint velocity  = [sender velocityInView:self.containerView];

            if (translate.x < 0)
                panSucceeded = ((translate.x + velocity.x * 0.5) < -(self.containerView.frame.size.width / 2));
            else
                panSucceeded = ((translate.x + velocity.x * 0.5) > (self.containerView.frame.size.width / 2));
        }

        if (panSucceeded)
        {
            // if we succeeded, finish moving the stuff

            finalNewFieldLocation = _originalCenter;
            if (translate.x < 0)
                finalOriginalFieldLocation = CGPointMake(_originalCenter.x - self.containerView.frame.size.width, _originalCenter.y);
            else
                finalOriginalFieldLocation = CGPointMake(_originalCenter.x + self.containerView.frame.size.width, _originalCenter.y);
        }
        else
        {
            // if we didn't, then just return everything to where it was

            finalOriginalFieldLocation = _originalCenter;

            if (translate.x < 0)
                finalNewFieldLocation = CGPointMake(_originalCenter.x + self.containerView.frame.size.width, _originalCenter.y);
            else
                finalNewFieldLocation = CGPointMake(_originalCenter.x - self.containerView.frame.size.width, _originalCenter.y);
        }

        // animate the moving of stuff to their final locations, and on completion, clean everything up

        [UIView animateWithDuration:0.3
                              delay:0.0 
                            options:UIViewAnimationOptionCurveEaseOut
                         animations:^{
                             _panLabel.center = finalNewFieldLocation;
                             self.label1.center = finalOriginalFieldLocation;
                         }
                         completion:^(BOOL finished) {
                             if (panSucceeded)
                                 self.label1.text = _newText;
                             self.label1.center = _originalCenter;
                             [_panLabel removeFromSuperview];
                             _panLabel = nil; // in non-ARC, release instead
                         }
         ];
    }
}