Problems using UIPanGestureRecognizer in UITableViewCell

Question

I'm trying to implement a UIPanGestureRecognizer in my UITableViewController to use for a swipe to delete animation. Similar to the swipe to delete used in the Clear app, where if you swipe a UITableViewCell in left or right the cell moves and gets deleted.

I have tried implementing this in my UITableViewCell subclass but it never seems to receive the event.

This is the code I put in my UITableViewCell subclass to try this functionality. In my init method

UIGestureRecognizer *recognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
    recognizer.delegate = self;
    [self addGestureRecognizer:recognizer];

and then the methods to handle it:

- (BOOL)gestureRecognizerShouldBegin:(UIPanGestureRecognizer *)gestureRecognizer {
CGPoint translation = [gestureRecognizer translationInView:self.superview];
//might have to change view to tableView
//check for the horizontal gesture
if (fabsf(translation.x) > fabsf(translation.y)) {
    return YES;
    NSLog(@"Panning");
}
return NO;
}

- (void)handlePan:(UIPanGestureRecognizer *)recognizer {
if (recognizer.state == UIGestureRecognizerStateBegan) {
    //if the gesture has just started record the center location
    NSLog(@"handlePan");
    _originalCenter = self.center; //Declared as a CGPoint at the top of my TableViewCell
}

if (recognizer.state == UIGestureRecognizerStateChanged) {
    //translate the center (aka translate from the center of the cell)
    CGPoint translation = [recognizer translationInView:self];
    self.center = CGPointMake(_originalCenter.x + translation.x, _originalCenter.y);
    // determine whether the item has been dragged far enough to delete/complete

}

if (recognizer.state == UIGestureRecognizerStateEnded) {
    // the frame this cell would have had before being dragged
    CGRect originalFrame = CGRectMake(0, self.frame.origin.y, self.bounds.origin.x, self.bounds.size.height);
    [UIView animateWithDuration:0.2 animations:^{
        self.frame = originalFrame;}
     ];
}
}

The Cells don't move at all though. Not really sure what's going on here

Answer 1

If you don't want the cell's swipe gesture to happen simultaneously with the table view scroll gesture, then add a pan gesture to your cell and make it a delegate:

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

And implement the following delegate method to only start if the pan is horizontal:

#pragma mark - UIGestureRecognizerDelegate

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
{
    // note: we might be called from an internal UITableViewCell long press gesture

    if ([gestureRecognizer isKindOfClass:[UIPanGestureRecognizer class]]) {

        UIPanGestureRecognizer *panGestureRecognizer = (UIPanGestureRecognizer*)gestureRecognizer;
        UIView *cell = [panGestureRecognizer view];
        CGPoint translation = [panGestureRecognizer translationInView:[cell superview]];

        // Check for horizontal gesture
        if (fabs(translation.x) > fabs(translation.y))
        {
            return YES;
        }

    }

    return NO;
}

Swift3 ..

override func awakeFromNib() {
    super.awakeFromNib()
    // do not use, say, layoutSubviews as layoutSubviews is called often
    let p = UIPanGestureRecognizer(target: self, action: #selector(yourPan))
    p.delegate = self
    contentView.addGestureRecognizer(p)
    }
}

override func gestureRecognizerShouldBegin(_ g: UIGestureRecognizer) -> Bool {
    if (g.isKind(of: UIPanGestureRecognizer.self)) {
        let t = (g as! UIPanGestureRecognizer).translation(in: contentView)
        let verticalness = abs(t.y)
        if (verticalness > 0) {
            print("ignore vertical motion in the pan ...")
            print("the event engine will >pass on the gesture< to the scroll view")
            return false
        }
    }
    return true
}

Answer 2

You need the following method in order for the gesture to be detected in sync with the scrollView's panGesture:

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
   return YES; //otherGestureRecognizer is your custom pan gesture
}

Remember to set the panGesture.delegate to your viewController. (Updated with OlivaresF's comment.)