Passing vertical scrolling gesture to UITableView below

Question

(edited for clarity)

I have a UITableView. On top of that is a UIView with a Pan gesture attached. This Pan swipes left and right to change the underlying table. I use the pan gesture's action method to move the table. That working fine.

However, the UIView & its Pan gesture interferes with up/down scrolling the UITableView. How can I send the up/down scrolling to the table and keep the left-right on the view's area?

 ---------------------------------------
 |                                     |
 |             ----------------------  |
 |             |                    |  |
 |             |                    |  |
 |             |                    |  |
 | UITableView |                    |  |
 |             |        UIView      |  |
 |             |          +         |  |
 |             |       PanGesture   |  |
 |             |                    |  |
 |             |                    |  |
 |             |                    |  |
 |             |                    |  |
 |             ----------------------  |
 |                                     |
 |                                     |
 ---------------------------------------

The method triggered by the Pan gesture is like this

 -(void)move:(UIPanGestureRecognizer*)sender
 {
     CGPoint translatedPoint = [(UIPanGestureRecognizer*)sender translationInView:self.view];
     float xTest = fabsf(translatedPoint.x);
     float yTest = fabsf(translatedPoint.y);
     if ( xTest>yTest)
     {
         // Move table view left-right.. this works
     } else
     {
         // Send up-down scrolling gesture to table view????? How to?
     }
 }

Answer 1

I just solved a similar problem, except it was for vertical pans instead of horizontal ones. I'm not 100% sure about your use case, so this may not be what your looking for, but it may lead you in the right direction.

I sub-classed UIPanGestureRecognizer, and implemented the touchesMoved method, and checked to see whether the gesture had a larger horizontal or vertical change. Below is a snippet. The credit belongs to a different stackoverflow post, but I cannot find the link at the moment. (Sorry in advance for the poor formatting, first time posting)

-(void)touchesMoved:(NSSet*) touches withEvent:(UIEvent *)event
{
[super touchesMoved:touches withEvent:event];
if(self.state == UIGestureRecognizerStateFailed) return;
CGPoint currentPoint = [[touches anyObject] locationInView:self.view];
CGPoint prevPoint = [[touches anyObject] previousLocationInView:self.view];
moveX += prevPoint.x - currentPoint.x;
moveY += prevPoint.y - currentPoint.y;
if(!drag) {
    if(abs(moveY) > abs(moveX))
        drag = YES;
    else
        self.state = UIGestureRecognizerStateFailed;
}
}

-(void)reset
{
[super reset];
drag = NO;
moveX = 0;
moveY = 0;
}

In my parent view controller, which I believe would be the UITableView in this case, I also implemented the following. I think in your case, you'd want to return no if it's a horizontal pan.

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

Let me know if any of this is unclear.

Good Luck!

Answer 2

UIGestureRecognizer has a property that prevents recognized gestures from forwarding their events to the view-hierachy - sounds as if that was the right option for you. Try that and set it towards NO on your gesture recognisers in question.

cancelsTouchesInView

A Boolean value affecting whether touches are delivered to a view when a gesture is recognized.

@property(nonatomic) BOOL cancelsTouchesInView

Discussion

When this property is YES (the default) and the receiver recognizes its gesture, the touches of that gesture that are pending are not delivered to the view and previously delivered touches are cancelled through a touchesCancelled:withEvent: message sent to the view. If a gesture recognizer doesn’t recognize its gesture or if the value of this property is NO, the view receives all touches in the multi-touch sequence.

Available in iOS 3.2 and later.

From UIGestureRecognizer reference.