UIPanGestureRecognizer.maximumNumberOfTouches not respected in nested scroll views?

Question

I have a root UIScrollView that only scrolls vertically, this scrollview represents rows in my jagged grid. I have configured this scroll view's pan gesture recognizer for two touches for both minimum and maximum number of touches requires.

Inside this scrollview I have one or more UIScrollView instances that only scrolls horizontally, these scrollviews each represent a single row in my jagged grid view. I have configured the pan gesture recognizers for all of these scroll views for one touch minimum, and two touches maximum.

So far it works, I get a nice jagged grid view where I can scroll vertically between rows, and horizontally to scroll each row independently. I have intentionally set to minimum number of touches as 2, as not to inter fear with scrolling if I add fro example a UITableView as a subview for any of cell within this jagged grid view (cell == a position defined by a row and column in that row).

Using a UITableView as a cell works, the table view works as expected that is. But scrolling with two fingers also scrolls inside the table view, not at the root scroll view for vertically scrolling between rows.

I have tried configuring the table views pan gesture recognizer to allow a maximum of one touches, in hope that two finger touches would be ignored. This does not work, the maximumNumberOfTouches property of the table view's pan gesture recognizer seams to be ignored.

What could I have done wrong?

A screen shot displaying the layout to clarify what I have done:

Answer 1

Try this link and pay attention to how they solve nested views.

Remember the best Practices for Handling Multitouch Events:

When handling events, both touch events and motion events, there are a few recommended techniques and patterns you should follow.

• Always implement the event-cancellation methods.

In your implementation, you should restore the state of the view to what it was before the current multitouch sequence, freeing any transient resources set up for handling the event. If you don’t implement the cancellation method your view could be left in an inconsistent state. In some cases, another view might receive the cancellation message.

• If you handle events in a subclass of UIView, UIViewController, or (in rare cases) UIResponder,

  • You should implement all of the event-handling methods (even if it is a null implementation).

  • Do not call the superclass implementation of the methods.

• If you handle events in a subclass of any other UIKit responder class,

  • You do not have to implement all of the event-handling methods.

  • But in the methods you do implement, be sure to call the superclass implementation. For example,

[super touchesBegan:theTouches withEvent:theEvent];

• Do not forward events to other responder objects of the UIKit framework.

The responders that you forward events to should be instances of your own subclasses of UIView, and all of these objects must be aware that event-forwarding is taking place and that, in the case of touch events, they may receive touches that are not bound to them.

• Custom views that redraw themselves in response to events should only set drawing state in the event-handling methods and perform all of the drawing in the drawRect: method.

• Do not explicitly send events up the responder (via nextResponder); instead, invoke the superclass implementation and let the UIKit handle responder-chain traversal.

Answer 2

But don't you try some tricks rather than implementing all such changes :

1) By Default, disable the scrolling of the TableView when the view is created.

2) Once the view gets generated, Recognize the gestures whether its Scrolling using single or multiple touches, if user touch the Child Scrollview.Look out the tag ,based on gestures, you can enable the Scrolling of Tableview.

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
   //Get the tag of ScrollView 
   // Check for the Parent as well as Child SCrollview.
   // If its child, just enable the scrolling of tableView.
}

- (void)tapAction:(UIGestureRecognizer *)gestureRecognizer
{

//  CGPoint *poit = [Tile locationInView:gestureRecognizer.view];
/// [[[gestureRecognizers.view] objectAtIndex:0] removeFromSuperview];
//  imageContent = [[UIImageView alloc]initWithFrame:CGRec  tMake(0, 0, 200, 250)];
//  [imageContent setImage:[UIImage imageNamed:@"Default.png"]];

    NSLog(@"You tapped @ this :%d",gestureRecognizer.view.tag);
    //Regonize the gestures
}

There may be some unnecessary code since, there is no code snippet with your question.I gave a try & showed a trick if that could work for you & solve the problem. ;)

Answer 3

TableViews on Scroll views are generally not a great idea. When a TableView receives the touches, even if doesn't need to do anything with it, it won't send them to it's superView.

You might wanna try either of these 2 things:

1. In your TableView you should send the touches to your superView manually and let them handle them appropriately. I've seen this method being used in one of my side-projects but I'm not able to post an example of it at this time.

2. The second thing might be easier to implement. Since TableView is a subclass of ScrollView you can call upon the delaysContentTouches of those TableViews. This property will delay the touch-down even on that TableView until it can determine if scrolling is the intent, as is written in the AppleDocs: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIScrollView_Class/Reference/UIScrollView.html#//apple_ref/occ/cl/UIScrollView

Let me know if either of the 2 ways works for you, I'm quite curious about this subject generally.

Answer 4

Multiple scrolling tends to get tricky, and I don't for sure, but I think Apple does not encourage this. Even so, I still think it's possible. It may be that vertical scrolling on the table view gets mixed with the scroll view vertical scrolling or something else.

Try checking if the delegates for the gesture recognizers are correctly set. Another way around this is: - having a Scroll view with buttons, from which you can open popovers with custom controllers (insert there whatever you want). - create a big UITableViewController and setting the cell's contents as scrollviews etc. I think you could get the same result.

My advice is not to get stuck on just one method, when there could be others more simpler and more intuitive.