Scrolling with two fingers with a UIScrollView

Question

I have an app where my main view accepts both touchesBegan and touchesMoved, and therefore takes in single finger touches, and drags. I want to im

Answer 1

Bad news: iPhone SDK 3.0 and up, don't pass touches to -touchesBegan: and -touchesEnded: **UIScrollview**subclass methods anymore. You can use the touchesShouldBegin and touchesShouldCancelInContentView methods that is not the same.

If you really want to get this touches, have one hack that allow this.

In your subclass of UIScrollView override the hitTest method like this:

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {

  UIView *result = nil;
  for (UIView *child in self.subviews)
    if ([child pointInside:point withEvent:event])
      if ((result = [child hitTest:point withEvent:event]) != nil)
        break;

  return result;
}

This will pass to you subclass this touches, however you can't cancel the touches to UIScrollView super class.

Answer 2

Kenshi's answer in Swift 4

for gestureRecognizer: UIGestureRecognizer in self.gestureRecognizers! {
    if (gestureRecognizer is UIPanGestureRecognizer) {
        let panGR = gestureRecognizer as? UIPanGestureRecognizer
        panGR?.minimumNumberOfTouches = 2
    }
}

Answer 3

What I do is have my view controller set up the scroll view:

[scrollView setCanCancelContentTouches:NO];
[scrollView setDelaysContentTouches:NO];

And in my child view I have a timer because two-finger touches usually start out as one finger followed quickly by two fingers.:

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    // Hand tool or two or more touches means a pan or zoom gesture.
    if ((selectedTool == kHandToolIndex) || (event.allTouches.count > 1)) {
        [[self parentScrollView] setCanCancelContentTouches:YES];
        [firstTouchTimer invalidate];
        firstTouchTimer = nil;
        return;
    }

    // Use a timer to delay first touch because two-finger touches usually start with one touch followed by a second touch.
    [[self parentScrollView] setCanCancelContentTouches:NO];
    anchorPoint = [[touches anyObject] locationInView:self];
    firstTouchTimer = [NSTimer scheduledTimerWithTimeInterval:kFirstTouchTimeInterval target:self selector:@selector(firstTouchTimerFired:) userInfo:nil repeats:NO];
    firstTouchTimeStamp = event.timestamp;
}

If a second touchesBegan: event comes in with more than one finger, the scroll view is allowed to cancel touches. So if the user pans using two fingers, this view would get a touchesCanceled: message.

Answer 4

In iOS 3.2+ you can now achieve two-finger scrolling quite easily. Just add a pan gesture recognizer to the scroll view and set its maximumNumberOfTouches to 1. It will claim all single-finger scrolls, but allow 2+ finger scrolls to pass up the chain to the scroll view's built-in pan gesture recognizer (and thus allow normal scrolling behavior).

UIPanGestureRecognizer *panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(recognizePan:)];
panGestureRecognizer.maximumNumberOfTouches = 1;
[scrollView addGestureRecognizer:panGestureRecognizer];
[panGestureRecognizer release];

Answer 5

Check out my solution:

#import “JWTwoFingerScrollView.h”

@implementation JWTwoFingerScrollView

- (id)initWithCoder:(NSCoder *)coder {
    self = [super initWithCoder:coder];
    if (self) {
        for (UIGestureRecognizer* r in self.gestureRecognizers) {
            NSLog(@“%@”,[r class]);
            if ([r isKindOfClass:[UIPanGestureRecognizer class]]) {
                [((UIPanGestureRecognizer*)r) setMaximumNumberOfTouches:2];
                [((UIPanGestureRecognizer*)r) setMinimumNumberOfTouches:2];
            }
        }
    }
    return self;
}

-(void)firstTouchTimerFired:(NSTimer*)timer {
    [self setCanCancelContentTouches:NO];
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    [self setCanCancelContentTouches:YES];
    if ([event allTouches].count == 1){
        touchesBeganTimer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(firstTouchTimerFired:) userInfo: nil repeats:NO];
        [touchesBeganTimer retain];
        [touchFilter touchesBegan:touches withEvent:event];
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    [touchFilter touchesMoved:touches withEvent:event];
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@“ended %i”,[event allTouches].count);
    [touchFilter touchesEnded:touches withEvent:event];
}

-(void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
    NSLog(@“canceled %i”,[event allTouches].count);
    [touchFilter touchesCancelled:touches withEvent:event];
}

@end

It does not delays the first touch and does not stop when the user touches with two fingers after using one. Still it allows to cancel a just started one touch event using a timer.

Answer 6

I put this in the viewDidLoad method and this accomplishes the scroll view handling the two touch pan behavior and another pan gesture handler handling the one touch pan behavior -->

scrollView.panGestureRecognizer.minimumNumberOfTouches = 2

let panGR = UIPanGestureRecognizer(target: self, action: #selector(ViewController.handlePan(_:)))
panGR.minimumNumberOfTouches = 1
panGR.maximumNumberOfTouches = 1

scrollView.gestureRecognizers?.append(panGR)

and in the handlePan method which is a function attached to the ViewController there is simply a print statement to verify that the method is being entered -->

@IBAction func handlePan(_ sender: UIPanGestureRecognizer) {
    print("Entered handlePan numberOfTuoches: \(sender.numberOfTouches)")
}

HTH