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UIPanGestureRecognizer - Only vertical or horizontal

Asked 2011-08-17T23:53:09.007
156

I have a view that has a UIPanGestureRecognizer to drag the view vertically. So in the recognizer callback, I only update the y-coordinate to move it. The superview of this view, has a UIPanGestureRecognizer that will drag the view horizontally, just updating the x-coordinate.

The problem is that the first UIPanGestureRecognizer is taking the event to move the view vertically, so I can not use the superview gesture.

I have tried 

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer
 shouldRecognizeSimultaneouslyWithGestureRecognizer:
                            (UIGestureRecognizer *)otherGestureRecognizer;

and both will work, but I don't want that. I want the horizontally to be detected only if the movement is clearly horizontal. So it would be great if the UIPanGestureRecognizer had a direction property.

How can I achieve this behavior? I find the docs very confusing, so maybe someone can explain it better here.

ios uigesturerecognizer
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2 Answers

227

Just do this for the vertical pan gesture recognizer, it works for me:

- (BOOL)gestureRecognizerShouldBegin:(UIPanGestureRecognizer *)panGestureRecognizer {
    CGPoint velocity = [panGestureRecognizer velocityInView:someView];
    return fabs(velocity.y) > fabs(velocity.x);
}

And for Swift:

func gestureRecognizerShouldBegin(_ gestureRecognizer: UIPanGestureRecognizer) -> Bool {
    let velocity = gestureRecognizer.velocity(in: someView)
    return abs(velocity.y) > abs(velocity.x)
}
answered 2011-12-22T12:27:07.323
51

I figured it out creating a subclass of UIPanGestureRecognizer

DirectionPanGestureRecognizer:

#import <Foundation/Foundation.h>
#import <UIKit/UIGestureRecognizerSubclass.h>

typedef enum {
    DirectionPangestureRecognizerVertical,
    DirectionPanGestureRecognizerHorizontal
} DirectionPangestureRecognizerDirection;

@interface DirectionPanGestureRecognizer : UIPanGestureRecognizer {
    BOOL _drag;
    int _moveX;
    int _moveY;
    DirectionPangestureRecognizerDirection _direction;
}

@property (nonatomic, assign) DirectionPangestureRecognizerDirection direction;

@end

DirectionPanGestureRecognizer.m:

#import "DirectionPanGestureRecognizer.h"

int const static kDirectionPanThreshold = 5;

@implementation DirectionPanGestureRecognizer

@synthesize direction = _direction;

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    [super touchesMoved:touches withEvent:event];
    if (self.state == UIGestureRecognizerStateFailed) return;
    CGPoint nowPoint = [[touches anyObject] locationInView:self.view];
    CGPoint prevPoint = [[touches anyObject] previousLocationInView:self.view];
    _moveX += prevPoint.x - nowPoint.x;
    _moveY += prevPoint.y - nowPoint.y;
    if (!_drag) {
        if (abs(_moveX) > kDirectionPanThreshold) {
            if (_direction == DirectionPangestureRecognizerVertical) {
                self.state = UIGestureRecognizerStateFailed;
            }else {
                _drag = YES;
            }
        }else if (abs(_moveY) > kDirectionPanThreshold) {
            if (_direction == DirectionPanGestureRecognizerHorizontal) {
                self.state = UIGestureRecognizerStateFailed;
            }else {
                _drag = YES;
            }
        }
    }
}

- (void)reset {
    [super reset];
    _drag = NO;
    _moveX = 0;
    _moveY = 0;
}

@end

This will only trigger the gesture if the user starts dragging in the selecte

answered 2011-08-22T15:20:21.780

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