Method to make UIGestureRecognizer fail after being recognized?

8
votes

I have a question that might seem basic but can't figure it out.

Basic question is: how do I programmatically put a gesturerecognizer into fail state from handler, while it's in UIGestureRecognizerStateBegan or UIGestureRecognizerStateChanged?

More detailed explanation: I have a long press gesture recognizer for UIView inside a UIScrollView. I have made 

-(BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer 
shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
    return YES;
}

because else I can't get scroll view to scroll once user puts their finger down at the view. It's basic touch like safari, where you hold finger down on a link, which highlights the link, but scroll up or down - then link is unhighlighted and scrollview moves.

I can get this mostly working right now since both gestures are being recognized, but it would be better if I can detect movement in longpress gesturerecognizer's StateChanged, and if it's more than 20 pixels or so, just programmatically make longpress fail.

Is this possible to do? Or am I digging at a wrong spot?

3
iosuiscrollviewuigesturerecognizer

3 Answers

6
votes

Another question that I found right after I posted the question..

Here's what I do in the gesture recognizer handler now:

else if (sender.state == UIGestureRecognizerStateChanged) {
    CGPoint newTouchPoint = [sender locationInView:[self superview]];

    CGFloat dx = newTouchPoint.x - initTouchPoint.x;
    CGFloat dy = newTouchPoint.y - initTouchPoint.y;
    if (sqrt(dx*dx + dy*dy) > 25.0) {
        sender.enabled = NO;
        sender.enabled = YES;
    }
}

So if finger moves more than 25 pixels in any direction, setting enabled property to NO will make the recognizer fail. So this will accomplish what I want!

4
votes

If it is a UILongPressGestureRecognizer, just set its allowableMovement property.

UILongPressGestureRecognizer* recognizer = [your recognizer];
recognizer.allowableMovement = 25.0f;
2
votes

According to the documentation you can subclass you gesture recogniser:

In YourPanGestureRecognizer.m:

#import "YourPanGestureRecognizer.h"

@implementation YourPanGestureRecognizer

- (void) cancelGesture {
    self.state=UIGestureRecognizerStateCancelled;
}

@end

In YourPanGestureRecognizer.h:

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

@interface NPPanGestureRecognizer: UIPanGestureRecognizer

- (void) cancelGesture;

@end

Now you can call if from anywhere

YourPanGestureRecognizer *panRecognizer = [[YourPanGestureRecognizer alloc] initWithTarget:self action:@selector(panMoved:)];
[self.view addGestureRecognizer:panRecognizer];
[...]
-(void) panMoved:(YourPanGestureRecognizer*)sender {
    [sender cancelGesture]; // This will be called twice
}

Ref: https://developer.apple.com/documentation/uikit/uigesturerecognizer?language=objc