How to initiate a gesture recognizer when a gesture is already active?

Question

I have a Subview A(self.thumbnailImageView) added to my superview. I have added a UILongPressGestureRecognizer and UISwipeGestureRecognizer to my subview A.

[self addLongPressGestureRecognizerForPreviewCell:self.thumbnailImageView];

[self addSwipeUpGestureRecognizerForImageView:self.thumbnailImageView];

Now in the handler methods, when the UILongPressGestureRecognizer state begins, i add a Subview B(bigPreviewImage) to my superview(self.view).

-(void)tapGesture:(UILongPressGestureRecognizer *)recognizer{

 if (recognizer.state == UIGestureRecognizerStateBegan)
 {
    // Long press detected, start the timer
    [self showPreviewImage:recognizer];
 }
 else if(recognizer.state == UIGestureRecognizerStateEnded)
 {
    [self hidePreviewImage];
 }
}

-(void)showPreviewImage:(UILongPressGestureRecognizer *)recognizer{

    UIImageView *bigPreviewImage = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Desktop"]];

    bigPreviewImage.frame = CGRectMake(self.thumbnailImageView.frame.origin.x - 50.0, self.thumbnailImageView.frame.origin.y + self.thumbnailImageView.frame.size.height + 10.0, 300.0, 250.0);
    bigPreviewImage.tag = 10000;//200.0 & 125.0
    [bigPreviewImage setUserInteractionEnabled:YES];

    [self.view addSubview:bigPreviewImage];
}

Now once the UILongPressGestureRecognizer is active and the user with his finger still pressing the Subview A, If the user swipes up the screen, i want the SwipeGestureRecognizer to get initiated. But the same is not happening. How to initiate a gesture recognizer when a gesture is already active?

I have implemented the shouldRecognizeSimultaneouslyWithGestureRecognizer method but still the swipe up gesture method is not called. Please let me know if i am missing something.

Pradeep Reddy Kypa Pradeep Reddy Kypa · Accepted Answer · 2016-05-25T10:04:25

Got it!!!

We dont need a separate Swipe Gesture Recognizer. The different states in Long Press Gesture Recognizer can be used to handle this scenario.

Long Press Gesture has different states Like UIGestureRecognizerStateBegan, UIGestureRecognizerStateChanged and UIGestureRecognizerStateEnded.

UIGestureRecognizerStateBegan gets called as soon as you long press the subview.
UIGestureRecognizerStateChanged gets called when the user tries to move the finger .
UIGestureRecognizerStateEnded gets called when the user lifts the finger from the touch point.

-(void)longPressGestureForPreviewImageView:(UILongPressGestureRecognizer *)recognizer{

    if (recognizer.state == UIGestureRecognizerStateBegan)
    {
        // Long press detected, start the timer
        [self showPreviewImage:recognizer];
    }
    else if(recognizer.state == UIGestureRecognizerStateChanged)
    {
        NSLog(@"Swipe up");

        if ([self.thumbnailImageView.gestureRecognizers containsObject:recognizer]) {
            [self.thumbnailImageView removeGestureRecognizer:recognizer];
        }
    }
    else if(recognizer.state == UIGestureRecognizerStateEnded)
    {
        [self hidePreviewImage];
    }

So we can use the Gesture Delegate methods to handle the swipe along with a Long Press Gesture Recognizer.

How to initiate a gesture recognizer when a gesture is already active?

1 Answers