Question

I’m trying to build a GestureRecognizer to drag a UIView from right to left. If the user drag the View to the half of the screen, the View will be automatically dragged into the left corner to discard it, but if the user do not drag up to half the screen it will return to the corner right of the screen.
Little lost here, any tutorials or something?
Thanks

EDIT : Heres some code, its a UIImageView, inside a UIScrollView, i need to drag the entire scroll or just the image inside it :

_myScroll = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.window.bounds.size.width, self.window.bounds.size.height)]; [_myScroll setContentSize:CGSizeMake(self.window.bounds.size.width , 1300)];

_tutorial = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.window.bounds.size.width, 1300)]; [_tutorial setImage:[UIImage imageNamed:@"Default"]];
_tutorial.contentMode = UIViewContentModeScaleAspectFit; [_myScroll addSubview:_tutorial];

_tutorial.userInteractionEnabled = YES;
    UIPanGestureRecognizer * recognizer = [[UIPanGestureRecognizer alloc]initWithTarget:_tutorial action:@selector(handlePan:)]; 
 [_tutorial addGestureRecognizer:recognizer];

    [self.window addSubview:_myScroll];

And the method i try to drag the UIImageView

- (IBAction)handlePan:(UIPanGestureRecognizer *)recognizer {

    CGPoint translation = [recognizer translationInView:_myScroll];
    recognizer.view.center = CGPointMake(recognizer.view.center.x + translation.x,
                                         recognizer.view.center.y + translation.y);
    [recognizer setTranslation:CGPointMake(0, 0) inView:_myScroll];

}

Answer 1

Have a look over here. This is a UIGestureRecognizer tutorial which will give you the basics to handle pinch and pan gestures. Once you’ve learnt the basics, it’s really easy to accomplish what you want. All you need is to check the position of the view once the pan is completed to send it to the correct position. Have a look at this other tutorial on UIScrollViews, it may help you find your way through the second part.

Both tutorials come from raywenderlich.com, probably the most useful iOS tutorials site I know.

---

Here is some code on your handlePan: method you can work on :

- (IBAction)handlePan:(UIPanGestureRecognizer *)recognizer {

    CGPoint translation = [recognizer translationInView:_myScroll];

    recognizer.view.center = CGPointMake(recognizer.view.center.x + translation.x,
                                         recognizer.view.center.y + translation.y);

    if (recognizer.state == UIGestureRecognizerStateEnded) {

        // Check here for the position of the view when the user stops touching the screen

        // Set "CGFloat finalX" and "CGFloat finalY", depending on the last position of the touch

        // Use this to animate the position of your view to where you want
        [UIView animateWithDuration: aDuration
                              delay: 0 
                            options: UIViewAnimationOptionCurveEaseOut 
                         animations:^{
            CGPoint finalPoint = CGPointMake(finalX, finalY);
            recognizer.view.center = finalPoint; } 
                         completion:nil];
    }


    [recognizer setTranslation:CGPointMake(0, 0) inView:_myScroll];

}

I won’t give you the perfect answer here, you’ll have to work on the code to find a way to make it work as you want it to.

Here is one last tip. You can do some kind of “smooth” animation by using a slideFactor. It will help your animation being more “realistic”. Work on this code, that you add right at the beginning of the “if”:

CGPoint velocity = [recognizer velocityInView:self.view];
CGFloat magnitude = sqrtf((velocity.x * velocity.x) + (velocity.y * velocity.y));
CGFloat slideMult = magnitude / 200;

float slideFactor = 0.1 * slideMult; // Increase for more slide

Then in UIView animateWithDuration:, use slideFactor as the duration.