Disable other UIImageViews when one UIImageView is touched - cocoa-touch

Question

i've 6 uiimageviews, say img1 - img6. when i touch and drag img1, it moves. but as i drag the img1 and when it comes near to other uiimageviews, the img1 stops moving and the img which comes near to it, starts moving. this happens when i drag the image very fast and not when i drag the image slowly. And also the dragging is not so smooth...... :(
Here's what i've done so far...
- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
UITouch *touch = [[event allTouches] anyObject];
if (CGRectContainsPoint([self.firstImg frame], [touch locationInView:nil]))
{
[self.view bringSubviewToFront:self.firstImg];
self.firstImg.center = [touch locationInView:nil];
}
else if (CGRectContainsPoint([self.secondImg frame], [touch locationInView:nil]))
{
[self.view bringSubviewToFront:self.secondImg];
self.secondImg.center = [touch locationInView:nil];
}
else if (CGRectContainsPoint([self.thirdImg frame], [touch locationInView:nil]))
{
[self.view bringSubviewToFront:self.thirdImg];
self.thirdImg.center = [touch locationInView:nil];
}
else if (CGRectContainsPoint([self.fourthImg frame], [touch locationInView:nil]))
{
[self.view bringSubviewToFront:self.fourthImg];
self.fourthImg.center = [touch locationInView:nil];
}
else if (CGRectContainsPoint([self.fifthImg frame], [touch locationInView:nil]))
{
[self.view bringSubviewToFront:self.fifthImg];
self.fifthImg.center = [touch locationInView:nil];
}
else if (CGRectContainsPoint([self.sixthImg frame], [touch locationInView:nil]))
{
[self.view bringSubviewToFront:self.sixthImg];
self.sixthImg.center = [touch locationInView:nil];
}
}

Answer 1

There are a number of problems with your implementation:
You're passing nil as the view to locationInView:, which means that if you move the superview or support interface rotation, you will get incorrect coordinates.
You're setting the image view's center to the touch location. Because of this, when the user first touches a view, if the touch isn't exactly centered in the view, the view will jump to be centered at the touch location. This is not the behavior users expect.
You're always checking the views in a fixed order, instead of checking the views from front to back. This is why “when it comes near to other uiimageviews, the img1 stops moving and the img which comes near to it, starts moving.” Your code will always move firstImg if the touch is over firstImg, even if the user was dragging secondImg, because you always check firstImg before checking secondImg.
You're repeating yourself a lot. If you have to write the same thing twice, you should think about factoring it out into a separate function or method. If you have to write the same thing three times (or more), you should almost certainly factor it out.
The simplest answer to all of these problems is to stop using touchesMoved:withEvent: and related methods. Instead, add a UIPanGestureRecognizer to each image view:
- (void)makeImageViewDraggable:(UIImageView *)imageView {
imageView.userInteractionEnabled = YES;
UIPanGestureRecognizer *panner = [[UIPanGestureRecognizer alloc] initWithTarget:self action:#selector(imageViewPannerDidFire:)];
[imageView addGestureRecognizer:panner];
}
- (void)imageViewPannerDidFire:(UIPanGestureRecognizer *)panner {
UIView *view = panner.view;
[view.superview bringSubviewToFront:view];
CGPoint translation = [panner locationInView:view];
CGPoint center = view.center;
center.x += translation.x;
center.y += translation.y;
view.center = center;
[panner setTranslation:CGPointZero inView:view];
}
- (void)viewDidLoad {
[super viewDidLoad];
[self makeImageViewDraggable:self.firstImg];
[self makeImageViewDraggable:self.secondImg];
[self makeImageViewDraggable:self.thirdImg];
[self makeImageViewDraggable:self.fourthImg];
[self makeImageViewDraggable:self.fifthImg];
[self makeImageViewDraggable:self.sixthImg];
}