UITapGestureRecognizer not responding on animated subview - ios

Question

I have a simple program that creates a subview and animates it across the screen.
As part of this program, I would like to add functionality when the subview is tapped. I am using the following method to create the subview, add the UITapGestureRecognizer and then animate the subview:
int randomName = arc4random() % ([pieceNames count] - 1);
int animationDuration = arc4random() % 5 + 5 ;
NSString *randomPiece = [pieceNames objectAtIndex:randomName];
float yStart = arc4random() % 650;
float yEnd = arc4random() % 650;
UIView *piece = [[PieceView alloc]initWithFrame:CGRectMake(100.0, yStart, 75.0, 75.0)];
[piece setValue:randomPiece forKey:#"name"];
UITapGestureRecognizer *recognizer = [[UITapGestureRecognizer alloc]initWithTarget:self
action:#selector(handleTouch:)];
[piece addGestureRecognizer:recognizer];
[[self view] addSubview:piece];
[UIView animateWithDuration:animationDuration
delay:0.0
options:UIViewAnimationOptionAllowUserInteraction
animations:^(void){
piece.center = CGPointMake(950.0, yEnd);
} completion:^(BOOL done){
[piece removeFromSuperview];
}];
Here is the code that handles the tap:
PieceView *pv = (PieceView *) recognizer.view;
NSLog(#"%# was tapped", pv.name);
What happens is when a PieceView is touched the program does not respond. However, if I remove the animation block then the program responds to the tap.
Why does the UITapGestureRecognizer fail to respond to PieceView when it is animated?

Answer 1

I struggled with this same problem, and it boils down to this: the animated view only ever is in two places: the starting position, and the ending position. Core Animation simply renders the view's layer in interpolated positions between the start and end points over a period of time.
It's almost like when you look to the stars and realize that what you see is not actually what is happening right now. :)
Luckily, the solution is pretty simple. You can put a tap recognizer on the superview and then inspect your animated view's presentationLayer (which does give you an accurate frame at any point in time) to determine if your tap is a hit or not.
I've built a simple UIViewController that demonstrates both the problem and solution:
#import <UIKit/UIKit.h>
#interface MSMViewController : UIViewController
#end
And the implementation:
#import "MSMViewController.h"
#interface MSMViewController ()
#property (nonatomic, strong) UIView *animatedView;
#end
#implementation MSMViewController
- (void)viewDidLoad {
[super viewDidLoad];
CGRect startFrame = CGRectMake(125, 0, 70, 70);
CGRect endFrame = CGRectMake(125, 400, 70, 70);
// draw a box to show where the animated view begins
UIView *startOutlineView = [[UIView alloc] initWithFrame:startFrame];
startOutlineView.layer.borderColor = [UIColor blueColor].CGColor;
startOutlineView.layer.borderWidth = 1;
[self.view addSubview:startOutlineView];
// draw a box to show where the animated view ends
UIView *endOutlineView = [[UIView alloc] initWithFrame:endFrame];
endOutlineView.layer.borderColor = [UIColor blueColor].CGColor;
endOutlineView.layer.borderWidth = 1;
[self.view addSubview:endOutlineView];
self.animatedView = [[UIView alloc] initWithFrame:startFrame];
self.animatedView.backgroundColor = [UIColor yellowColor];
[self.view addSubview:self.animatedView];
[UIView animateWithDuration:10 delay:2 options:UIViewAnimationOptionAllowUserInteraction animations:^{
self.animatedView.frame = endFrame;
} completion:nil];
// this gesture recognizer will only work in the space where endOutlintView is
UITapGestureRecognizer *boxTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(boxTap:)];
[self.animatedView addGestureRecognizer:boxTap];
// this one will work
UITapGestureRecognizer *superviewTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(superviewTap:)];
[self.view addGestureRecognizer:superviewTap];
}
- (void)boxTap:(UITapGestureRecognizer *)tap {
NSLog(#"tap. view is at %#", NSStringFromCGPoint(self.animatedView.frame.origin));
}
- (void)superviewTap:(UITapGestureRecognizer *)tap {
CGRect boxFrame = [self.animatedView.layer.presentationLayer frame];
if (CGRectContainsPoint(boxFrame, [tap locationInView:self.view])) {
NSLog(#"we tapped the box!");
}
}
#end

Answer 2

The solution is much simpler, you just need to set the animation's option UIViewAnimationOptions.allowUserInteraction.
UIView.animate(withDuration: duration, delay: 0.1, options: [.allowUserInteraction], animations: {
...
}, completion: { (completed) in
...
}