Update view's frame while it's being anima

Question

I'm doing an animation like this:

CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    animation.duration = 100.0;
    animation.path = self.animationPath.CGPath;
    [view.layer addAnimation:animation forKey:@"animation"];

Works fine, however, this now fails when trying to detect touches on the object that is moving around the screen:

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event
{
    for (UIView* subview in self.subviews ) {
        if ( [subview hitTest:[self convertPoint:point toView:subview] withEvent:event] != nil ) {
            [self handleTap];
            return YES;
        }
    }
    return NO;
}

It fails because the view's frame is no longer the same as it's apparent position on the screen when it is being animated. How can I get pointInside to work with a view that is being animated?

Answer 1

Short answer: You can't. In both UIView and Core Animation animations, the view/layer does not actually move as it's position appears to be animating. Instead, there is a "presentation layer" that draws the animated object as it moves.

If you want to make objects tappable while a position animation is "in flight" you have to put a tap gesture recognizer on a superview that spans the entire area the view will travel over, and then do hit testing on the presentation layer of the object that's being animated.

Edit:

I have a project on Github called iOS CAAnimation Group demo that is a working demonstration of how to use hit testing on the presentation layer to detect taps on a view that's being animated along a complex path.

The code is written in Objective-C, but it should still be an illustration of the concept and techniques. Let me know if you have trouble making sense of the Objective-C code. I'm decent at Swift, although I'm still paying the bills in mostly Objective-C, so that's the syntax I know best.

Answer 2

This is my code to do this

#import "ViewController.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet AnimatableView *animableView;
@end

@implementation ViewController

- (void)animateAlongPath
{
    UIBezierPath * path = [UIBezierPath bezierPathWithRect:self.view.frame];

    CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    animation.duration = 10;
    animation.path = path.CGPath;
    animation.removedOnCompletion = NO;
    animation.fillMode = @"kCAFillModeForwards";
    [self.animableView.layer addAnimation:animation forKey:@"animation"];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (IBAction)animate:(id)sender {
    [self animateAlongPath];
}

-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView: [touch view]];

    CALayer * selectedlayer = (CALayer*)[self.animableView.layer.presentationLayer hitTest:location];
    if(selectedlayer != nil)
        NSLog(@"touched");
    else
        NSLog(@"dont touched");
}


@end

I hope this helps you