创建动画以使UIImageView无限向上和向下（几乎浮动）时，如何在动画结束时停止暂停？

Question

Here's the code I'm using to take a UIImageView and make it float up and down.

    [UIView animateKeyframesWithDuration:2.0 delay:0.0 options:UIViewKeyframeAnimationOptionRepeat animations:^{
        [UIView addKeyframeWithRelativeStartTime:0.0 relativeDuration:0.25 animations:^{
            self.slider.transform = CGAffineTransformMakeTranslation(0, -5.0);
        }];
        [UIView addKeyframeWithRelativeStartTime:0.25 relativeDuration:0.5 animations:^{
            self.slider.transform = CGAffineTransformMakeTranslation(0, 5.0);
        }];
        [UIView addKeyframeWithRelativeStartTime:0.75 relativeDuration:0.25 animations:^{
            self.slider.transform = CGAffineTransformMakeTranslation(0, 0.0);
        }];
    } completion:^(BOOL finished) {

    }];

However, it comes out looking like this with this delay after the animation ends and before it restarts.

How do I make it fluid?

Answer 1

I'm not sure what effect you're going for exactly, but I think this gives you something like your code does without the delay. I usually do this by animating a constraint, rather than using transforms. In this example, I've made an IBOutlet (topCon) to the constraint to the top of the view:

-(IBAction)floatView:(id)sender {
    static int i= 1;
    static float duration = .25;
    [UIView animateWithDuration:duration delay:0 options:UIViewAnimationOptionCurveLinear animations:^{
        self.topCon.constant = self.topCon.constant - (5 * i);
        [self.view layoutIfNeeded];
    } completion:^(BOOL finished) {
        i = (i == 1 || i == 2)? -2 : 2;
        duration = 0.5;
        [self floatView:self];
    }];
}