UIView animation with CGAffineTransformMakeScale changes size instantly with decimal number

问题

- (void)startAnimation {
//reverse - shrinking from full size
    if (_reversed == YES) {
        //self.transform = CGAffineTransformMakeScale(1.0, 1.0);
        [UIView animateWithDuration:1.0f delay:0.0f options:UIViewAnimationOptionCurveLinear animations:^{
            self.transform = CGAffineTransformMakeScale(0.1, 0.1); //this line does it instantly
            self.alpha = 0;
        } completion:^(BOOL finished) {
            [self removeFromSuperview];
        }];
    } else {
//non reverse - expanding from middle
        self.transform = CGAffineTransformMakeScale(0.001, 0.001);
        [UIView animateWithDuration:1.0f delay:0.0f options:UIViewAnimationOptionCurveLinear animations:^{
            self.transform = CGAffineTransformMakeScale(1.0, 1.0);
            self.alpha = 0;
        } completion:^(BOOL finished) {
            [self removeFromSuperview];
        }];
    }
}

The non reverse piece of code does work fine as I expect, however when I do the _reversed == YES bit, the transformation inside the animation block happens instantly. If I comment that line of code, then the view stays the right size, but if i uncomment it then it shrinks instantly but the alpha still does the fade animation. Why does this happen?

Edit: I figured out what happened but I don't know how to fix it. The view does do the animation, only the size of the view changes instantly but it still 'slides' into the centre as if it is shrinking (what you see is just a small rectangle sliding to the middle as if it's the top left corner of the object). If I scale the view to 2 first, then scale down to 1 the animation works fine, its only when going from 1 to a decimal number that it doesn't work. Also I used draw rect to create an object with core graphics and the transform problem affects that, but not the actual frame if a set background colour.

回答1:

I was running into a similar issue, where the position of the view would suddenly jump before animating in a change of transform with CGAffineTransformMakeScale. I noticed that the size of the "jump" seemed to be proportional to the scaling that would occur later in the animation.

I could fix this problem by finding that in a viewWillLayoutSubviews() override, I was setting the frame of the view being animated. As a rule, don't set the frames of views that will have a non-identity transform. So in the viewWillLayoutSubviews() override, I set the view's bounds and layer.position instead and now the animation is smooth as silk.

来源：https://stackoverflow.com/questions/20342265/uiview-animation-with-cgaffinetransformmakescale-changes-size-instantly-with-dec