How to rotate a view in place after transform as been applied?

0
votes

I'm using a variant of this code to slighty rotate a UIButton about its center:

CGFloat jiggleAngle = (-M_PI * 2.0) * (1.0 / 64.0);
self.transform = CGAffineTransformRotate(self.transform, jiggleAngle);

This code generally works as expected and rotates the button in-place, about 12 degrees counter-clockwise. However, this only works if I do not reposition the button inside my layoutSubviews method. If I do any repositioning of the button at all from its initially laid-out location, the attempt to rotate above results in the button's disappearance. If the angle I choose for rotation is an exact multiple of 90 degrees, the rotation works somehow even after a move in layoutSubviews.

I understand that my button's transform is being altered in layoutSubviews and this results in the subsequent weirdness when I attempt to rotate it with the above code. I have currently worked around this problem by placing the button I wish to rotate inside another UIView and then moving that view around as desired, but I'd like a better solution that doesn't require redoing my screen layouts.

How can I adjust/alter my button's transform after a move, so that this rotation code continues to work as expected?

1
iosobjective-c

1 Answers

1
votes

The problem you are facing is that a view's frame is "undefined" if it's transform isn't the identity transform.

What you should do is use the view's center property to move it around. That works even if you've changed it's transform.

You can also apply a rotation to the view's layer instead of the view (although be aware that the layer transform is a CATransform3D, a 4x4 transformation matrix instead of a 3x3, so you need different methods to manipulate it.)