How to compute the frame of a UIView before the transform?

问题

Question

I have a UIView and I apply to it a CGAffineTransform. I would like to be able to know the frame of the view if the transform had not be applied.

I am looking for a (simple) solution that handles the case where the transform is the "zero-transform" (which is not invertible).

My attempt

The following does not work for the "zero-transform", I guess.

CGRect result ;

CGAffineTransform transform = self.transform ;

result = CGRectApplyAffineTransform(self.frame, CGAffineTransformInvert(transform)) ;

return result ;

Why?

I need to do this for an animation:

initial settings: I set the transform "to 0". The view is inserted but the frames of all the elements do as if the view was not here.
final settings: I compute the frames of all my elements, and this time I take into account the new view. I set its transform "to 1".

Remarks

My transform is a scale transform.

回答1:

transform does not affect center nor bounds.

So, you can calculate it by this simple code:

    CGPoint center = view.center;
    CGSize size = view.bounds.size;

    CGRect frameForTransformIdentity = CGRectMake(
        center.x - size.width / 2,
        center.y - size.height / 2,
        size.width,
        size.height
    );

回答2:

Swift 4.1 version:

extension UIView
{
    var frameWithoutTransform: CGRect
    {
        let center = self.center
        let size   = self.bounds.size

        return CGRect(x: center.x - size.width  / 2, 
                      y: center.y - size.height / 2,
                  width: size.width,
                 height: size.height)
    }
}

来源：https://stackoverflow.com/questions/26192588/how-to-compute-the-frame-of-a-uiview-before-the-transform

标签

ios

objective-c

uiview

cgaffinetransform

cgsize