从CGaffinetTransform得到旋转

struct CGAffineTransform {
   CGFloat a;
   CGFloat b;
   CGFloat c;
   CGFloat d;
   CGFloat tx;
   CGFloat ty;
};

atan2(rotationTransform.b, rotationTransform.d)

atan2(rotationTransform.b, rotationTransform.a

This duplicate was the basis for my original answer

CGAffineTransformMakeRotation

the source for XAffineTransform here read the API here

final double scaleX = getScaleX0(tr);
final double scaleY = getScaleY0(tr) * flip;
return Math.atan2(tr.getShearY()/scaleY - tr.getShearX()/scaleX,
                  tr.getScaleY()/scaleY + tr.getScaleX()/scaleX);

CGFloat radians = atan2f(self.view.transform.b, self.view.transform.a); 
CGFloat degrees = radians * (180 / M_PI); 

CGFloat angle = [(NSNumber *)[view valueForKeyPath:@"layer.transform.rotation.z"] floatValue];