ios – 确定CALayer已经旋转了多少

我有一个程序,其中CALayer必须旋转到某个值.
如何确定CALayer的当前旋转？
我有一个UIRotationGestureRecognizer来旋转图层：

- (void)handleGesture:(UIGestureRecognizer *)gestureRecognizer
{
    if (gestureRecognizer == rotationGestureRecognizer) {
        NSLog(@"gestureRecRotation: %f",rotationGestureRecognizer.rotation);
        CATransform3D current = _baseLayer.transform;
        _baseLayer.transform = CATransform3DRotate(current,rotationGestureRecognizer.rotation * M_PI / 180,1.0);
    }
}

我从一层必须旋转一定数量的拼图开始.那么如何获得当前图层的旋转？

解决方法

你可以做数学,得到这样的角度：

CATransform3D transform = _baseLayer.transform;
CGFloat angle = atan2(transform.m12,transform.m11);

但是更容易做到如下：

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

从documentation：

Core Animation extends the key-value coding protocol to allow getting and setting of the common values of a layer’s CATransform3D matrix through key paths. Table 4 describes the key paths for which a layer’s transform and sublayerTransform properties are key-value coding and observing compliant