ios - 确定 CALayer 旋转了多少

Question

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？我有一个旋转图层的 UIRotationGestureRecognizer:

- (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, 0, 0, 1.0);
    }
}

我从一个必须旋转一定量以适合拼图的图层开始。那么如何获取图层的当前旋转度呢？

Answer 1

你可以这样计算并得到角度:

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

但这样做更容易:

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

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来自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