核心动画setFromValue

Question

我用下面的代码旋转UIImageView：

CABasicAnimation *rotate = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
[rotate setFromValue:[NSNumber numberWithFloat:0.0]];
[rotate setToValue:[NSNumber numberWithFloat:-0.34906585)]];
[rotate setDuration:0.8];
[rotate setTimingFunction:[CAMediaTimingFunction functionWithName: kCAMediaTimingFunctionEaseInEaseOut]];
rotate.removedOnCompletion = NO;
rotate.fillMode = kCAFillModeForwards;
[myUIImageView.layer addAnimation:rotate forKey:@"dangleMyDial"];

但是，每次我调用此函数时，它都会从原始位置开始旋转图像。 我应该使用什么[rotate setFromValue：]; 使它从当前位置旋转？ 有没有显示当前角度的属性？

（0.34906585 Rad等于20Deg）

Answer 1

CATransform3D transform = ((CALayer *) self.myUIImageView.layer.presentationLayer).transform;
CGFloat startAngle = atan2(transform.m12, transform.m11);

CABasicAnimation *rotate = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
[rotate setFromValue:[NSNumber numberWithFloat:startAngle]];
[rotate setByValue:[NSNumber numberWithFloat:-20 * M_PI / 180]];

// ...