如何让视图永远旋转？

Question

是否有一种方法可以让视图以指定的速度永久旋转？对于指标性的东西，我需要它。我知道有一个古怪的Lxxxxx00ff常数（记不清了）代表“永远”。

Answer 1

您可以将HUGE_VAL用于浮点值（如果我没记错的话，动画的repeatCount属性是一个浮点数）。

要设置动画，您可以使用+animationWithKeyPath:方法创建CAAnimation对象：

CABasicAnimation* animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
animation.fromValue = [NSNumber numberWithFloat:0.0f];
animation.toValue = [NSNumber numberWithFloat: 2*M_PI];
animation.duration = 3.0f;
animation.repeatCount = HUGE_VAL;
[rotView.layer addAnimation:animation forKey:@"MyAnimation"];

如果我记得正确使用UIView动画创建这种旋转是不可能的，因为360度旋转（2 * M_PI弧度）已优化为完全不旋转。

---

编辑：添加了Swift版本。

    let animation = CABasicAnimation(keyPath: "transform.rotation.z")
    animation.fromValue = NSNumber(value: 0.0)
    animation.toValue = NSNumber(value: 2*Double.pi)
    animation.duration = 3.0
    animation.repeatCount = Float.greatestFiniteMagnitude
    rotView.layer.add(animation, forKey: "MyAnimation")

Answer 2

我对此的解决方案有点笨拙，因为它不使用核心动画，但至少可以真正地实现[[forever，并且不需要您设置多个动画步骤。

...
// runs at 25 fps
NSTimer* timer = [NSTimer scheduledTimerWithTimeInterval:1.0/25
                          target:self
                          selector:@selector(rotate)
                          userInfo:nil
                          repeats:YES];
[timer fire];
...

- (void)rotate {
    static int rotation = 0;

    // assuming one whole rotation per second
    rotation += 360.0 / 25.0;
    if (rotation > 360.0) {
        rotation -= 360.0;
    }
    animatedView.transform = CGAffineTransformMakeRotation(rotation * M_PI / 180.0);
}

Answer 3

我的赌注是：

-(void)animationDidStopSelector:... {
  [UIView beginAnimations:nil context:NULL];
  // you can change next 2 settings to setAnimationRepeatCount and set it to CGFLOAT_MAX
  [UIView setAnimationDelegate:self];
  [UIView setAnimationDidStopSelector:@selector(animationDidStopSelector:...)];
  [UIView setAnimationDuration:...

  [view setTransform: CGAffineTransformRotate(CGAffineTransformIdentity, 6.28318531)];

  [UIView commitAnimations];
}

//start rotation
[self animationDidStopSelector:...];

更好的选择：
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationRepeatCount: CGFLOAT_MAX];
[UIView setAnimationDuration:2.0f];

[view setTransform: CGAffineTransformMakeRotation(6.28318531)];

[UIView commitAnimations];