当应用程序进入和退出后台时暂停和恢复核心动画

Question

我有一个简单的 CABasicAnimation 连接为无限动画（我有一个永远旋转的轮子）。这是我设置显式动画的方法：

-(void)perform360rotation:(UIImageView*) imageView {
CABasicAnimation* anim = [CABasicAnimation animationWithKeyPath:@"transform.rotation"];
// to rotate around a specific axis, specify it in the KeyPath parameter like below
//CABasicAnimation* anim = [CABasicAnimation animationWithKeyPath:@"transform.rotation.x"];
[anim setDuration:self.speed]; // Animation duration 
[anim setAutoreverses:NO];
[anim setRepeatCount:HUGE_VALF]; // Perfrom animation large number of times
[anim setFromValue:[NSNumber numberWithDouble:0.0f]];
[anim setToValue:[NSNumber numberWithDouble:(M_PI * 2.0f)]];
[[imageView layer] addAnimation:anim forKey:@"wheeloRotation"];
}

我从 viewWillAppear 方法调用此动画方法。当应用程序进入后台然后重新出现时，动画不再起作用。 经过谷歌搜索，我从苹果公司找到了这个。一切都很好，我在同一个 viewcontroller.m 文件中实现了 Apple 的建议，该文件具有用于旋转视图的 Perform360rotation 方法。

-(void)pauseLayer:(CALayer*)layer
{
CFTimeInterval pausedTime = [layer convertTime:CACurrentMediaTime() fromLayer:[self.wheelView layer]];
layer.speed = 0.0;
layer.timeOffset = pausedTime;
NSLog(@"pauseLayer:paused time = %f",pausedTime);
}

-(void)resumeLayer:(CALayer*)layer
{
CFTimeInterval pausedTime = [layer timeOffset];
NSLog(@"resumeLayer:paused time = %f",pausedTime);
layer.speed = 1.0;
layer.timeOffset = 0.0;
layer.beginTime = 0.0;
CFTimeInterval timeSincePause = [layer convertTime:CACurrentMediaTime() fromLayer:[self.wheelView layer]] - pausedTime;
layer.beginTime = timeSincePause;
}

再次在谷歌上搜索，我看到普遍的共识是我从 AppDelegate 调用暂停和恢复方法。所以我这样做了（lVC是我在这个问题开始时提到的viewcontroller.m类。pauseLayer和resumeLayer方法是从其viewWillAppear和viewWillDisappear方法内部调用的）：

- (void)applicationDidEnterBackground:(UIApplication *)application
{
[lVC viewWillDisappear:YES];
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
[lVC viewWillAppear:YES];

}

还没有骰子。当应用程序重新进入前台时，动画仍然不会恢复。我做错了什么吗？

Answer 1

调用 viewWillAppear 可能会导致其他副作用，并且通常不是开始动画的好地方，请尝试监听 UIApplicationWillEnterForegroundNotification 并在处理程序。