当应用程序进入和退出背景时暂停和恢复核心动画

Question

我有一个简单的CABasicAnimation作为一个无限动画（我有一个轮子，我永远不停地旋转）连线起来。这里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"]; 
} 

我从我的viewWillAppear方法调用这个animtion方法。当应用程序进入后台并重新显示时，动画不再起作用。当谷歌搜索时，我想出了苹果公司的this。一切都好，我在相同的viewcontroller.m文件中实现了Apple的这样的推荐，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; 
} 

同样，在谷歌上搜索，我看到的普遍共识是，我所说的暂停和恢复从AppDelegate的方法。所以，我没有他们这样的（LVC是有我在这个问题开始提到的viewcontroller.m类pauseLayer和resumeLayer方法正在从viewWillAppear中和viewWillDisappear方法中调用。）：

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

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

} 

无骰子呢。当应用重新输入前景时，动画仍然不会恢复。有什么我做错了吗？

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，请尝试听取UIApplicationWillEnterForegroundNotification并在处理程序中添加您的resumeLayer:。