CALayer未在设备上显示

Question

我有一个自定义图层（它是CALayer的子类）。在该课程中，我重写方法needsDisplayForKey:，initWithLayer:，actionForKey:，如下所示：

-(id<CAAction>)actionForKey:(NSString *)event 
{
    if ([event isEqualToString:@"duration"]) {
        return [self animationForKey:event];
    }  
    return [super actionForKey:event];
}

- (CABasicAnimation *)animationForKey:(NSString *)key
{
    NSString *animValue = [[self presentationLayer] valueForKey:key];
    CABasicAnimation *anim;

    if([key isEqualToString:@"duration"]) {
        anim = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
        anim.repeatCount = HUGE_VAL;
        anim.autoreverses = YES;
        anim.fromValue = [NSNumber numberWithFloat:0.5f];       
    }
    anim.duration = 2;    
    return anim;
}

我使用此CALayer如下

@property(strong,nonatomic)ArcLayer *arcLayer;

self.arcLayer=[ArcLayer layer];;
self.arcLayer.duration=2;
self.arcLayer.frame = self.bounds;
self.arcLayer.backgroundColor = [UIColor greenColor].CGColor;
[self.layer addSublayer:self.arcLayer];

此代码在模拟器上正常工作，在模拟器上显示带动画的ArcLayer。但是，ArcLayer未显示在设备上。

为什么它不能在设备上运行？