iOS：我想不断旋转图像，但是不起作用

Question

具有关于stackoverflow的几个示例的代码。但是我的图像没有旋转..知道为什么吗？它显示在屏幕上，但是固定的。.

-(UIImageView *)movablePropeller
{
    if(!_movablePropeller){
        _movablePropeller = [[UIImageView alloc] initWithFrame:self.frame];
        _movablePropeller.image = [UIImage imageNamed:@"MovablePropeller"];
        [self addSubview:_movablePropeller];
    }
    return _movablePropeller;
}

- (void)startPropeller
{
    CABasicAnimation *rotation;
    rotation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
    rotation.fromValue = [NSNumber numberWithFloat:0.0f];
    rotation.toValue = [NSNumber numberWithFloat:(2 * M_PI)];
    rotation.cumulative = true;
    rotation.duration = 0.7f; // Speed
    rotation.repeatCount = INFINITY; // Repeat forever. Can be a finite number.

    [self.movablePropeller.layer removeAllAnimations];
    [self.movablePropeller.layer addAnimation:rotation forKey:@"Spin"];
}

（当然，我很乐意将其放在单独的线程中，而不是阻塞UI）