旋转动画

CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
        //默认是顺时针效果，若将fromValue和toValue的值互换，则为逆时针效果
        animation.fromValue = [NSNumber numberWithFloat:0.f];
        animation.toValue = [NSNumber numberWithFloat: M_PI *2];
        animation.duration = 1;
        animation.autoreverses = NO;
        animation.fillMode = kCAFillModeForwards;
        animation.repeatCount = MAXFLOAT; //如果这里想设置成一直自旋转，可以设置为MAXFLOAT，否则设置具体的数值则代表执行多少次
        [_maskBgImg.layer addAnimation:animation forKey:nil];