iOS 实现淡入淡出加滚动轮播动画

设计稿在此  

思路：持有两个view,一个是当前展示的，一个是将要展示的，当前展示的执行透明度动画和

位移动画，执行结束之后，将要展示的视图执行透明度动画和位移动画，

其中透明度动画是先执行的

计时器执行的核心代码，是位移动画和透明度动画的组合

- (void)fadeTimeHandler
{
    if (self.isAnimating) {
        return;
    }
    
    float w = self.frame.size.width;
    float h = self.frame.size.height;
    
    self.isAnimating = YES;
    [self.reuseCells removeObject:_currentCell];
    [self.reuseCells removeObject:_willShowCell];
    @weakify(self);
    [UIView animateWithDuration:0.4 animations:^{
        @strongify(self);
        self.currentCell.alpha = 0;
    }
                     completion:^(BOOL finished) {
    }];
    [UIView animateWithDuration:0.3 delay:0.1 options:UIViewAnimationOptionCurveLinear animations:^{
        self.currentCell.frame = CGRectMake(0, -4, w, h);
    } completion:^(BOOL finished) {
        [self showNext];
        self.currentCell.frame = CGRectMake(0, 0, w, h);
    }];
}

- (void)showNext
{
    [UIView animateWithDuration:0.4 animations:^{
        self.willShowCell.alpha = 1;
    } completion:^(BOOL finished) {
    }] ;
    float w = self.frame.size.width;
    float h = self.frame.size.height;
    
    [UIView animateWithDuration:0.3 delay:0.1 options:UIViewAnimationOptionCurveLinear animations:^{
        self.willShowCell.frame = CGRectMake(0, 0, w, h);
    } completion:^(BOOL finished) {
        self->_currentIndex++;
        int count = (int)[self.dataSource numberOfRowsForRollingNoticeView:self];
        if (self->_currentIndex > count - 1) {
            self->_currentIndex = 0;
        }
        if (self.currentCell && self.willShowCell) {
            [self.reuseCells addObject:self.currentCell];
        }
        self.isAnimating = NO;
        int willShowIndex = self->_currentIndex + 1;
        if (willShowIndex > count - 1) {
            willShowIndex = 0;
        }
        self->_currentCell = self->_willShowCell;
        self->_willShowCell = [self.dataSource rollingNoticeView:self cellAtIndex:willShowIndex];
        self->_willShowCell.frame = CGRectMake(0, 4, w, h);
        self->_willShowCell.alpha = 0;
        [self addSubview:self.willShowCell];
    }];
}

demo