需求是 app 首页 banner 图

1,循环滑动

2,左右翻页

3,自动滑动

原理:

用的是一个 UICollectionView 实现

1,把数据源扩大 (2倍 + 1) 

- (NSInteger)collectionView:(UICollectionView*)collectionView numberOfItemsInSection:(NSInteger)section

{

    // self.datas.count * 2      防止 第一个往左轮播时数组越界

    // self.datas.count * 2 + 1  防止 最后一个往右轮播时数组越界

    return self.datas.count * 2 + 1;

}

2,将要停止拖拽时

- (void)scrollViewWillEndDragging:(UIScrollView*)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inoutCGPoint*)targetContentOffset

{

    CGPoint target = [self nearestTargetOffsetForOffset:*targetContentOffset];

    targetContentOffset->x= target.x;

    targetContentOffset->y= target.y;

}

- (CGPoint)nearestTargetOffsetForOffset:(CGPoint)offset

{

    CGFloat pageSize = self.collectionView.frame.size.width;

    CGFloatpreFixSize = pageSize - (CGRectGetWidth(self.collectionView.frame) - pageSize) /2;

    NSIntegerpage  =round((offset.x- preFixSize)/ pageSize);

    CGFloattargetX = page * pageSize;

    returnCGPointMake(targetX + preFixSize, offset.y);

}

3,停止拖拽时和停止动画时 

- (void)scrollViewDidEndScrollingAnimation:(UIScrollView*)scrollView

{

    [self scrollToNextDone];

}

- (void)scrollViewDidEndDecelerating:(UIScrollView*)scrollView

{

    [self scrollToNextDone];

}

- (void)scrollToNextDone

{

    [self stopTimer];

    [self startTimer];

    CGPoint center = CGPointMake(self.collectionView.contentOffset.x + self.collectionView.center.x, self.collectionView.center.y);

    NSIndexPath *nowIndexPath = [self.collectionView indexPathForItemAtPoint:center];

    if(nowIndexPath &&self.datas.count!=0) {

        NSIndexPath *nextIndexPath = [NSIndexPath indexPathForItem:(nowIndexPath.item % self.datas.count + self.datas.count) inSection:0];

// 取 self.datas.count + (1~~~ self.datas.count-1)

        [self.collectionView scrollToItemAtIndexPath:nextIndexPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];

    }

}

源代码地址:

https://github.com/miantiao77/LXCyCleProject.git