UICollectionView 自动滚动分页

Question

我的项目有一个 UIcollectionView。这种水平分页有四个对象。我想要我的collectionView自动滚动分页。哪些使用方法？

Answer 1

关于理论，我只是解释一下重点。例如，如果你想在某个地方自动循环显示5张图片，就像广告栏一样。您可以创建一个包含 100 个部分的 UICollectionView，每个部分有 5 个项目。创建UICollectionView后，设置其原始位置等于第50节第0项（MaxSections的中间） ）以便您可以向左或向右滚动。不要担心它会结束，因为当计时器运行时，我已经将位置重置为等于 MaxSections 的中间。不要和我争论：“当用户继续自己滚动时，它也会结束”如果发现只有 5 个图像，他还会继续滚动吗？我相信这个世界上没有几个这么傻的用户！

注意：以下代码中，headerView为UICollectionView，headerNews为data。我建议设置 MaxSections = 100。

在自定义collectionView后添加一个NSTimer（确保首先正确设置UICollectionViewFlowLayout）：

    - (void)addTimer
    {
        NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:3.0f target:self selector:@selector(nextPage) userInfo:nil repeats:YES];
        [[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
        self.timer = timer;

}

然后实现@selector(nextPage):

 - (void)nextPage
{
    // 1.back to the middle of sections
    NSIndexPath *currentIndexPathReset = [self resetIndexPath];

    // 2.next position 
    NSInteger nextItem = currentIndexPathReset.item + 1;
    NSInteger nextSection = currentIndexPathReset.section;
    if (nextItem == self.headerNews.count) {
        nextItem = 0;
        nextSection++;
    }
    NSIndexPath *nextIndexPath = [NSIndexPath indexPathForItem:nextItem inSection:nextSection];

    // 3.scroll to next position
    [self.headerView scrollToItemAtIndexPath:nextIndexPath atScrollPosition:UICollectionViewScrollPositionLeft animated:YES];
}

最后实现resetIndexPath方法：

- (NSIndexPath *)resetIndexPath
{
    // currentIndexPath
    NSIndexPath *currentIndexPath = [[self.headerView indexPathsForVisibleItems] lastObject];
    // back to the middle of sections
    NSIndexPath *currentIndexPathReset = [NSIndexPath indexPathForItem:currentIndexPath.item inSection:MaxSections / 2];
    [self.headerView scrollToItemAtIndexPath:currentIndexPathReset atScrollPosition:UICollectionViewScrollPositionLeft animated:NO];
    return currentIndexPathReset;
}

为了控制 NSTimer ，你必须实现一些其他方法和 UIScrollView 的委托方法：

- (void)removeTimer
{
    // stop NSTimer 
    [self.timer invalidate];
   // clear NSTimer
    self.timer = nil;
}

// UIScrollView' delegate method
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
        [self removeTimer];
}


- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
        [self addTimer];

}

Answer 2

@Elijah_Lam 的 Swift 2.0 版本的回答：

  func addTimer()
  {
    timer = NSTimer.scheduledTimerWithTimeInterval(5.0, target: self, selector: "nextPage", userInfo: nil, repeats: true)
    NSRunLoop.currentRunLoop().addTimer(timer, forMode: NSRunLoopCommonModes)
  }

  func nextPage()
  {
    var ar = cvImg.indexPathsForVisibleItems()

    ///indexPathsForVisibleItems()'s result is not sorted. Sort it by myself...
    ar = ar.sort{if($0.section < $1.section)
      {
      return true
      }
      else if($0.section > $1.section)
    {
      return false
    }
      ///in same section, compare the item
      else if($0.item < $1.item)
      {
        return true
      }
      return false
    }


    var currentIndexPathReset = ar[1]
    if(currentIndexPathReset.section > MaxSections)
    {
      currentIndexPathReset = NSIndexPath(forItem:0, inSection:0)
    }

    cvImg.scrollToItemAtIndexPath(currentIndexPathReset, atScrollPosition: UICollectionViewScrollPosition.Left, animated: true)
  }

  func removeTimer()
  {
    // stop NSTimer
    timer.invalidate()
  }

  // UIScrollView' delegate method
  func scrollViewWillBeginDragging(scrollView: UIScrollView)
  {
    removeTimer()
  }


  func scrollViewDidEndDragging(scrollView: UIScrollView,
    willDecelerate decelerate: Bool)
  {
    addTimer()
  }