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拖拽排序是新闻类的App可以说是必有的交互设计，如今日头条，网易新闻等。拖拽排序是一个交互体验非常好的设计，简单，方便。
####实现方案
1.给CollectionViewCell添加一个长按手势，通过协议把手势传递到collectionView所在的控制器中。- (void)awakeFromNib{self.layer.cornerRadius = 3;self.layer.masksToBounds = YES;//给每个cell添加一个长按手势UILongPressGestureRecognizer * longPress =[[UILongPressGestureRecognizer alloc]initWithTarget:self action:@selector(longPress:)];longPress.delegate = self;[self addGestureRecognizer:longPress];}
- (void)longPress:(UILongPressGestureRecognizer *)longPress{if (self.delegate && [self.delegate respondsToSelector:@selector(longPress:)]) {[self.delegate longPress:longPress];}
}
2.开始长按时对cell进行截图，并隐藏cell。
- (void)longPress:(UILongPressGestureRecognizer *)longPress{//记录上一次手势的位置static CGPoint startPoint;//触发长按手势的cellMovingCell * cell = (MovingCell *)longPress.view;//开始长按if (longPress.state == UIGestureRecognizerStateBegan) {[self shakeAllCell];//获取cell的截图_snapshotView = [cell snapshotViewAfterScreenUpdates:YES];_snapshotView.center = cell.center;[_collectionView addSubview:_snapshotView];_indexPath= [_collectionView indexPathForCell:cell];_originalCell = cell;_originalCell.hidden = YES;startPoint = [longPress locationInView:_collectionView];}
3、在手势移动的时候，移动截图视图，用遍历的方法求出截图移动到哪个cell的位置，再调用系统的api交换这个cell和隐藏cell的位置，并且数据源中的数据也需要调整顺序
//手势移动的时候else if (longPress.state == UIGestureRecognizerStateChanged){CGFloat tranX = [longPress locationOfTouch:0 inView:_collectionView].x - startPoint.x;CGFloat tranY = [longPress locationOfTouch:0 inView:_collectionView].y - startPoint.y;//设置截图视图位置_snapshotView.center = CGPointApplyAffineTransform(_snapshotView.center, CGAffineTransformMakeTranslation(tranX, tranY));startPoint = [longPress locationOfTouch:0 inView:_collectionView];//计算截图视图和哪个cell相交for (UICollectionViewCell *cell in [_collectionView visibleCells]) {//跳过隐藏的cellif ([_collectionView indexPathForCell:cell] == _indexPath) {continue;}//计算中心距CGFloat space = sqrtf(pow(_snapshotView.center.x - cell.center.x, 2) + powf(_snapshotView.center.y - cell.center.y, 2));//如果相交一半且两个视图Y的绝对值小于高度的一半就移动if (space <= _snapshotView.bounds.size.width * 0.5 && (fabs(_snapshotView.center.y - cell.center.y) <=
_snapshotView.bounds.size.height * 0.5)) {_nextIndexPath = [_collectionView indexPathForCell:cell];if (_nextIndexPath.item > _indexPath.item) {for (NSUInteger i = _indexPath.item; i < _nextIndexPath.item ; i ++) {[self.array exchangeObjectAtIndex:i withObjectAtIndex:i + 1];}}else{for (NSUInteger i = _indexPath.item; i > _nextIndexPath.item ; i --) {[self.array exchangeObjectAtIndex:i withObjectAtIndex:i - 1];}}//移动[_collectionView moveItemAtIndexPath:_indexPath toIndexPath:_nextIndexPath];//设置移动后的起始indexPath_indexPath = _nextIndexPath;break;}}
4.手势停止时，移除截图的view，显示隐藏cell
//手势停止时
}else if(longPress.state == UIGestureRecognizerStateEnded){[self stopShake];[_snapshotView removeFromSuperview];_originalCell.hidden = NO;
}
####其他代码还可以进一步封装，写一个数据管理类dataTool，dataTool作为collectionView的数据源，所有的数据源方法都写到dataTool类中。手势的代理方法也在里面实现，这样控制器会简洁很多，控制器就不需要关注拖拽排序的具体逻辑了。大家有空可以自己写写看，也许你们有更好的处理方案，可以评论交流一下。github地址：https://github.com/HelloYeah/DraggingSort
