###导读
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。
####今日头条的拖拽排序界面
####我实现的长按拖拽排序效果
####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cell
MovingCell * 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cell
if ([_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
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