前言：
排序思路： 拖拽排序的主要思路是利用在UICollectionView上添加一个长按的手势（UILongPressGestureRecognizer）实现的。 通过监听手势拖拽开始，拖拽中，拖拽结束的事件，然后根据不同的状态做相应的操作。

效果图如下：

UICollectionView拖动排序.PNG

一、在UICollectionView上添加一个长按的手势,并在UICollectionView上面添加一个浮动隐藏的cell,便于拖拽

// 添加长按手势
 UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc]initWithTarget:self action:@selector(longPressRecognizer:)]; 
 longPress.minimumPressDuration = 0.3;
[self.mainView addGestureRecognizer:longPress];
// 添加浮动视图
self.dragingItem = [[WEYuqingChannelCell alloc] initWithFrame:CGRectMake(0, 0, cellWidth, cellWidth/2.0f)]; self.dragingItem.hidden = true;
[self.mainView addSubview:self.dragingItem];

二、拖拽过程的监听

2.1 通过长按操作找到需要被拖动的cell1
2.2 通过拖动cell1找到找到和它交换位置的cell2
2.3 交换cell1和cell2的位置
2.4 替换数据源，把起始位置的数据模型删除，然后将起始位置的数据模型插入到拖拽位置

// 长按手势处理
- (void)longPressRecognizer:(UILongPressGestureRecognizer *)longPress{
    CGPoint point = [longPress locationInView:self.mainView];
    switch (longPress.state) {
        case UIGestureRecognizerStateBegan:{
            [self dragBegin:point];
            NSLog(@"拖拽开始");
            break;
        }
        case UIGestureRecognizerStateChanged:{
            [self dragChanged:point];
            NSLog(@"拖拽中");
            break;
        }
        case UIGestureRecognizerStateEnded: {
            [self dragEnd];
            NSLog(@"拖拽结束");
            [self userSortMontiorCompany];
            break;
        }
        default:{
           break;
        }
    }
}

// 拖拽开始 找到被拖拽的item
- (void)dragBegin:(CGPoint)point{
    self.dragingIndexPath = [self getDragingIndexPathWithPoint:point];
    if (!self.dragingIndexPath) {return;}
    [self.mainView bringSubviewToFront:self.dragingItem];
    WEYuqingChannelCell *item = (WEYuqingChannelCell*)[self.mainView cellForItemAtIndexPath:self.dragingIndexPath];
    item.isMoving = YES;
    // 更新被拖拽的item
    self.dragingItem.hidden = NO;
    self.dragingItem.frame = item.frame;
    self.dragingItem.model = item.model;
    [self.dragingItem setTransform:CGAffineTransformMakeScale(1.1, 1.1)];
}

// 正在被拖拽中
- (void)dragChanged:(CGPoint)point{
    if (!self.dragingIndexPath) {return;}
    self.dragingItem.center = point;
    self.targetIndexPath = [self getTargetIndexPathWithPoint:point];
    // 交换位置 如果没有找到self.targetIndexPath则不交换位置
    if (self.dragingIndexPath && self.targetIndexPath) {
        // 更新数据源
        [self rearrangeInUseTitles];
        //更新item位置
        [self.mainView moveItemAtIndexPath:self.dragingIndexPath toIndexPath:self.targetIndexPath];
        self.dragingIndexPath = self.targetIndexPath;
    }
}

// 拖拽结束
- (void)dragEnd{
    if (!self.dragingIndexPath) {return;}
    CGRect endFrame = [self.mainView cellForItemAtIndexPath:self.dragingIndexPath].frame;
    [self.dragingItem setTransform:CGAffineTransformMakeScale(1.0, 1.0)];
    [UIView animateWithDuration:0.3 animations:^{
        self.dragingItem.frame = endFrame;
    }completion:^(BOOL finished) {
        self.dragingItem.hidden = YES;
        WEYuqingChannelCell *item = (WEYuqingChannelCell*)[self.mainView cellForItemAtIndexPath:self.dragingIndexPath];
        item.isMoving = NO;
    }];
}


// 获取被拖动IndexPath的方法
- (NSIndexPath*)getDragingIndexPathWithPoint:(CGPoint)point{
    NSIndexPath* dragIndexPath = nil;
    //最后剩一个怎不可以排序
    if ([self.mainView numberOfItemsInSection:0] == 1) {return dragIndexPath;}
    for (NSIndexPath *indexPath in self.mainView.indexPathsForVisibleItems) {
        //下半部分不需要排序
        if (indexPath.section > 0) {continue;}
        // 在上半部分中找出相对应的Item
        if (CGRectContainsPoint([self.mainView cellForItemAtIndexPath:indexPath].frame, point)) {
//            if (indexPath.row != 0) {
//                dragIndexPath = indexPath;
//            }
            dragIndexPath = indexPath;
            break;
        }
    }
    return dragIndexPath;
}

// 获取目标IndexPath的方法
- (NSIndexPath*)getTargetIndexPathWithPoint:(CGPoint)point{
    NSIndexPath *targetIndexPath = nil;
    for (NSIndexPath *indexPath in self.mainView.indexPathsForVisibleItems) {
        // 如果是自己不需要排序
        if ([indexPath isEqual:self.dragingIndexPath]) {continue;}
        //第二组不需要排序
        if (indexPath.section > 0) {continue;}
        //在第一组中找出将被替换位置的Item
        if (CGRectContainsPoint([self.mainView cellForItemAtIndexPath:indexPath].frame, point)) {
//            if (indexPath.row != 0) {
//                targetIndexPath = indexPath;
//            }
             targetIndexPath = indexPath;
        }
    }
    return targetIndexPath;
}


//拖拽排序后需要重新排序数据源
- (void)rearrangeInUseTitles {
    WEYuqingChannelModel *model = [self.dataArray objectAtIndex:self.dragingIndexPath.row];
    [self.dataArray removeObject:model];
    [self.dataArray insertObject:model atIndex:self.targetIndexPath.row];
}

三、UI处理完毕，调用数据排序接口就可以了

#pragma mark - 频道排序
- (void)userSortMontiorCompany {
    NSMutableArray *idArr = @[].mutableCopy;
    for (WEYuqingChannelModel *model in self.dataArray) {
        [idArr addObject:model.ID];
    }
    NSString *idStr = [idArr componentsJoinedByString:@","];
    [WEHttpRequest requestWithConfig:^(WEUrlRequestConfig * _Nonnull request) {
        request.methodType = WEHttpMethodPOST;
        request.baseUrl = HostUrl;
        request.url = @"docinfo/channel/sort";
        request.parameters = @{@"cnId":idStr};
        request.availableType = WERequestAvailableTypeLoged;
        [request setValue:[WELoginManager sharedInstance].accessToken forHeaderField:kAccessToken];
    } success:^(NSDictionary * _Nullable responseObject) {
         NSLog(@"打印日志。%@",responseObject);
        [[NSNotificationCenter defaultCenter] postNotificationName:@"channelStatusChanged" object:nil];
    } failed:^(NSError * _Nullable error) {
    }];
}