UICollectionView的item的长按移动

点击每一个item后移动item改变item的位置。
实现这个功能有两种方案
1.第一种使用苹果给出的API直接调方法（IOS9以后）
2.第二种就是自己苦b的写移动前后的逻辑
通过查资料获得的两个方法代码大致如下

第一种直接调API

增加长按手势

//此处给其增加长按手势，用此手势触发cell移动效果
    UILongPressGestureRecognizer *longGesture = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(handlelongGesture:)];
    [_itemCollectionVIew addGestureRecognizer:longGesture];

手势调用的方法

//ios9以后的系统（ios9API）
-(void)IOS9_action:(UILongPressGestureRecognizer *)longGesture{
    //判断手势状态
    switch (longGesture.state) {
        case UIGestureRecognizerStateBegan:{
//增加的抖动的动画
            [self shake];
            //判断手势落点位置是否在路径上
            NSIndexPath *indexPath = [self.itemCollectionVIew indexPathForItemAtPoint:[longGesture locationInView:self.itemCollectionVIew]];
            if (indexPath == nil) {
                break;
            }
            //在路径上则开始移动该路径上的cell
            [self.itemCollectionVIew beginInteractiveMovementForItemAtIndexPath:indexPath];
        }
            break;
        case UIGestureRecognizerStateChanged:
            //移动过程当中随时更新cell位置
            [self.itemCollectionVIew updateInteractiveMovementTargetPosition:[longGesture locationInView:self.itemCollectionVIew]];
            break;
        case UIGestureRecognizerStateEnded:
            //移动结束后关闭cell移动
            [self.itemCollectionVIew endInteractiveMovement];
            break;
        default:
            [self.itemCollectionVIew cancelInteractiveMovement];
            break;
    }
}

系统的回调方法

//是否允许移动item（ios9API）
- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath{
    //返回YES允许其item移动
    return YES;
}
//item移动后改变的item的回调（ios9API）
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath*)destinationIndexPath {
//此处可以设置移动后的数据源的数组中的位置
//也可以不写，只是刷新后cell的状态不是你所想要的
}

调换数据源数组中的位置，可以参考下面方法
//self.dataArray是数据源数组
//SelectedListModel是cell的model
//将数据源数组按照改变的item的位置重新组装数组

-(void)compareMoveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath*)destinationIndexPath{
    NSInteger location = 0;
    NSInteger length = 0;
    if (sourceIndexPath.item > destinationIndexPath.item) {
        location = destinationIndexPath.item;
    }else{
        location = sourceIndexPath.item;
    }
    length = ABS(destinationIndexPath.item - sourceIndexPath.item)+1;
    NSRange rang = NSMakeRange(location , length);
    NSMutableIndexSet *set = [NSMutableIndexSet indexSet];
    [set addIndexesInRange:rang];
    NSMutableArray *array = [NSMutableArray arrayWithArray:[self.dataArray subarrayWithRange:rang]];
    [self.dataArray removeObjectsAtIndexes:set];
    if (location == sourceIndexPath.item) {
        SelectedListModel *model1 = array.firstObject;
        [array removeObjectAtIndex:0];
        [array addObject:model1];
        
    }else{
        SelectedListModel *model1 = array.lastObject;
        [array removeLastObject];
        [array insertObject:model1 atIndex:0];
    }
    [self.dataArray insertObjects:array atIndexes:set];
}

第二种是为了适配iOS9以前的系统

用到的属性

/**之前选中cell的NSIndexPath*/
@property (nonatomic, strong) NSIndexPath *oldIndexPath;
/**单元格的截图*/
@property (nonatomic, strong) UIView *snapshotView;
/**之前选中cell的NSIndexPath*/
@property (nonatomic, strong) NSIndexPath *moveIndexPath;

手势实现的方法

//ios9以前的系统
-(void)action:(UILongPressGestureRecognizer *)longPress{
    switch (longPress.state) {
        case UIGestureRecognizerStateBegan:
        { // 手势开始
            //判断手势落点位置是否在row上
            NSIndexPath *indexPath = [self.itemCollectionVIew indexPathForItemAtPoint:[longPress locationInView:self.itemCollectionVIew]];
            self.oldIndexPath = indexPath;
            if (indexPath == nil) {
                break;
            }
            UICollectionViewCell *cell = [self.itemCollectionVIew cellForItemAtIndexPath:indexPath];
            // 使用系统的截图功能,得到cell的截图视图
            UIView *snapshotView = [cell snapshotViewAfterScreenUpdates:NO];
            snapshotView.layer.cornerRadius = 3;
            snapshotView.layer.masksToBounds = YES;
            snapshotView.frame = cell.frame;
            [self.itemCollectionVIew addSubview:self.snapshotView = snapshotView];
            // 截图后隐藏当前cell
            cell.hidden = YES;
            
            CGPoint currentPoint = [longPress locationInView:self.itemCollectionVIew];
            [UIView animateWithDuration:0.25 animations:^{
                snapshotView.transform = CGAffineTransformMakeScale(1.05, 1.05);
                snapshotView.center = currentPoint;
            }];
        }
            break;
        case UIGestureRecognizerStateChanged:
        { // 手势改变
            //当前手指位置 截图视图位置随着手指移动而移动
            CGPoint currentPoint = [longPress locationInView:self.itemCollectionVIew];
            self.snapshotView.center = currentPoint;
            // 计算截图视图和哪个可见cell相交
            for (UICollectionViewCell *cell in self.itemCollectionVIew.visibleCells) {
                // 当前隐藏的cell就不需要交换了,直接continue
                if ([self.itemCollectionVIew indexPathForCell:cell] == self.oldIndexPath) {
                    continue;
                }
                // 计算中心距
                CGFloat space = sqrtf(pow(self.snapshotView.center.x - cell.center.x, 2) + powf(self.snapshotView.center.y - cell.center.y, 2));
                if (space <= self.snapshotView.bounds.size.width / 2) {
                    self.moveIndexPath = [self.itemCollectionVIew indexPathForCell:cell];
                    //移动 会调用willMoveToIndexPath方法更新数据源
                    [self.itemCollectionVIew moveItemAtIndexPath:self.oldIndexPath toIndexPath:self.moveIndexPath];
//上面提到的方法，将数据源数组按照改变的item的位置重新组装数组
                    [self compareMoveItemAtIndexPath:_oldIndexPath toIndexPath:_moveIndexPath];
                    //设置移动后的起始indexPath
                    self.oldIndexPath = self.moveIndexPath;
                    break;
                }
            }
        }
            break;
        default:
        { // 手势结束和其他状态
            UICollectionViewCell *cell = [self.itemCollectionVIew cellForItemAtIndexPath:self.oldIndexPath];
            // 结束动画过程中停止交互,防止出问题
            self.itemCollectionVIew.userInteractionEnabled = NO;
            // 给截图视图一个动画移动到隐藏cell的新位置
            [UIView animateWithDuration:0.25 animations:^{
                self.snapshotView.center = cell.center;
                self.snapshotView.transform = CGAffineTransformMakeScale(1.0, 1.0);
            } completion:^(BOOL finished) {
                // 移除截图视图,显示隐藏的cell并开始交互
                [self.snapshotView removeFromSuperview];
                cell.hidden = NO;
                self.itemCollectionVIew.userInteractionEnabled = YES;
            }];
        }
            break;
    }
}

根据需要调用

- (void)handlelongGesture:(UILongPressGestureRecognizer *)longGesture {
    //判断是否是ios以前的系统
    if ([[[UIDevice currentDevice] systemVersion] floatValue] < 9.0){
        [self action:longGesture];
    }else{
       [self IOS9_action:longGesture];
    }
}

注释写的很清楚，理解应该不是很难。。。