iOS UICollectionViewCell 的拖动

1.长按cell的情况下实现拖动，所以理应想到用长按手势。

2.既然实现移动cell，就要看看UICollectionView 有没有方法或者协议可以移动的。通过查看UICollectionView的协议方法，可以在UICollectionViewDataSource中看到有两个方法。

- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath*)destinationIndexPath;

 3.OK 知道了以上两个步骤，那么就可以开始写代码了。

// 设置手势
- (void)setupGesture
{
    UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(handlelongGesture:)];
    
    [self.collectionView addGestureRecognizer:longPress];
}
- (void)handlelongGesture:(UILongPressGestureRecognizer *)longGesture {
    //判断手势状态
    switch (longGesture.state) {
        case UIGestureRecognizerStateBegan:
　　　　{
            //判断手势落点位置是否在路径上
            NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:[longGesture locationInView:self.collectionView]];
            if (indexPath == nil) {
                break;
            }
            //在路径上则开始移动该路径上的cell
            [self.collectionView beginInteractiveMovementForItemAtIndexPath:indexPath];
        }
            break;
        case UIGestureRecognizerStateChanged:
            //移动过程当中随时更新cell位置
            [self.collectionView updateInteractiveMovementTargetPosition:[longGesture locationInView:self.collectionView]];
            break;
        case UIGestureRecognizerStateEnded:
            //移动结束后关闭cell移动
            [self.collectionView endInteractiveMovement];
            break;
        default:
            [self.collectionView cancelInteractiveMovement];
            break;
    }
}
- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath{
    //返回YES允许其item移动
    return YES;
}
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath*)destinationIndexPath {
    //取出源item数据
    id objc = [_dataSource objectAtIndex:sourceIndexPath.item];
    //从资源数组中移除该数据
    [_dataSource removeObject:objc];
    //将数据插入到资源数组中的目标位置上
    [_dataSource insertObject:objc atIndex:destinationIndexPath.item];
}

注：_dataSource 是你的数据源。