UITableView：如何禁用将项目拖动到特定行？

Question

我有一个带有可拖动行的UITableView，我可以添加/删除项目。数据源是NSMutableArray。

现在，如果我使用“添加新功能”移动该行，则应用程序崩溃，因为dataSource较小，因为尚未添加此行。

所以我修改了这段代码：

- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath {
        if (indexPath.row >= [dataList count]) return NO;
        return YES;
    }

现在我不能再动了。但是，我仍然可以在这样的行之后移动其他行，因此代码崩溃。

我该如何解决这个问题？有没有办法禁用拖动“到”特定行，而不仅仅是从？

感谢

Answer 1

这正是UITableViewDelegate方法

-tableView:targetIndexPathForMoveFromRowAtIndexPath:toProposedIndexPath:

是为了。它会适合你的目的吗？ Here's文档。

Answer 2

之前的答案和文档（请参阅其他答案中提到的this和this）有用但不完整。我需要：

• 实施例
• 知道如果建议的行动不合适该怎么办

不用多说，这里有一些

实施例

接受所有动作

- (NSIndexPath *)tableView:(UITableView *)tableView
    targetIndexPathForMoveFromRowAtIndexPath:(NSIndexPath *)sourceIndexPath
                         toProposedIndexPath:(NSIndexPath *)proposedDestinationIndexPath
{
    return proposedDestinationIndexPath;
}

拒绝所有移动，将行返回到其初始位置

- (NSIndexPath *)tableView:(UITableView *)tableView
    targetIndexPathForMoveFromRowAtIndexPath:(NSIndexPath *)sourceIndexPath
                         toProposedIndexPath:(NSIndexPath *)proposedDestinationIndexPath
{
    return sourceIndexPath;
}

拒绝一些移动，将任何被拒绝的行返回到其初始位置

- (NSIndexPath *)tableView:(UITableView *)tableView
    targetIndexPathForMoveFromRowAtIndexPath:(NSIndexPath *)sourceIndexPath
                         toProposedIndexPath:(NSIndexPath *)proposedDestinationIndexPath
{
    if (... some condition ...) {
        return sourceIndexPath;
    }
    return proposedDestinationIndexPath;
}

Answer 3

如何修改最后一行：

- (NSIndexPath *)tableView:(UITableView *)tableView
targetIndexPathForMoveFromRowAtIndexPath:(NSIndexPath *)sourceIndexPath
       toProposedIndexPath:(NSIndexPath *)proposedDestinationIndexPath
{
    // get number of objects
    NSUInteger numberOfObjects = [[[BNRItemStore sharedStore] allItems] count]; 

    if ( (proposedDestinationIndexPath.row+1==numberOfObjects) || (sourceIndexPath.row+1==numberOfObjects) ) {
        NSLog(@"HERE");
        return sourceIndexPath;
    }
    else{
         NSLog(@"count=%d %d", [[[BNRItemStore sharedStore] allItems] count], proposedDestinationIndexPath.row);
        return proposedDestinationIndexPath;
    }
}

Answer 4

Following is the example to restrict drag and drop to 0th index of 1st section UICollectionView
It worked for me :)

func collectionView(_ collectionView: UICollectionView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?) -> UICollectionViewDropProposal {

        if session.localDragSession != nil
        {
#//restricts dropping to 0th index
            if destinationIndexPath?.row == 0{
               return UICollectionViewDropProposal(operation: .forbidden) 
            }

            if collectionView.hasActiveDrag
            {
                return UICollectionViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath)
            }
            else
            {
                return UICollectionViewDropProposal(operation: .copy, intent: .insertAtDestinationIndexPath)
            }
        }

    }

    func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
#//prevents dragging item from 0th index
        if indexPath.row == 0{
            return [UIDragItem]() //prevents dragging item from 0th index
        }

        let item = self.yourArray[indexPath.row]
        let itemProvider = NSItemProvider(object: item)
        let dragItem = UIDragItem(itemProvider: itemProvider)
        dragItem.localObject = item
        return [dragItem]
    }