objective-c - 使用拖放重新排列时，小圆线栏卡在 NSOutlineView 顶部

Question

我有 NSOutlineView ，目前只列出根项的子项。一切正常，除非我尝试使用拖放重新排列项目。前面有圆圈的线始终位于顶行上方，并且在需要在其他项目之间拖动时不会跟随我的项目。但是，我仍然可以正确地获取索引位置，因此我仍然可以在数据源中正确地重新排列它们。我不想通过将它们拖到彼此上来重新排列项目，我只想重新排列根级别的项目（如 Mac 上的 VLC 播放列表）。

这是我需要的四种方法：

//queue is a C-based data structure

-(NSInteger)outlineView:(NSOutlineView *)outlineView numberOfChildrenOfItem:(id)item
{
    if(item == nil){
        return queue.count; //each list item
    }else{
        return 0; //no children of each list item allowed
    }
}

-(id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item
{
    if(item != nil) return nil;

    return [[NSDictionary dictionaryWithObjectsAndKeys:
             [NSNumber numberWithLong:index],@"index",
             [NSString stringWithFormat:@"%s",queue.item[index].filepath],@"filePath",
             nil] copy];
}

-(BOOL)outlineView:(NSOutlineView *)outlineView isItemExpandable:(id)item
{
    if(item == nil){
        return YES;
    }else{
        return NO;
    }
}

-(id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item
{
    if(item == nil) return nil;

    return [item objectForKey:[tableColumn identifier]];
}

还有我的拖动方法：

-(BOOL)outlineView:(NSOutlineView *)outlineView writeItems:(NSArray *)items toPasteboard:(NSPasteboard *)pasteboard
{
    [pasteboard declareTypes:[NSArray arrayWithObject:LOCAL_REORDER_PASTEBOARD_TYPE] owner:self];
    [pasteboard setData:[NSData data] forType:LOCAL_REORDER_PASTEBOARD_TYPE];
    return YES;
}

-(NSDragOperation)outlineView:(NSOutlineView *)outlineView validateDrop:(id <NSDraggingInfo>)info proposedItem:(id)item proposedChildIndex:(NSInteger)index
{
    NSUInteger op = NSDragOperationNone;

    if(index != NSOutlineViewDropOnItemIndex){
        op = NSDragOperationMove;
    }
    return op;
}

Answer 1