Listbox drag-reorder : 拖放项的索引 [英] Listbox drag-reorder : Index of the dropped item

问题描述

我正在使用包装在 ListBoxDragDropTarget 中的 Listbox(来自 Silverlight 工具包).这个 ListBox 可以由用户手动重新排序.但是最后一项必须始终位于 ListBox 的底部，并且根本不能移动.我找到了一种取消最后一项移动的方法，但是如果我将另一个项目拖放到最后一项下方，它就会被移动.

I'm using a Listbox wrapped inside a ListBoxDragDropTarget (from the Silverlight toolkit). This ListBox ca be manually reordered by the user. However the last item must always be located at the bottom of the ListBox, and can't be moved at all. I found a way to cancel this last item moves, but if I drag and drop another item below this last item, it gets moved.

我可以在ListBox的Drop事件中使用这段代码找到被拖动项的索引:

I can find the index of the dragged item using this code in the Drop event of the ListBox:

object data = e.Data.GetData(e.Data.GetFormats()[0]);

ItemDragEventArgs dragEventArgs = data as ItemDragEventArgs;
SelectionCollection selectionCollection = dragEventArgs.Data as SelectionCollection;
if (selectionCollection != null)
{
    MyClass cw = selectionCollection[0].Item as MyClass;
    int idx = selectionCollection[0].Index.Value;   
}

但是，这只会在拖动操作之前为我提供索引.

However this only gives me the index before the drag operation.

我的问题如下:有没有办法知道被丢弃项目的 new 索引?这样，如果 index = 列表的最后一个位置，我可以将它移动到最前面的位置.

My question is the following: Is there a way to know the new index of the dropped item ? This way, if the index = last position of the list, I can move it to the forelast position.

提前致谢！

推荐答案

好的，我找到了一种方法.我绑定了 ListBoxDragDropTarget 的 ItemDragCompleted 事件，做了如下操作:

Ok I found a way to do this. I bound the ItemDragCompleted event of the ListBoxDragDropTarget, and did the following:

private void dropTarget1_ItemDragCompleted(object sender, ItemDragEventArgs e)
{
    var tmp = (e.DragSource as ListBox).ItemsSource.Cast<MyClass>().ToList();

    SelectionCollection selectionCollection = e.Data as SelectionCollection;
    if (selectionCollection != null)
    {
        MyClass cw = selectionCollection[0].Item as MyClass;

        int idx = tmp.IndexOf(cw);
        if (idx == tmp.Count - 1)
        {
            tmp.Remove(cw);
            tmp.Insert(tmp.Count - 1, cw);

            MyListBox.ItemsSource = new ObservableCollection<MyClass>(tmp);
        }
}

}

由于 DragSource 代表列表框，使用新的项目排列"，因此我可以检查项目现在是否位于末尾，并在这种情况下移动它.

As the DragSource represents the Listbox, with the new "arrangement" of items, I can therefore check if the item is now located at the end, and move it in this case.

剩下的唯一问题是它会导致屏幕闪烁，因为项目被放下然后移动.

The only problem left is that it causes a flicker on the screen, due to the item being dropped and then moved.

我仍然愿意接受任何其他(最佳)建议.

I'm still open to any other (best) suggestion.

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