如何在 Silverlight 应用程序中获取拖动的元素

Question

我有两个列表框（在 Silverlight 3 应用程序中），每个列表框都包含一个 ListBoxDragDropTarget。 现在我用一些自定义对象（人）填充 SourceBox。 然后我连接目标 DragDtopTarget 的 DragOver 事件。 这一切都工作得很好，我可以拖动&将元素从第一个列表删除到第二个列表。

现在我的问题：如何获取正在拖动以允许/禁止拖动的元素？ （我无法从 FragEventArgs 获取 Person）。

这是我的 Xaml：

<Grid x:Name="LayoutRoot" Background="White">
<Grid.ColumnDefinitions>
    <ColumnDefinition Width="*"/>
    <ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>

<controlsToolkit:ListBoxDragDropTarget 
    HorizontalContentAlignment="Stretch" 
    VerticalContentAlignment="Stretch"
    x:Name="DragSource">
    <ListBox x:Name="lbSource" DisplayMemberPath="Name" />
</controlsToolkit:ListBoxDragDropTarget>

<controlsToolkit:ListBoxDragDropTarget 
    Grid.Column="1" 
    HorizontalContentAlignment="Stretch" 
    VerticalContentAlignment="Stretch"
    x:Name="DragDest"
    msWindows:DragDrop.AllowDrop="true">
    <ListBox x:Name="lbDest" DisplayMemberPath="Name" />
</controlsToolkit:ListBoxDragDropTarget>

这是我的 DragOver-Handler 的代码：

Private Sub DragDest_DragOver(ByVal sender As Object, _
   ByVal e As Microsoft.Windows.DragEventArgs) _
   Handles DragDest.DragOver

    Dim Pers = e.Data.GetData(GetType(Person))

End Sub

感谢您提供如何解决此问题的任何提示。

克里斯托夫

编辑：

这是我的答案的简短版本:-)：

Private Sub DragDest_DragOver(ByVal sender As Object, _
     ByVal e As Microsoft.Windows.DragEventArgs) _
     Handles DragDest.DragOver

    Dim Args As ItemDragEventArgs = e.Data.GetData(e.Data.GetFormats()(0))

    Dim Sel As SelectionCollection = Args.Data

    Dim Persons = (From Pe In Sel Select DirectCast(Pe.Item, Person)).ToList

End Sub

Answer 1

您需要首先将数据对象转换为 ItemDragEventArgs，然后从中检索 SelectionCollection，其中包含您拖动的项目。将您的 e 参数传递给此方法，它应该返回您拖动的项目。

我使用了一个在线 C# 到 VB 转换器，所以希望它做得足够好。下面是 VB 和 C#。

VB：

    using System.Windows.Controls;
    using System.Linq;
    using System.Collections.ObjectModel;
    using System.Collections.Generic;
#if SILVERLIGHT
    using SW = Microsoft.Windows;
#else
    using SW = System.Windows;
#endif

        Private Function GetSelectedPeople(ByVal args As SW.DragEventArgs) As IEnumerable(Of Person)
            Dim people As IEnumerable(Of Person) = Nothing
            
            ' Retrieve the dropped data in the first available format.
            Dim data As Object = args.Data.GetData(args.Data.GetFormats()(0))
            
            ' The data is the ItemDragEventArgs that was created by the DDT when
            ' the drag started.  It contains a SelectionCollection.
            ' SelectionCollection's are used by DDTs because they can transfer 
            ' multiple objects.  The fact that they store the indexes of the 
            ' objects within the source collection also makes reordering items
            ' within a source possible.
            Dim dragEventArgs As ItemDragEventArgs = TryCast(data, ItemDragEventArgs)
            Dim selectionCollection As SelectionCollection = TryCast(dragEventArgs.Data, SelectionCollection)
            If selectionCollection IsNot Nothing Then
                people = selectionCollection.[Select](Function(selection) selection.Item).OfType(Of Person)()
            End If
            
            Return people
        End Function

C#：

    using System.Windows.Controls;
    using System.Linq;
    using System.Collections.ObjectModel;
    using System.Collections.Generic;
#if SILVERLIGHT
    using SW = Microsoft.Windows;
#else
    using SW = System.Windows;
#endif

private IEnumerable<Person> GetSelectedPeople(SW.DragEventArgs args)
{
    IEnumerable<Person> people = null;

    // Retrieve the dropped data in the first available format.
    object data = args.Data.GetData(args.Data.GetFormats()[0]);

    // The data is the ItemDragEventArgs that was created by the DDT when
    // the drag started.  It contains a SelectionCollection.
    // SelectionCollection's are used by DDTs because they can transfer 
    // multiple objects.  The fact that they store the indexes of the 
    // objects within the source collection also makes reordering items
    // within a source possible.
    ItemDragEventArgs dragEventArgs = data as ItemDragEventArgs;
    SelectionCollection selectionCollection = dragEventArgs.Data as SelectionCollection;
    if (selectionCollection != null)
    {
        people = selectionCollection.Select(selection => selection.Item).OfType<Person>();
    }

    return people;
}

参考：
http://themechanicalbride.blogspot.com/ 2009/10/silverlight-drag-drop-support-part-2.html