如何获取Silverlight应用程序中的拖动元素

Question

我有两个ListBox（在Silverlight 3应用程序中），每个ListBox都包含一个ListBoxDragDropTarget。 现在我用一些自定义对象（Person）填充SourceBox。 然后，我连接目标DragDtopTarget的DragOver事件。 这一切工作正常，我可以拖动&从第一个列表中删除元素到第二个。

现在我的问题：我怎样才能得到的元素，这是被拖动，以允许/不赞拖动？ （我无法从FragEventArgs中获取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处理程序的代码：

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 

感谢您的任何提示如何解决这个问题。

克里斯托夫

编辑：

这是我的应答:-)的短版：

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，然后检索SelectionCollection从它，其中包含您拖动的项目。将你的e参数传递给这个方法，它应该返回你拖动的项目。

我用一个在线的C＃到VB转换器，所以希望它做了足够好的工作。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