The ListView control does not support drag-and-drop functionality for items at run time

Symptoms

If you add items to the ListView control on a Microsoft Windows form, you cannot reorder the items by dragging the items in the ListView control at run time.

Cause

This problem occurs because the ListView control does not support drag-and-drop functionality for the items at run time.

Workaround

To work around this problem, provide drag-and-drop functionality to the ListView control as follows:
  1. Add the following code to the
    ListView1_ItemDrag event handler.

    Microsoft Visual Basic .NET or Microsoft Visual Basic 2005 code
     'Begins a drag-and-drop operation in the ListView control.
    ListView1.DoDragDrop(ListView1.SelectedItems, DragDropEffects.Move)
    Microsoft Visual C# .NET or Microsoft Visual C# 2005 code
    //Begins a drag-and-drop operation in the ListView control.
    listView1.DoDragDrop(listView1.SelectedItems, DragDropEffects.Move);
  2. Add the following code to the
    ListView1_DragEnter event handler.

    Visual Basic .NET or Visual Basic 2005 code
    Dim i As Integer
    For i = 0 To e.Data.GetFormats().Length - 1
    If e.Data.GetFormats()(i).Equals("System.Windows.Forms.ListView+SelectedListViewItemCollection") Then
    'The data from the drag source is moved to the target.
    e.Effect = DragDropEffects.Move
    End If
    Next
    Visual C# .NET or Visual C# 2005 code
    int len=e.Data.GetFormats().Length-1 ;
    int i;
    for (i = 0 ; i<=len ;i++)
    {
    if (e.Data.GetFormats()[i].Equals("System.Windows.Forms.ListView+SelectedListViewItemCollection"))
    {
    //The data from the drag source is moved to the target.
    e.Effect = DragDropEffects.Move;
    }
    }
  3. Add the following code to the
    ListView1_DragDrop event handler.

    Visual Basic .NET or Visual Basic 2005 code
    'Return if the items are not selected in the ListView control.
    If ListView1.SelectedItems.Count = 0 Then Return
    'Returns the location of the mouse pointer in the ListView control.
    Dim p As Point = ListView1.PointToClient(New Point(e.X, e.Y))
    'Obtain the item that is located at the specified location of the mouse pointer.
    Dim dragToItem As ListViewItem = ListView1.GetItemAt(p.X, p.Y)
    If dragToItem Is Nothing Then Return
    'Obtain the index of the item at the mouse pointer.
    Dim dragIndex As Integer = dragToItem.Index
    Dim i As Integer
    Dim sel(ListView1.SelectedItems.Count) As ListViewItem
    For i = 0 To ListView1.SelectedItems.Count - 1
    sel(i) = ListView1.SelectedItems.Item(i)
    Next
    For i = 0 To ListView1.SelectedItems.Count - 1
    'Obtain the ListViewItem to be dragged to the target location.
    Dim dragItem As ListViewItem = sel(i)
    Dim itemIndex As Integer = dragIndex
    If itemIndex = dragItem.Index Then Return
    If dragItem.Index < itemIndex Then
    itemIndex = itemIndex + 1
    Else
    itemIndex = dragIndex + i
    End If
    'Insert the item in the specified location.
    Dim insertitem As ListViewItem = dragItem.Clone
    ListView1.Items.Insert(itemIndex, insertitem)
    'Removes the item from the initial location while
    'the item is moved to the new location.
    ListView1.Items.Remove(dragItem)
    Next
    Visual C# .NET or Visual C# 2005 code
    //Return if the items are not selected in the ListView control.
    if(listView1.SelectedItems.Count==0)
    {
    return;
    }
    //Returns the location of the mouse pointer in the ListView control.
    Point cp = listView1.PointToClient(new Point(e.X, e.Y));
    //Obtain the item that is located at the specified location of the mouse pointer.
    ListViewItem dragToItem = listView1.GetItemAt(cp.X, cp.Y);
    if(dragToItem==null)
    {
    return;
    }
    //Obtain the index of the item at the mouse pointer.
    int dragIndex = dragToItem.Index;
    ListViewItem[] sel=new ListViewItem [listView1.SelectedItems.Count];
    for(int i=0; i<=listView1.SelectedItems.Count-1;i++)
    {
    sel[i]=listView1.SelectedItems[i];
    }
    for(int i=0; i<sel.GetLength(0);i++)
    {
    //Obtain the ListViewItem to be dragged to the target location.
    ListViewItem dragItem = sel[i];
    int itemIndex = dragIndex;
    if(itemIndex==dragItem.Index)
    {
    return;
    }
    if(dragItem.Index<itemIndex)
    itemIndex++;
    else
    itemIndex=dragIndex+i;
    //Insert the item at the mouse pointer.
    ListViewItem insertItem = (ListViewItem)dragItem.Clone();
    listView1.Items.Insert(itemIndex, insertItem);
    //Removes the item from the initial location while
    //the item is moved to the new location.
    listView1.Items.Remove(dragItem);
    }
  4. On the Build menu, click Build Solution.
  5. On the Debug menu, click
    Start.

Status

This behavior is by design.

More Information

Steps to Reproduce the Behavior

  1. Start Microsoft Visual Studio .NET or Microsoft Visual Studio 2005.
  2. Create a new Windows application by using Visual Basic .NET, Visual Basic 2005, Visual C# 2005, or Visual C# .NET.

    By default, Form1 is created.
  3. Add the ListView control to Form1.
  4. Right-click ListView1, and then click
    Properties.
  5. In the Properties dialog box, click the
    Items property, and then click the ellipsis button (...).
  6. In the ListViewItem Collection Editordialog box, click Add four times.
  7. Set the Text property of the first ListViewItem control to Item1, set the
    Text property of the second ListViewItem control to
    Item2, set the Text property of the third
    ListViewItem control to Item3, and then set the
    Text property of the fourth ListViewItem control to
    Item4.
  8. In the ListViewItem Collection Editordialog box, click OK.
  9. In the Properties dialog box of
    ListView1, set the View property to
    List.
  10. Set the AllowDrop property of
    ListView1 to True.
  11. On the Build menu, click Build Solution.
  12. On the Debug menu, click
    Start.
  13. Try to drag Item1 to a new location in the ListView control.

    You cannot drag Item1.

References

For more information, visit the following Microsoft Web sites: For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
822482 HOW TO: Provide Drag-and-Drop Functionality in Microsoft Windows Applications by Using Microsoft Visual Basic .NET


Propriedades

ID do Artigo: 822483 - Última Revisão: 11 de jul de 2008 - Revisão: 1

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