Question

我正在开发一个Wpf项目，但是现在我遇到了ListView问题。

事实证明我在ListView上实现了Drag&Drop功能，工作正常。当我尝试向下或向上滚动时出现问题。通过这样做，Drag&Drop功能被激活，阻止我保持滚动。

我发现this solution表示我们需要将控件附加到ScrollChanged事件。

<ListView ScrollViewer.ScrollChanged="listView1_ScrollChanged"...

但我真的不知道该处理程序该怎么做。 如何禁用该事件的拖放功能？我怎么能再次启用它？或者，有没有更好的方法来解决这个问题？

这是我的Drag&Drop代码：

 private void listView1_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        // Store the mouse position
        startPoint = e.GetPosition(null);
    }

    private void listView1_MouseMove(object sender, MouseEventArgs e)
    {
        // Get the current mouse position
        Point mousePos = e.GetPosition(null);
        Vector diff = startPoint - mousePos;

        if (e.LeftButton == MouseButtonState.Pressed &&
            (Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance ||
            Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance))
        {
            // Get the dragged ListViewItem
            ListView listView = sender as ListView;

            // Get items to drag
            var a = listView.SelectedItems;

            // Initialize the drag & drop operation
            DataObject dragData = new DataObject("myFormat", a);
            DragDrop.DoDragDrop(listView, dragData, DragDropEffects.Move);
        } 
    }

提前致谢。

Answer 1

如果您不在MouseDown事件中，则可以阻止MouseMove事件：

bool stopDrag = true;
     private void listView1_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            // Store the mouse position
            startPoint = e.GetPosition(null);
stopDrag = false;
        }

        private void listView1_MouseMove(object sender, MouseEventArgs e)
        {
if(stopDrag)
   return;

            // Get the current mouse position
            Point mousePos = e.GetPosition(null);
            Vector diff = startPoint - mousePos;

            if (e.LeftButton == MouseButtonState.Pressed &&
                (Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance ||
                Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance))
            {
                // Get the dragged ListViewItem
                ListView listView = sender as ListView;

                // Get items to drag
                var a = listView.SelectedItems;

                // Initialize the drag & drop operation
                DataObject dragData = new DataObject("myFormat", a);
                DragDrop.DoDragDrop(listView, dragData, DragDropEffects.Move);
            } 
        }

private void listView1_MouseUp(...)
{
stopDrag = true;
}

这应该有用，我在浏览器中写了这个，请原谅我，如果我做错了什么，格式化，我希望你有这个想法。

Answer 2

我使用一种简单的方法来确认是否使用为此目的而制作的SystemParameters.MinimumHorizontalDragDistance和SystemParameters.MinimumVerticalDragDistance确认了拖动操作：

private bool IsDragConfirmed(Point point)
{
    bool horizontalMovement = Math.Abs(point.X - dragStartPosition.X) > 
         SystemParameters.MinimumHorizontalDragDistance;
    bool verticalMovement = Math.Abs(point.Y - dragStartPosition.Y) > 
         SystemParameters.MinimumVerticalDragDistance;
    return (horizontalMovement | verticalMovement);
}

在PreviewMouseMove事件中调用...这是一个简化示例：

private void DragSourcePreviewMouseMove(object sender, MouseEventArgs e)
{
    if (isMouseDown && IsDragConfirmed(e.GetPosition(sender as ListBox)))
    {
        // Start your drag operation here
    }
}

Answer 3

我得到了与下面答案相同的问题和相同的来源。好吧，如果鼠标位置不在listview项目上，我决定阻止拖动（rect 0,0，lv.width - scroll.width，lv.height - scroll.height）所以我有一个＆＃34; allowdrag＆＃34; flag，当PreviewMouseLeftButtonDown过去时，如果鼠标指针超过必要的矩形，则变为True。

VB.NET

Private allowdrag As Boolean

Private Sub lv_PreviewMouseLeftButtonDown(sender As Object, e As MouseButtonEventArgs) Handles lvAttributesDefault.PreviewMouseLeftButtonDown
    Dim listView As ListView = TryCast(sender, ListView)
    allowdrag = e.GetPosition(sender).X < listView.ActualWidth - SystemParameters.VerticalScrollBarWidth And e.GetPosition(sender).Y < listView.ActualHeight - SystemParameters.HorizontalScrollBarHeight
End Sub

Private Sub lv_MouseMove(sender As Object, e As MouseEventArgs) Handles lvAttributesDefault.MouseMove
    Dim listView As ListView = TryCast(sender, ListView)

    If e.LeftButton = MouseButtonState.Pressed And listView.SelectedItem IsNot Nothing And allowdrag Then
        Dim obj As clsAttribute = CType(listView.SelectedItem, clsAttribute)
        Dim dragData As New DataObject("clsAttribute", obj)

        DragDrop.DoDragDrop(listView, dragData, DragDropEffects.Copy)
    End If
End Sub

C＃（telerik代码转换器）

private bool allowdrag;
private void lv_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    ListView listView = sender as ListView;
    allowdrag = e.GetPosition(sender).X < listView.ActualWidth - SystemParameters.VerticalScrollBarWidth & e.GetPosition(sender).Y < listView.ActualHeight - SystemParameters.HorizontalScrollBarHeight;
}

private void lv_MouseMove(object sender, MouseEventArgs e)
{
    ListView listView = sender as ListView;

    if (e.LeftButton == MouseButtonState.Pressed & listView.SelectedItem != null & allowdrag) {
        clsAttribute obj = (clsAttribute)listView.SelectedItem;
        DataObject dragData = new DataObject("clsAttribute", obj);

        DragDrop.DoDragDrop(listView, dragData, DragDropEffects.Copy);
    }
}

PS。 clsAttribute是我的自定义类。该 listview绑定到ObservableCollection（Of clsAttribute）

防止拖拽;滚动时丢弃

3 个答案: