滚动时防止拖放

Question

我正在处理一个 Wpf 项目，但现在我遇到了 ListView 问题。

事实证明，我在 ListView 上实现了 Drag&Drop 功能，效果很好。当我尝试向下或向上滚动时，问题就来了。通过这样做，Drag&Drop 功能被激活，阻止我继续滚动。

我找到了this solution，这表明我们需要将控件附加到ScrollChanged 事件。

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

但我真的不知道在那个处理程序中该做什么。 如何禁用该事件的拖放功能？我怎样才能再次启用它？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，您可以阻止 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;
}

这应该可以，我是在浏览器中写的，如果我做错了什么，请原谅，对于格式，我希望你明白。

Answer 2

我使用了一个简单的方法来确认拖动操作是否被确认，使用为此目的制作的SystemParameters.MinimumHorizontalDragDistance和SystemParameters.MinimumVerticalDragDistance：

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);
}

它在PreviewMouseMove 事件中被调用...这是一个简化的例子：

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

Answer 3

我遇到了与以下答案相同的问题和相同的来源。 好吧，如果鼠标位置不在列表视图项目上方，我决定防止拖动（矩形 0、0、lv.width - scroll.width、lv.height - scroll.height） 所以我有一个“allowdrag”标志，如果当 PreviewMouseLeftButtonDown 过去时鼠标指针超过必要的矩形，则该标志变为 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);
    }
}

附言。 clsAttribute 是我的自定义类。这 listview 已绑定到 ObservableCollection(Of clsAttribute)