滚动时防止拖放

本文关键字：拖放 滚动 | 更新日期: 2023-09-27 18:35:42

我正在做一个 Wpf 项目，但现在我遇到了一个ListView问题。

事实证明，我已经在ListView上实现了Drag&Drop功能，该功能运行良好。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。

我找到了这个解决方案，它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怎么做。如何从该事件中禁用拖放？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);
        } 
    }

提前谢谢。

滚动时防止拖放

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;
}

这应该有效，我在浏览器中写了它，所以如果我做错了什么，请原谅我，对于格式，我希望你明白了。

我使用一个简单的方法来确认拖动操作是否得到确认，使用为此目的而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事件中被称为...下面是一个简化的示例：

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

我遇到了与以下答案相同的问题和相同的来源。好吧，我决定防止拖动，如果鼠标位置不在列表视图项目上（矩形 0， 0， lv.width - scroll.width， lv.height - scroll.height）所以我有一个"allowdrag"标志，如果在 PreviewMouseLeftButtonDown 经过时鼠标指针位于必要的矩形上，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 code converter）

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);
    }
}

clsAttribute 是我的自定义类。这listview 绑定到 ObservableCollection（of clsAttribute）

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