c# - PreviewMouseLeftButtonDown 干扰点击选择

Question

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Answer 1

为避免干扰正常选择，通常让用户在通过 DragDrop.DoDragDrop() 实际执行拖放操作之前将项目拖动几个像素(在您的示例中，正是此调用中断了正常的点击选择) .

执行此操作的一种方法是稍微扩展您的示例，并通过监听 ListBox 的 PreviewMouseMove 和 PreviewMouseLeftButtonUp 事件以及 PreviewMouseLeftButtonDown 事件来跟踪“潜在拖拽”:

<ListBox x:Name="lbOne" 
         PreviewMouseLeftButtonDown="ListBox_PreviewMouseLeftButtonDown"
         PreviewMouseMove="ListBox_PreviewMouseMove"
         PreviewMouseLeftButtonUp="ListBox_PreviewMouseLeftButtonUp"
         ... />

请注意我们如何在此处使用 potentialDragStartPoint，以及如何将大量代码从 ListBox_PreviewMouseLeftButtonDown 移动到 ListBox_PreviewMouseMove:

ListBox dragSource = null;
Point? potentialDragStartPoint = null;

private void ListBox_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    if (potentialDragStartPoint == null)
    {
        ListBox parent = (ListBox)sender;
        potentialDragStartPoint = e.GetPosition(parent);
    }
}

private void ListBox_PreviewMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
    potentialDragStartPoint = null;
}

private void ListBox_PreviewMouseMove(object sender, MouseEventArgs e)
{
    if (potentialDragStartPoint == null) { return; }

    ListBox parent = (ListBox)sender;
    var dragPoint = e.GetPosition(parent);

    Vector potentialDragLength = dragPoint - potentialDragStartPoint.Value;
    if (potentialDragLength.Length > 5)
    {
        dragSource = parent;
        object data = GetDataFromListBox(dragSource, potentialDragStartPoint.Value);

        if (data != null)
        {
            DragDrop.DoDragDrop(parent, data, DragDropEffects.Move);
            potentialDragStartPoint = null;
        }
    }
}