PreviewMouseLeftButtonDown干扰点击选择

Question

我已经实现了这个代码来执行列表框中的拖动功能。

http://www.c-sharpcorner.com/uploadfile/dpatra/drag-and-drop-item-in-listbox-in-wpf/

但意识到事件PreviewMouseLeftButtonDown与CLIC选择干扰。所以当我想选择一个项目时，我必须在项目中进行两次点击。

我应该修改什么来修复该错误？

Answer 1

为避免干扰正常选择，通常在用户通过DragDrop.DoDragDrop（）实际执行拖放操作之前，让用户拖动一个项目几个像素（正是这种调用会中断正常的点击选择你的例子）。要做到这一点

的方法之一是扩大你的例子一点，并通过监听ListBox的PreviewMouseMove和的PreviewMouseLeftButtonUp事件跟踪一个“潜在拖”的，除了的PreviewMouseLeftButtonDown事件：

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

注意我们如何使用potentialDragStartPoint这里，怎么了大量的代码是从ListBox_PreviewMouseLeftButtonDown移到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; 
     } 
    } 
}