PreviewMouseLeftButtonDown干擾點擊選擇

Question

我已經實現了這個代碼來執行列表框中的拖動功能。

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

但意識到事件PreviewMouseLeftButtonDown與CLIC選擇干擾。所以當我想選擇一個項目時，我必須在項目中進行兩次點擊。

我應該修改什麼來修復該錯誤？

Answer 1

爲避免干擾正常選擇，通常在用戶通過DragDrop.DoDragDrop（）實際執行拖放操作之前，讓用戶拖動一個項目幾個像素（正是這種調用會中斷正常的點擊選擇你的例子）。要做到這一點

的方法之一是擴大你的例子一點，並通過監聽ListBox的PreviewMouseMove和的PreviewMouseLeftButtonUp事件跟蹤一個「潛在拖」的，除了的PreviewMouseLeftButtonDown事件：

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

注意我們如何使用potentialDragStartPoint這裏，怎麼了大量的代碼是從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; 
     } 
    } 
}