Question

我已实现此代码以在listBox中执行拖动功能。

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

但是意识到事件PreviewMouseLeftButtonDown干扰了clic选择。因此，当我想选择一个项目时，我必须在项目中单击两次。

我应该修改什么来修复该错误？

Answer 1

为避免干扰正常选择，通常会让用户在通过DragDrop.DoDragDrop（）实际执行拖放操作之前将项目拖动几个像素（正是此调用会中断正常的点击选择）例子）。

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

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

注意我们如何在这里使用 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;
        }
    }
}

PreviewMouseLeftButtonDown会干扰点击选择

1 个答案: