ListViewInsertionMark.NearestIndex(Point) 方法

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

检索距离指定点最近的项的索引。

public:
 int NearestIndex(System::Drawing::Point pt);

public int NearestIndex (System.Drawing.Point pt);

member this.NearestIndex : System.Drawing.Point -> int

Public Function NearestIndex (pt As Point) As Integer

参数

pt

Point

从 Point 表示的位置找到最近的项。

返回

Int32

距离指定点最近的项的索引；如果最近的项就是当前被拖动的项，则为 -1。

示例

下面的代码示例演示如何使用 ListView 插入标记功能，并使用标准拖动事件实现拖放项重新排序。 插入标记的位置在 事件的处理程序 Control.DragOver 中更新。 在此处理程序中，将鼠标指针的位置与最近的项的中点进行比较，并使用结果来确定插入标记是显示在项的左侧还是右侧。

有关完整示例，请参阅 ListViewInsertionMark 概述参考主题。

// Moves the insertion mark as the item is dragged.
void myListView_DragOver( Object^ /*sender*/, DragEventArgs^ e )
{
   // Retrieve the client coordinates of the mouse pointer.
   Point targetPoint = myListView->PointToClient( Point(e->X,e->Y) );

   // Retrieve the index of the item closest to the mouse pointer.
   int targetIndex = myListView->InsertionMark->NearestIndex( targetPoint );

   // Confirm that the mouse pointer is not over the dragged item.
   if ( targetIndex > -1 )
   {
      // Determine whether the mouse pointer is to the left or
      // the right of the midpoint of the closest item and set
      // the InsertionMark.AppearsAfterItem property accordingly.
      Rectangle itemBounds = myListView->GetItemRect( targetIndex );
      if ( targetPoint.X > itemBounds.Left + (itemBounds.Width / 2) )
      {
         myListView->InsertionMark->AppearsAfterItem = true;
      }
      else
      {
         myListView->InsertionMark->AppearsAfterItem = false;
      }
   }

   // Set the location of the insertion mark. If the mouse is
   // over the dragged item, the targetIndex value is -1 and
   // the insertion mark disappears.
   myListView->InsertionMark->Index = targetIndex;
}

// Moves the insertion mark as the item is dragged.
private void myListView_DragOver(object sender, DragEventArgs e)
{
    // Retrieve the client coordinates of the mouse pointer.
    Point targetPoint = 
        myListView.PointToClient(new Point(e.X, e.Y));

    // Retrieve the index of the item closest to the mouse pointer.
    int targetIndex = myListView.InsertionMark.NearestIndex(targetPoint);

    // Confirm that the mouse pointer is not over the dragged item.
    if (targetIndex > -1) 
    {
        // Determine whether the mouse pointer is to the left or
        // the right of the midpoint of the closest item and set
        // the InsertionMark.AppearsAfterItem property accordingly.
        Rectangle itemBounds = myListView.GetItemRect(targetIndex);
        if ( targetPoint.X > itemBounds.Left + (itemBounds.Width / 2) )
        {
            myListView.InsertionMark.AppearsAfterItem = true;
        }
        else
        {
            myListView.InsertionMark.AppearsAfterItem = false;
        }
    }

    // Set the location of the insertion mark. If the mouse is
    // over the dragged item, the targetIndex value is -1 and
    // the insertion mark disappears.
    myListView.InsertionMark.Index = targetIndex;
}

' Moves the insertion mark as the item is dragged.
Private Sub myListView_DragOver(sender As Object, e As DragEventArgs)
    ' Retrieve the client coordinates of the mouse pointer.
    Dim targetPoint As Point = myListView.PointToClient(New Point(e.X, e.Y))
    
    ' Retrieve the index of the item closest to the mouse pointer.
    Dim targetIndex As Integer = _
        myListView.InsertionMark.NearestIndex(targetPoint)
    
    ' Confirm that the mouse pointer is not over the dragged item.
    If targetIndex > -1 Then
        ' Determine whether the mouse pointer is to the left or
        ' the right of the midpoint of the closest item and set
        ' the InsertionMark.AppearsAfterItem property accordingly.
        Dim itemBounds As Rectangle = myListView.GetItemRect(targetIndex)
        If targetPoint.X > itemBounds.Left + (itemBounds.Width / 2) Then
            myListView.InsertionMark.AppearsAfterItem = True
        Else
            myListView.InsertionMark.AppearsAfterItem = False
        End If
    End If
    
    ' Set the location of the insertion mark. If the mouse is
    ' over the dragged item, the targetIndex value is -1 and
    ' the insertion mark disappears.
    myListView.InsertionMark.Index = targetIndex
End Sub

注解

使用此方法，可以在执行拖放操作时查找离鼠标指针最近的项。 使用返回的索引值设置 Index 属性。 当最接近鼠标指针的项是正在拖动的项时，此方法的返回值为 -1。 在这种情况下，将 Index 属性设置为此值将隐藏插入标记。

无论鼠标指针位于何处，此方法都会查找最接近的项，而 ListView.GetItemAt 该方法仅返回指定位置处的项，或者 null 如果该位置没有项，则返回该项。 方法 ListView.GetItemAt 返回 null，例如，当鼠标指针位于两个项之间时。 因此，在使用拖放操作定位项时，应始终使用 NearestIndex 方法。

另请参阅

• ListView