ListViewInsertionMark.NearestIndex(Point) 方法

定義

命名空間:

System.Windows.Forms

組件:

System.Windows.Forms.dll

來源:

ListViewInsertionMark.cs

擷取最接近指定點的項目索引。

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

參數

pt

Point

Point，表示要從此位置尋找最接近的項目。

傳回

Int32

最接近指定點的項目索引，如果最接近的項目是目前正在拖曳的項目，則為 -1。

範例

下列程式碼範例示範如何使用 ListView 插入標記功能，並使用標準拖曳事件來實作拖放專案重新排序。 插入標記的位置會在事件的處理常式 Control.DragOver 中更新。 在此處理程式中，滑鼠指標的位置會與最接近專案的中間點進行比較，而結果會用來判斷插入標記是否出現在專案的左邊或右邊。

如需完整的範例，請參閱 ListViewInsertionMark 概觀參考主題。

// 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

備註

這個方法可讓您在執行拖放作業時，找出最接近滑鼠指標的專案。 使用傳回的索引值來設定 Index 屬性。 當最接近滑鼠指標的專案是要拖曳的專案時，這個方法的傳回值為 -1。 在此情況下，將 屬性設定 Index 為這個值會隱藏插入標記。

這個方法會尋找最接近的專案，不論滑鼠指標位於何處，而 ListView.GetItemAt 方法只會傳回位於指定位置的專案，或 null 如果該位置沒有專案。 方法 ListView.GetItemAt 會傳 null 回 ，例如，當滑鼠指標位於兩個專案之間時。 基於這個理由，使用拖放作業來放置專案時，您應該一律使用 NearestIndex 方法。

另請參閱

• ListView