DragEventHandler 代理人

參考

定義

命名空間:: System.Windows.Forms

組件:: System.Windows.Forms.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

表示處理 DragDrop 之 DragEnter、DragOver 或 Control 事件的方法。

public delegate void DragEventHandler(System::Object ^ sender, DragEventArgs ^ e);

public delegate void DragEventHandler(object sender, DragEventArgs e);

public delegate void DragEventHandler(object? sender, DragEventArgs e);

type DragEventHandler = delegate of obj * DragEventArgs -> unit

Public Delegate Sub DragEventHandler(sender As Object, e As DragEventArgs)

參數

sender: Object

事件的來源。

e: DragEventArgs

DragEventArgs，其中包含事件資料。

範例

下列範例示範兩 ListBox 個控制項之間的拖放作業。範例會在拖曳動作啟動時呼叫 DoDragDrop 方法。如果滑鼠在事件期間 MouseDown 從滑鼠位置移動超過 SystemInformation.DragSize ，拖曳動作就會開始。方法 IndexFromPoint 可用來判斷事件期間 MouseDown 要拖曳之專案的索引。

此範例也會示範如何針對拖放作業使用自訂資料指標。此範例假設應用程式目錄中分別存在自訂拖放資料指標的兩個數據指標檔案 3dwarro.cur 和 3dwno.cur 。如果已核取， UseCustomCursorsCheckCheckBox 則會使用自訂資料指標。自訂資料指標是在事件處理常式中 GiveFeedback 設定。

鍵盤狀態會在右側 ListBox 的 DragOver 事件處理常式中評估，以判斷拖曳作業會根據 SHIFT、CTRL、ALT 或 CTRL+ALT 鍵的狀態而定。在事件期間 DragOver 也會決定置放位置中的位置 ListBox 。如果要卸載的資料不是 String ，則會 DragEventArgs.Effect 將設定為 DragDropEffects.None 。最後，卸載的狀態會顯示在中 DropLocationLabelLabel 。

要為右邊 ListBox 卸載的資料是在事件處理常式中 DragDrop 決定， String 而且值會加入至中 ListBox 適當的位置。如果拖曳作業在表單界限之外移動，則會在事件處理常式中 QueryContinueDrag 取消拖放作業。

此程式碼摘錄示範如何搭配 DragOver 事件使用 DragEventHandler 委派。如需完整的程式碼範例， DoDragDrop 請參閱方法。

void ListDragTarget_DragOver( Object^ /*sender*/, System::Windows::Forms::DragEventArgs^ e )
{
   // Determine whether string data exists in the drop data. If not, then
   // the drop effect reflects that the drop cannot occur.
   if (  !e->Data->GetDataPresent( System::String::typeid ) )
   {
      e->Effect = DragDropEffects::None;
      DropLocationLabel->Text = "None - no string data.";
      return;
   }

   // Set the effect based upon the KeyState.
   if ( (e->KeyState & (8 + 32)) == (8 + 32) && ((e->AllowedEffect & DragDropEffects::Link) == DragDropEffects::Link) )
   {
      // KeyState 8 + 32 = CTRL + ALT
      // Link drag-and-drop effect.
      e->Effect = DragDropEffects::Link;
   }
   else
   if ( (e->KeyState & 32) == 32 && ((e->AllowedEffect & DragDropEffects::Link) == DragDropEffects::Link) )
   {
      // ALT KeyState for link.
      e->Effect = DragDropEffects::Link;
   }
   else
   if ( (e->KeyState & 4) == 4 && ((e->AllowedEffect & DragDropEffects::Move) == DragDropEffects::Move) )
   {
      // SHIFT KeyState for move.
      e->Effect = DragDropEffects::Move;
   }
   else
   if ( (e->KeyState & 8) == 8 && ((e->AllowedEffect & DragDropEffects::Copy) == DragDropEffects::Copy) )
   {
      // CTRL KeyState for copy.
      e->Effect = DragDropEffects::Copy;
   }
   else
   if ( (e->AllowedEffect & DragDropEffects::Move) == DragDropEffects::Move )
   {
      // By default, the drop action should be move, if allowed.
      e->Effect = DragDropEffects::Move;
   }
   else
            e->Effect = DragDropEffects::None;





   
   // Get the index of the item the mouse is below.
   // The mouse locations are relative to the screen, so they must be
   // converted to client coordinates.
   indexOfItemUnderMouseToDrop = ListDragTarget->IndexFromPoint( ListDragTarget->PointToClient( Point(e->X,e->Y) ) );
   
   // Updates the label text.
   if ( indexOfItemUnderMouseToDrop != ListBox::NoMatches )
   {
      DropLocationLabel->Text = String::Concat( "Drops before item # ", (indexOfItemUnderMouseToDrop + 1) );
   }
   else
            DropLocationLabel->Text = "Drops at the end.";
}

private void ListDragTarget_DragOver(object sender, DragEventArgs e)
{
    // Determine whether string data exists in the drop data. If not, then
    // the drop effect reflects that the drop cannot occur.
    if (!e.Data.GetDataPresent(typeof(System.String)))
    {
        e.Effect = DragDropEffects.None;
        DropLocationLabel.Text = "None - no string data.";
        return;
    }

    // Set the effect based upon the KeyState.
    if ((e.KeyState & (8 + 32)) == (8 + 32) &&
        (e.AllowedEffect & DragDropEffects.Link) == DragDropEffects.Link)
    {
        // KeyState 8 + 32 = CTRL + ALT

        // Link drag-and-drop effect.
        e.Effect = DragDropEffects.Link;
    }
    else if ((e.KeyState & 32) == 32 &&
        (e.AllowedEffect & DragDropEffects.Link) == DragDropEffects.Link)
    {
        // ALT KeyState for link.
        e.Effect = DragDropEffects.Link;
    }
    else if ((e.KeyState & 4) == 4 &&
        (e.AllowedEffect & DragDropEffects.Move) == DragDropEffects.Move)
    {
        // SHIFT KeyState for move.
        e.Effect = DragDropEffects.Move;
    }
    else if ((e.KeyState & 8) == 8 &&
        (e.AllowedEffect & DragDropEffects.Copy) == DragDropEffects.Copy)
    {
        // CTRL KeyState for copy.
        e.Effect = DragDropEffects.Copy;
    }
    else if ((e.AllowedEffect & DragDropEffects.Move) == DragDropEffects.Move)
    {
        // By default, the drop action should be move, if allowed.
        e.Effect = DragDropEffects.Move;
    }
    else
    {
        e.Effect = DragDropEffects.None;
    }

    // Get the index of the item the mouse is below. 

    // The mouse locations are relative to the screen, so they must be 
    // converted to client coordinates.

    indexOfItemUnderMouseToDrop =
        ListDragTarget.IndexFromPoint(ListDragTarget.PointToClient(new Point(e.X, e.Y)));

    // Updates the label text.
    if (indexOfItemUnderMouseToDrop != ListBox.NoMatches)
    {
        DropLocationLabel.Text = "Drops before item #" + (indexOfItemUnderMouseToDrop + 1);
    }
    else
    {
        DropLocationLabel.Text = "Drops at the end.";
    }
}

Private Sub ListDragTarget_DragOver(ByVal sender As Object, ByVal e As DragEventArgs) Handles ListDragTarget.DragOver
    ' Determine whether string data exists in the drop data. If not, then
    ' the drop effect reflects that the drop cannot occur.
    If Not (e.Data.GetDataPresent(GetType(System.String))) Then

        e.Effect = DragDropEffects.None
        DropLocationLabel.Text = "None - no string data."
        Return
    End If

    ' Set the effect based upon the KeyState.
    If ((e.KeyState And (8 + 32)) = (8 + 32) And
        (e.AllowedEffect And DragDropEffects.Link) = DragDropEffects.Link) Then
        ' KeyState 8 + 32 = CTRL + ALT

        ' Link drag-and-drop effect.
        e.Effect = DragDropEffects.Link

    ElseIf ((e.KeyState And 32) = 32 And
        (e.AllowedEffect And DragDropEffects.Link) = DragDropEffects.Link) Then

        ' ALT KeyState for link.
        e.Effect = DragDropEffects.Link

    ElseIf ((e.KeyState And 4) = 4 And
        (e.AllowedEffect And DragDropEffects.Move) = DragDropEffects.Move) Then

        ' SHIFT KeyState for move.
        e.Effect = DragDropEffects.Move

    ElseIf ((e.KeyState And 8) = 8 And
        (e.AllowedEffect And DragDropEffects.Copy) = DragDropEffects.Copy) Then

        ' CTRL KeyState for copy.
        e.Effect = DragDropEffects.Copy

    ElseIf ((e.AllowedEffect And DragDropEffects.Move) = DragDropEffects.Move) Then

        ' By default, the drop action should be move, if allowed.
        e.Effect = DragDropEffects.Move

    Else
        e.Effect = DragDropEffects.None
    End If

    ' Gets the index of the item the mouse is below. 

    ' The mouse locations are relative to the screen, so they must be 
    ' converted to client coordinates.

    indexOfItemUnderMouseToDrop =
        ListDragTarget.IndexFromPoint(ListDragTarget.PointToClient(New Point(e.X, e.Y)))

    ' Updates the label text.
    If (indexOfItemUnderMouseToDrop <> ListBox.NoMatches) Then
        DropLocationLabel.Text = "Drops before item #" & (indexOfItemUnderMouseToDrop + 1)
    Else
        DropLocationLabel.Text = "Drops at the end."
    End If

End Sub

備註

建立 DragEventHandler 委派時，必須識別處理事件的方法。若要使事件與您的事件處理常式產生關聯，請將委派的執行個體 (Instance) 加入至事件。除非您移除委派，否則每當事件發生時就會呼叫事件處理常式。如需使用委派處理事件的詳細資訊，請參閱處理和引發事件。

擴充方法

GetMethodInfo(Delegate)

取得表示特定委派所代表之方法的物件。

適用於

DragEventHandler 代理人

定義

參數

範例

備註

擴充方法

適用於

另請參閱

意見反應

其他資源