DragEventArgs.Effect 属性

定义

获取或设置拖放操作中目标放置效果。Gets or sets the target drop effect in a drag-and-drop operation.

public:
 property System::Windows::Forms::DragDropEffects Effect { System::Windows::Forms::DragDropEffects get(); void set(System::Windows::Forms::DragDropEffects value); };
public System.Windows.Forms.DragDropEffects Effect { get; set; }
member this.Effect : System.Windows.Forms.DragDropEffects with get, set
Public Property Effect As DragDropEffects

属性值

DragDropEffects

DragDropEffects 值之一。One of the DragDropEffects values.

示例

下面的示例演示两个控件之间的拖放操作 ListBoxThe following example demonstrates a drag-and-drop operation between two ListBox controls. 该示例在 DoDragDrop 拖动操作开始时调用方法。The example calls the DoDragDrop method when the drag action starts. 如果在事件过程中鼠标移动了多个鼠标位置,则拖动操作将启动 SystemInformation.DragSize MouseDownThe drag action starts if the mouse has moved more than SystemInformation.DragSize from the mouse location during the MouseDown event. IndexFromPoint方法用于确定事件期间要拖动的项的索引 MouseDownThe IndexFromPoint method is used to determine the index of the item to drag during the MouseDown event.

该示例还演示了如何对拖放操作使用自定义光标。The example also demonstrates using custom cursors for the drag-and-drop operation. 该示例假定应用程序目录中有两个光标文件, 3dwarro.cur 3dwno.cur 分别用于自定义的拖放游标和非删除光标。The example assumes that two cursor files, 3dwarro.cur and 3dwno.cur, exist in the application directory, for the custom drag and no-drop cursors, respectively. 如果选中,则将使用自定义光标 UseCustomCursorsCheck CheckBoxThe custom cursors will be used if the UseCustomCursorsCheckCheckBox is checked. 自定义游标是在 GiveFeedback 事件处理程序中设置的。The custom cursors are set in the GiveFeedback event handler.

键盘状态在 DragOver 右侧的事件处理程序中进行计算 ListBox ,以根据 SHIFT、CTRL、ALT 或 CTRL + ALT 键确定拖动操作的状态。The keyboard state is evaluated in the DragOver event handler for the right ListBox, to determine what the drag operation will be based upon state of the SHIFT, CTRL, ALT, or CTRL+ALT keys. ListBox 事件期间也会确定放置过程中的位置 DragOverThe location in the ListBox where the drop would occur is also determined during the DragOver event. 如果要删除的数据不是,则将 String DragEventArgs.Effect 设置为 DragDropEffects.NoneIf the data to drop is not a String, then the DragEventArgs.Effect is set to DragDropEffects.None. 最后,放置的状态显示在中 DropLocationLabel LabelFinally, the status of the drop is displayed in the DropLocationLabelLabel.

要放置给权限的数据 ListBoxDragDrop 事件处理程序中确定,并将 String 值添加到中的适当位置 ListBoxThe data to drop for the right ListBox is determined in the DragDrop event handler and the String value is added at the appropriate place in the ListBox. 如果拖动操作移到窗体的边界之外,则会在事件处理程序中取消拖放操作 QueryContinueDragIf the drag operation moves outside the bounds of the form, then the drag-and-drop operation is canceled in the QueryContinueDrag event handler.

此代码摘录演示了如何使用 DragEventArgs 类。This code excerpt demonstrates using the DragEventArgs class. DoDragDrop有关完整的代码示例,请参阅方法。See the DoDragDrop method for the complete code example.

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 = CTL + 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) )
   {
      // CTL 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 = CTL + 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)
    {
        // CTL 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 = CTL + 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

        ' CTL 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

注解

默认情况下,应用的效果将决定拖放操作目标的鼠标光标。By default, the effect applied determines the mouse cursor for the target of a drag-and-drop operation. 这对于向用户提供有关将发生的操作的反馈非常有用。This is useful to provide feedback to the user on the operation that will occur. 例如,如果在从源拖动文件时按下 CTRL 键,则指定 DragDropEffects.Copy 以指示目标将尝试执行复制操作。For example, if you press the CTRL key when you drag a file from a source, specify DragDropEffects.Copy to indicate the target will try to perform a copy operation.

若要将自定义游标用于拖动操作,请参阅 GiveFeedbackEventArgs.UseDefaultCursorsTo use custom cursors for a drag operation, see GiveFeedbackEventArgs.UseDefaultCursors.

适用于

另请参阅