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Como: Posicionar um menu de contexto personalizado em um RichTextBox

  • Artigo

Este exemplo mostra como posicionar um menu de contexto personalizado para um RichTextBox.

Quando você implementa um menu de contexto personalizado para um RichTextBox, você é responsável por manipular o posicionamento do menu de contexto. Por padrão, um menu de contexto personalizado é aberto no centro do RichTextBox.

Adicionar um ouvinte para o evento ContextMenuOpening

Para substituir o comportamento de posicionamento padrão, adicione um listener para o evento ContextMenuOpening. O exemplo a seguir mostra como fazer isso programaticamente.

richTextBox.ContextMenuOpening += new ContextMenuEventHandler(richTextBox_ContextMenuOpening);

AddHandler richTextBox.ContextMenuOpening, AddressOf richTextBox_ContextMenuOpening

Implementação do ouvinte do evento ContextMenuOpening

O exemplo a seguir mostra uma implementação do ouvinte de eventos ContextMenuOpening correspondente.

// This method is intended to listen for the ContextMenuOpening event from a RichTextBox.
// It will position the custom context menu at the end of the current selection.
void richTextBox_ContextMenuOpening(object sender, ContextMenuEventArgs e)
{
    // Sender must be RichTextBox.
    RichTextBox rtb = sender as RichTextBox;
    if (rtb == null) return;

    ContextMenu contextMenu = rtb.ContextMenu;
    contextMenu.PlacementTarget = rtb;

    // This uses HorizontalOffset and VerticalOffset properties to position the menu,
    // relative to the upper left corner of the parent element (RichTextBox in this case).
    contextMenu.Placement = PlacementMode.RelativePoint;

    // Compute horizontal and vertical offsets to place the menu relative to selection end.
    TextPointer position = rtb.Selection.End;

    if (position == null) return;

    Rect positionRect = position.GetCharacterRect(LogicalDirection.Forward);
    contextMenu.HorizontalOffset = positionRect.X;
    contextMenu.VerticalOffset = positionRect.Y;

    // Finally, mark the event has handled.
    contextMenu.IsOpen = true;
    e.Handled = true;
}

' This method is intended to listen for the ContextMenuOpening event from a RichTextBox.
' It will position the custom context menu at the end of the current selection.
Private Sub richTextBox_ContextMenuOpening(ByVal sender As Object, ByVal e As ContextMenuEventArgs)
    ' Sender must be RichTextBox.
    Dim rtb As RichTextBox = TryCast(sender, RichTextBox)
    If rtb Is Nothing Then
        Return
    End If

    Dim contextMenu As ContextMenu = rtb.ContextMenu
    contextMenu.PlacementTarget = rtb

    ' This uses HorizontalOffset and VerticalOffset properties to position the menu,
    ' relative to the upper left corner of the parent element (RichTextBox in this case).
    contextMenu.Placement = PlacementMode.RelativePoint

    ' Compute horizontal and vertical offsets to place the menu relative to selection end.
    Dim position As TextPointer = rtb.Selection.End

    If position Is Nothing Then
        Return
    End If

    Dim positionRect As Rect = position.GetCharacterRect(LogicalDirection.Forward)
    contextMenu.HorizontalOffset = positionRect.X
    contextMenu.VerticalOffset = positionRect.Y

    ' Finally, mark the event has handled.
    contextMenu.IsOpen = True
    e.Handled = True
End Sub

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