我有一个绑定到菜单项的richtextbox，允许粗体、斜体和下划线以及剪切、复制和粘贴。但是，如何将richtextbox内容从后面的代码转换为字符串，从而携带粗体、斜体等？

</DockPanel>
            <DockPanel Height="259" VerticalAlignment="Bottom">
            <Menu DockPanel.Dock="Top">
                <MenuItem Header="Edit">
                    <MenuItem Command="Cut" Header="_Cut" />
                    <MenuItem Command="Copy" Header="C_opy" />
                    <MenuItem Command="Paste" Header="_Paste" />
                </MenuItem>
            </Menu>
            <ToolBarTray DockPanel.Dock="Top">
                <ToolBar>
                    <Button Command="Cut" Content="Cut" />
                    <Button Command="Copy" Content="Copy" />
                    <Button Command="Paste" Content="Paste" />
                            <ToggleButton MinWidth="40"
                    Command="EditingCommands.ToggleBold"
                    CommandTarget="{Binding ElementName=XAMLRichBox}"
                    TextBlock.FontWeight="Bold">B</ToggleButton>
                            <ToggleButton MinWidth="40"
                    Command="EditingCommands.ToggleItalic"
                    CommandTarget="{Binding ElementName=XAMLRichBox}"
                    TextBlock.FontStyle="Italic">I</ToggleButton>
                            <ToggleButton MinWidth="40"
                    Command="EditingCommands.ToggleUnderline"
                    CommandTarget="{Binding ElementName=XAMLRichBox}">
                                <TextBlock TextDecorations="Underline">U</TextBlock>
                            </ToggleButton>
                        </ToolBar>
            </ToolBarTray>
                <RichTextBox HorizontalAlignment="Left" Margin="0,0,0,0" Name="richTextBox1"  Height="211" VerticalAlignment="Top" Width="398" />

在后面的代码中，我试图做到这一点（不知道如何做到这一点），但文本块只是出来作为正常文本它不包含粗体等。

private void button1_Click(object sender, RoutedEventArgs e)
    {
        string myText = new TextRange(richTextBox1.Document.ContentStart, richTextBox1.Document.ContentEnd).Text;
        textBlock1.Text = myText;