你必须像这样显式地这样做：

<Button>
    <Button.Content>
        <TextBlock>
            My <Underline>C</Underline>ontent
        </TextBlock>
    </Button.Content>
</Button>

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这将删除使用Alt+Char单击按钮的功能。为此，使用AccessText元素。但它不支持TextBlock的标记语法。

如果添加了绑定，则可以使用Alt+Char保留单击按钮的功能。在我的例子中，我使用Alt+X退出（关闭）当前窗口

public class RelayCommand : ICommand
{
    private readonly Action _execute;

    public event EventHandler CanExecuteChanged;

    public RelayCommand(Action execute)
    {
        _execute = execute;
    }

    public bool CanExecute(object parameter)
    {
        return true;
    }

    public void Execute(object parameter)
    {
        _execute?.Invoke();
    }
}
public partial class Window : Window
{

    public ICommand ExitCommand { get; }
    public Window()
    {
        InitializeComponent();

        ExitCommand = new RelayCommand(ExitApplication);
        CommandBindings.Add(new CommandBinding(ExitCommand, ExecuteExitCommand, CanExecuteExitCommand));

        KeyGesture exitKeyGesture = new KeyGesture(Key.X, ModifierKeys.Alt);
        InputBindings.Add(new KeyBinding(ExitCommand, exitKeyGesture));

    }
    private void ExecuteExitCommand(object sender, ExecutedRoutedEventArgs e)
    {
        ExitApplication();
    }
    private void CanExecuteExitCommand(object sender, CanExecuteRoutedEventArgs e)
    {
        e.CanExecute = true;
    }
    private void ExitApplication()
    {
        Close();
    }
    private void exitbutton_Click(object sender, RoutedEventArgs e)
    {
        ExitApplication();
    }
}

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确保您也使用System.Windows.Input进行初始化;