如何在MouseEnter上为TextBlock加下划线

<TextBlock Text="Hello, world!" MouseEnter="TextBlock_MouseEnter" MouseLeave="TextBlock_MouseLeave"/>

private void TextBlock_MouseEnter(object sender, MouseEventArgs e)
{
    TextBlock textBlock = sender as TextBlock;
    textBlock.TextDecorations = TextDecorations.Underline;
}

private void TextBlock_MouseLeave(object sender, MouseEventArgs e)
{
    TextBlock textBlock = sender as TextBlock;
    textBlock.TextDecorations = null;
}