參考文件：

https://stackoverflow.com/questions/15610940/show-linenumbers-from-the-richtextbox-in-wpf

效果：

前臺：

<Grid>
        <Border BorderBrush="Gray"
                BorderThickness="1">
            <ScrollViewer VerticalScrollBarVisibility="Auto"
                          HorizontalScrollBarVisibility
 
="Disabled">

                <DockPanel>
                    <TextBlock x:Name="LineNumberTextBlock"
                               Background="#CFCFCF"
                               Foreground="#008497" />
                    <TextBox x:Name="InfoTbx"  AcceptsReturn="True"
                               BorderThickness
 
="1 0 0 0"
                               VerticalScrollBarVisibility="Disabled"
                               TextChanged="InfoTbx_OnTextChanged">
                    </TextBox>
                </DockPanel> 
            </ScrollViewer>
        </Border>
    </Grid>

後臺：

 public
 
 TextBoxWithLineNumber()
        {
            InitializeComponent();
            InfoTbx.Loaded += delegate
            {
                //當載入後，行號才有效
                InfoTbx_OnTextChanged(InfoTbx, null);
            };
        }

        public string GetInputInfo()
        {
            return InfoTbx.Text;
        }

        public void SetIsReadOnly(bool isReadOnly)
        {
            InfoTbx.IsReadOnly = isReadOnly;
        }

        public void SetTextInfo(string txt)
        {
            InfoTbx.Text = txt;
        }

        private void InfoTbx_OnTextChanged(object sender, TextChangedEventArgs e)
        {
            var textBox = sender as TextBox;
            var x = string.Empty;

            for(var i = 0; i < textBox.LineCount && i < 2000; i++)
            {
                x += i + 1 + "\n";
            }

            LineNumberTextBlock.Text = x;
        }

原始碼：

https://files.cnblogs.com/files/lizhijian/2020-12-23-WPF%E9%87%8CTextBox%E6%98%BE%E7%A4%BA%E8%A1%8C%E5%8F%B7.zip