RichTextBoxDemo

效果：

<Window x:Class="RichTextBoxDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:RichTextBoxDemo"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid >
            <RichTextBox   VerticalScrollBarVisibility="Auto" HorizontalScrollBarVisibility="Auto" TextChanged="LogTextChanged" >
                <FlowDocument>
                    <Paragraph x:Name="myParagraph" />
                </FlowDocument>
            </RichTextBox>
        </Grid>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace RichTextBoxDemo
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            WriteLog(new Run() { Text = "黑色" });
            WriteLog(new Run() { Foreground = Brushes.Red, Text = "红色" });
            WriteLog(new Run() { Foreground = Brushes.Green, Text = "绿色" ,FontSize = 20});
            WriteLog(new Run() { Foreground = Brushes.Blue, Text = "蓝色", FontSize = 40, FontWeight = FontWeights.Bold });
        }

        #region 打印日志方法
        private void WriteLog(Run var)
        {
            myParagraph.Dispatcher.Invoke(new Action(() =>
            {
                myParagraph.Inlines.Add(var);
                myParagraph.Inlines.Add(new LineBreak());//换行（如果用
也能换行，但是要把内容拷贝到Word里面
换行符不能识别，推荐使用LineBreak()来换行）
            }));
        }

        #endregion
        private void LogTextChanged(object sender, TextChangedEventArgs e)
        {
            RichTextBox richTextBox = sender as RichTextBox;
            richTextBox.ScrollToEnd();
        }
    }
}