(1)使用 RichTextBox.Document.Selection属性
(2)访问RichTextBox.Document.Blocks属性的“blocks”中的Text
2. 在XAML中增加内容给RichTextBox:
<RichTextBox IsSpellCheckEnabled="True">
   <FlowDocument>
        <Paragraph>
<!-- 这里加上你的内容 -->
          This is a richTextBox. I can <Bold>Bold</Bold>, <Italic>Italicize</Italic>, <Hyperlink>Hyperlink stuff</Hyperlink> right in my document.
        </Paragraph>
   </FlowDocument>
</RichTextBox>
3. 缩短段间距,类似<BR>,而不是<P>
方法是使用Style定义段间距:
    <RichTextBox>
        <RichTextBox.Resources>
          <Style TargetType="{x:Type Paragraph}">
            <Setter Property="Margin" Value="0"/>
          </Style>
        </RichTextBox.Resources>
        <FlowDocument>
          <Paragraph>
            This is my first paragraph... see how there is...
          </Paragraph>
          <Paragraph>
            a no space anymore between it and the second paragraph?
          </Paragraph>
        </FlowDocument>
      </RichTextBox>
4. 从文件中读出纯文本文件后放进RichTextBox或直接将文本放进RichTextBox中:
private void LoadTextFile(RichTextBox richTextBox, string filename)
{
    richTextBox.Document.Blocks.Clear();
    using (StreamReader streamReader = File.OpenText(filename)) {
           Paragraph paragraph = new Paragraph();
           paragraph.Text = streamReader.ReadToEnd();
           richTextBox.Document.Blocks.Add(paragraph);
    }
}

5.如何在RichTextBox中添加文本

}
6. 取得指定RichTextBox的内容：
private string GetText(RichTextBox richTextBox) 
{
        TextRange textRange = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);
        return textRange.Text;
}
7. 将RTF (rich text format)放到RichTextBox中：
        private static void LoadRTF(string rtf, RichTextBox richTextBox)
        {
            if (string.IsNullOrEmpty(rtf)) {
                throw new ArgumentNullException();
            }
            TextRange textRange = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);
            using (MemoryStream rtfMemoryStream = new MemoryStream()) {
                using (StreamWriter rtfStreamWriter = new StreamWriter(rtfMemoryStream)) {
                    rtfStreamWriter.Write(rtf);
                    rtfStreamWriter.Flush();
                    rtfMemoryStream.Seek(0, SeekOrigin.Begin);
                    //Load the MemoryStream into TextRange ranging from start to end of RichTextBox.
                    textRange.Load(rtfMemoryStream, DataFormats.Rtf);
                }
            }
        }
8. 将文件中的内容加载为RichTextBox的内容
        private static void LoadFile(string filename, RichTextBox richTextBox)
        {
            if (string.IsNullOrEmpty(filename)) {
                throw new ArgumentNullException();
            }
            if (!File.Exists(filename)) {
                throw new FileNotFoundException();
            }
            using (FileStream stream = File.OpenRead(filename)) {
                TextRange documentTextRange = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);
                string dataFormat = DataFormats.Text;
                string ext = System.IO.Path.GetExtension(filename);
                if (String.Compare(ext, ".xaml",true) == 0) {
                    dataFormat = DataFormats.Xaml;
                }
                else if (String.Compare(ext, ".rtf", true) == 0) {
                    dataFormat = DataFormats.Rtf;
                }
                documentTextRange.Load(stream, dataFormat);
            }        
        }
9. 将RichTextBox的内容保存为文件：
        private static void SaveFile(string filename, RichTextBox richTextBox)
        {
            if (string.IsNullOrEmpty(filename)) {
                throw new ArgumentNullException();
            }
            using (FileStream stream = File.OpenWrite(filename)) {
                TextRange documentTextRange = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);
                string dataFormat = DataFormats.Text;
                string ext = System.IO.Path.GetExtension(filename);
                if (String.Compare(ext, ".xaml", true) == 0) {
                    dataFormat = DataFormats.Xaml;
                }
                else if (String.Compare(ext, ".rtf", true) == 0) {
                    dataFormat = DataFormats.Rtf;
                }
                documentTextRange.Save(stream, dataFormat);
            }
        }
10. 做个简单的编辑器：
  <!-- Window1.xaml -->
  <DockPanel>
    <Menu DockPanel.Dock="Top">
      <MenuItem Header="_File">
        <MenuItem Header="_Open File" Click="OnOpenFile"/>
        <MenuItem Header="_Save" Click="OnSaveFile"/>
        <Separator/>
        <MenuItem Header="E_xit" Click="OnExit"/>
      </MenuItem>      
    </Menu>
    <RichTextBox Name="richTextBox1"></RichTextBox>     
  </DockPanel>
        // Window1.xaml.cs
        private void OnExit(object sender, EventArgs e) {
            this.Close();
        }
        private void OnOpenFile(object sender, EventArgs e) {
            Microsoft.Win32.OpenFileDialog ofd = new Microsoft.Win32.OpenFileDialog();
            ofd.Filter = "Text Files (*.txt; *.xaml; *.rtf)|*.txt;*.xaml;*.rtf";
            ofd.Multiselect = false;
            if (ofd.ShowDialog() == true) {
                LoadFile(ofd.SafeFileName, richTextBox1);
            }
        }
        private void OnSaveFile(object sender, EventArgs e) {
            Microsoft.Win32.SaveFileDialog sfd = new Microsoft.Win32.SaveFileDialog();
            sfd.Filter = "Text Files (*.txt; *.xaml; *.rtf)|*.txt;*.xaml;*.rtf";
            if (sfd.ShowDialog() == true) {
                SaveFile(sfd.SafeFileName, richTextBox1);
            }
        }

取出richTextBox里面的内容
第一种方法：将richTextBox的内容以字符串的形式取出
string xw = System.Windows.Markup.XamlWriter.Save(richTextBox.Document);
第二种方法：将richTextBox的类容以二进制数据的方法取出
FlowDocument document = richTextBox.Document;
System.IO.Stream s = new System.IO.MemoryStream(); 
System.Windows.Markup.XamlWriter.Save(document, s); 
byte[] data = new byte[s.Length];
s.Position = 0;
s.Read(data, 0, data.Length);
s.Close();

赋值给richTextBox

第一种方法：将字符串转换为数据流赋值给richTextBox中

System.IO.StringReader sr = new System.IO.StringReader(xw);
System.Xml.XmlReader xr = System.Xml.XmlReader.Create(sr);
richTextBox1.Document = (FlowDocument)System.Windows.Markup.XamlReader.Load(xr);
第二种方法：将二进制数据赋值给richTextBox
System.IO.Stream ss = new System.IO.MemoryStream(data);
FlowDocument doc = System.Windows.Markup.XamlReader.Load(ss) as FlowDocument;
ss.Close();
richTextBox1.Document = doc;

清空RichTextBox的方法

System.Windows.Documents.FlowDocument doc = richTextBox.Document;
doc.Blocks.Clear();

如何将一个String类型的字符串赋值给richTextBox
myRTB.Document = new FlowDocument(new Paragraph(new Run(myString))); 
FlowDocument doc = new FlowDocument();
Paragraph p = new Paragraph(); // Paragraph 类似于 html 的 P 标签
Run r = new Run(myString); // Run 是一个 Inline 的标签
p.Inlines.Add(r);
doc.Blocks.Add(p);
myRTB.Document = doc;

如何将richTextBox中的内容以rtf的格式完全取出
string rtf = string.Empty;
TextRange textRange = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);
using (System.IO.MemoryStream ms = new System.IO.MemoryStream())
{
textRange.Save(ms, System.Windows.DataFormats.Rtf);
ms.Seek(0, System.IO.SeekOrigin.Begin);
System.IO.StreamReader sr = new System.IO.StreamReader(ms);
rtf = sr.ReadToEnd();
}

操作RichTextBox

复制 ToolBarCopy.Command = System.Windows.Input.ApplicationCommands.Copy;
剪切 toolBarCut.Command = System.Windows.Input.ApplicationCommands.Cut;
粘贴 ToolBarPaste.Command = System.Windows.Input.ApplicationCommands.Paste;
撤销 ToolBarUndo.Command = System.Windows.Input.ApplicationCommands.Undo;
复原 ToolBarRedo.Command = System.Windows.Input.ApplicationCommands.Redo;
文字居中 toolBarContentCenter.Command = System.Windows.Documents.EditingCommands.AlignCenter;
文字居右 toolBarContentRight.Command = System.Windows.Documents.EditingCommands.AlignRight;
文字居左 toolBarContentLeft.Command = System.Windows.Documents.EditingCommands.AlignLeft;
有序排列 ToolBarNumbering.Command = System.Windows.Documents.EditingCommands.ToggleNumbering;
无序排列 ToolBarBullets.Command = System.Windows.Documents.EditingCommands.ToggleBullets;
字体变大
int fontSize = Convert.ToInt32(richTextBox.Selection.GetPropertyValue(TextElement.FontSizeProperty));
fontSize++;
richTextBox.Selection.ApplyPropertyValue(TextElement.FontSizeProperty, fontSize.ToString());