为什么paragraph设置了ToolTip，但是把鼠标移动到段落上，ToolTip却没有显示？

Question

            Run rr = new Run("mmmmm");
            rr.Background = Brushes.Green;
            rr.Foreground = Brushes.Red;            Paragraph pp = new Paragraph();
            pp.ToolTip = "aaa";
            pp.Inlines.Add(rr);            this.richTextBox2.Document.Blocks.Add(pp);

Answer 1

前台xaml代码：<Window x:Class="Test.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow">
    <Grid>
        <RichTextBox name="richTextBox2"></RichTextBox>
    </Grid></Window>后台xaml.cs代码：
[code=C#]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
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 Test
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            Run rr = new Run("mmmmm");
            rr.Background = Brushes.Green;
            rr.Foreground = Brushes.Red;            Paragraph pp = new Paragraph();
            pp.ToolTip = "aaa";
            pp.Inlines.Add(rr);            this.richTextBox2.Document.Blocks.Add(pp);
        }
     }
} [/code]

Answer 2

前台xaml代码：<Window x:Class="Test.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow">
    <Grid>
        <RichTextBox name="richTextBox2"></RichTextBox>
    </Grid></Window>
后台xaml.cs代码：using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
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 Test
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            Run rr = new Run("mmmmm");
            rr.Background = Brushes.Green;
            rr.Foreground = Brushes.Red;            Paragraph pp = new Paragraph();
            pp.ToolTip = "aaa";
            pp.Inlines.Add(rr);            this.richTextBox2.Document.Blocks.Add(pp);
        }
     }
}