刚学windows phone开发，写了个记事本，有有关问题，求高手解答

刚学windows phone开发，写了个记事本，有问题，求高手解答
在page1页面保存文本，返回主页没有显示文本，已经用binding绑定了数据，但是就是不显示，请问怎么办，本人新手，真心搞不懂。望高手能抽空看下，谢谢。
这是主页面
        <Grid x:Name="ContentPanel" Margin="0,124,10,0" Grid.RowSpan="2">
            <ListBox Name="_LB_main" Margin="3.099,2.005,-4.229,437.534" RenderTransformOrigin="0.5,0.5" 
UseLayoutRounding="False" d:LayoutRounding="Auto">
                <ListBox.RenderTransform>
                    <CompositeTransform Rotation="0.232"/>
                </ListBox.RenderTransform>
                <ListBox.ItemTemplate >
                    <DataTemplate >
                            <Grid  HorizontalAlignment="Left" Margin="12,192,0.0">
                                <Grid.RowDefinitions >
                                    <RowDefinition Height="33"/>
                                    <RowDefinition Height="67"/>
                                </Grid.RowDefinitions >
                            <HyperlinkButton Name="_hybtn_1" Content="{Binding titile_tbx1}"  Height="80" Width="461" Click="_hybtn_1_Click"/>
                            <TextBlock  Name="_tb1_1" TextWrapping="Wrap" Text="{Binding body_txb1}" Height="52" Width="461"/>
                            </Grid >
                    </DataTemplate >
                </ListBox.ItemTemplate >
            </ListBox >

这是page1页面
        <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
            <TextBox Name="_tbx_title" HorizontalAlignment="Left" Height="72" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="456" Margin="0,10,0,0"/>
            <TextBox Name="_tbx_body" HorizontalAlignment="Left" Height="641" Margin="0,104,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="456" TextChanged="_tbx_body_TextChanged"/>

        </Grid>
    </Grid>
    <phone:PhoneApplicationPage.ApplicationBar>
        <shell:ApplicationBar IsVisible="True" IsMenuEnabled="True">
            <shell:ApplicationBarIconButton IconUri="appbar.save.rest.png" Text="保存" Click="ApplicationBarIconButton_Click_1"/>
            <shell:ApplicationBarIconButton IconUri="appbar.cancel.rest.png" Text="删除" Click="ApplicationBarIconButton_Click_2"/>
            <shell:ApplicationBar.MenuItems>
            </shell:ApplicationBar.MenuItems>
        </shell:ApplicationBar>
    </phone:PhoneApplicationPage.ApplicationBar>

下面是主页面 mainpage.xaml代码

using System;

using System.Collections.Generic;

using System.Linq;

using System.Net;

using System.Windows;

using System.Windows.Controls;

using System.Windows.Documents;

using System.Windows.Input;

using System.Windows.Media;

using System.Windows.Media.Animation;

using System.Windows.Shapes;