请问怎么得到listbox下的textblock的text？代码如下

请教如何得到listbox下的textblock的text？代码如下
<ListBox Name="listBox1" SelectionChanged="listBox1_SelectionChanged"
  ItemsSource="{Binding Source={StaticResource weatherCollection},Path=DataCollection}">
  <ListBox.ItemTemplate>
  <DataTemplate>
  <Grid >
  <Grid.ColumnDefinitions>
  <ColumnDefinition/>
  <ColumnDefinition/>
  <ColumnDefinition/>
  </Grid.ColumnDefinitions>
  <Grid Grid.Column="0">
  <Image Source="../cellpic.png"/>
  </Grid>
  <Grid Grid.Column="1">
  <TextBlock Name="tb1" Text="XXXXXXXX" Margin="35,25,0,0"/>
  </Grid>
  <Grid Grid.Column="2" >
  <Image Source="../pointer.png" HorizontalAlignment="Right"/>
  </Grid>
   


  </Grid>
  </DataTemplate>
  </ListBox.ItemTemplate>
  </ListBox>

------解决方案--------------------
可参考一下下面的帖子：http://topic.csdn.net/u/20110915/17/d725257a-dfef-44ff-a98d-d4c7125cc995.html
------解决方案--------------------
可参考下该帖子：http://topic.csdn.net/u/20110915/17/d725257a-dfef-44ff-a98d-d4c7125cc995.html