silvetlight ListBox Item项自动填满

 <UserControl.Resources>
        <Style x:Key="ListBoxItemStyle" TargetType="ListBoxItem">
            <Setter Property="HorizontalContentAlignment" Value="Stretch" />
            <Setter Property="HorizontalAlignment" Value="Stretch" />
        </Style>
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" Background="White">
        <Grid Width="500" Height="300">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto" />
                <ColumnDefinition />
            </Grid.ColumnDefinitions>
            <ListBox x:Name="listbox1" Grid.Column="1" ItemContainerStyle="{StaticResource ListBoxItemStyle}">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="Auto" />
                                <ColumnDefinition />
                            </Grid.ColumnDefinitions>
                            <StackPanel>
                                <TextBlock Text="姓名" />
                                <TextBlock Text="年龄" />
                            </StackPanel>
                            <TextBox Grid.Column="1" Text="{Binding Address}" IsReadOnly="True" TextWrapping="Wrap" />
                        </Grid>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>
        </Grid>
    </Grid>