silverlight隔离存储

cs代码如下：

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;
using System.IO.IsolatedStorage;
using System.IO;
namespace gelicunchu
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private void click1(object sender,RoutedEventArgs e)
        {
            
            using(IsolatedStorageFile store=IsolatedStorageFile.GetUserStoreForApplication()){
                Int64 newspace = 20971520;
                 Int64 curspace=store.AvailableFreeSpace;
                if(curspace<newspace){
                    if(!store.IncreaseQuotaTo(newspace)){
                        ChildWindow child = new System.Windows.Controls.ChildWindow();
                        child.Title = "用户不准许扩展空间";
                        child.Content = "请求失败。。。。。。。";
                        child.Show();
                    }
                }
                using (StreamWriter sw = new StreamWriter(store.OpenFile("a.txt",FileMode.OpenorCreate,FileAccess.Write)))
                {
                    sw.WriteLine(textBox1.Text);
                }
            }
        }

        private void click2(object sender,RoutedEventArgs e)
        {
            using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication())
            {
                using (StreamReader sr = new StreamReader(store.OpenFile("a.txt",FileAccess.Read)))
                {
                    textBlock1.Text = sr.ReadLine();
                }
            }
        }
    }
}
xaml文件:

xaml文件：

<Grid x:Name="LayoutRoot" Background="White">
        <Button Content="写入" Height="23" Click="click1"  HorizontalAlignment="Left" Margin="10,10,0" Name="button1" VerticalAlignment="Top" Width="75" />
        <Button Content="读取" Height="23" Click="click2" HorizontalAlignment="Left" Margin="10,43,0" Name="button2" VerticalAlignment="Top" Width="75" />
        <TextBox Height="23" HorizontalAlignment="Left" Margin="10,76,0" Name="textBox1" VerticalAlignment="Top" Width="120" />
        <TextBlock Height="23" HorizontalAlignment="Left" Margin="20,105,0" Name="textBlock1" Text="TextBlock" VerticalAlignment="Top" />
    </Grid>