孤立存储文件的困难

Question

I'm building a Windows Phone 7 app in Silverlight. I'm having difficulty using IsolatedStorageFile .

The following method is supposed to write some data to a file:

    private static void writeToFile(IList<Story> stories)
    {
        IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication();
        using (IsolatedStorageFileStream stream = storage.OpenFile(STORIES_FILE, FileMode.Append))
        {
            using (StreamWriter writer = new StreamWriter(stream))
            {
                StringBuilder toJson = new StringBuilder();

                IList<StoryJson> storyJsons = (from story in stories
                                               where !storageStories.Contains(story)
                                               select story.ToStoryJson()).ToList();

                writer.Write(JsonConvert.SerializeObject(storyJsons));
            }

        }

#if DEBUG
            StreamReader reader = new StreamReader(storage.OpenFile(STORIES_FILE, FileMode.Open));
            string contents = reader.ReadToEnd();
#endif
        }

The DEBUG at the end is for me to check that the data is actually being written. I have verified that it is. This method is called 6+ times. Each time, more data is appended.

However, when I go to read the data, the only JSON I get back is that which I wrote in one call of writeToFile() . Here is my method to read:

    private static IList<Story> storageStories;
    private static IList<Story> readFromStorage()
    {
        if (storageStories != null)
        {
            return storageStories;
        }

        IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication();

        if (! storage.FileExists(STORIES_FILE))
        {
            storage.CreateFile(STORIES_FILE);
            storageStories = new List<Story>();
            return storageStories;
        }

        string contents;
        using (IsolatedStorageFileStream stream = storage.OpenFile(STORIES_FILE, FileMode.OpenOrCreate))
        {
            using (StreamReader reader = new StreamReader(stream))
            {
                contents = reader.ReadToEnd();
            }
        }

        JsonSerializer serializer = new JsonSerializer();
        storageStories = JArray.Parse(contents).Select(storyData => storyOfJson(serializer, storyData)).ToList();
        return storageStories;
    }

What could I be doing wrong here? Am I writing to the file incorrectly? I'm pretty sure that the only data that is able to be read back is from the first write.

Update : I added two Flush() calls, but it crashes:

  private static void writeToFile(IList<Story> stories)
        {
            IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication();
            using (IsolatedStorageFileStream stream = storage.OpenFile(STORIES_FILE, FileMode.Append))
            {
                using (StreamWriter writer = new StreamWriter(stream))
                {
                    StringBuilder toJson = new StringBuilder();

                    IList<StoryJson> storyJsons = (from story in stories
                                                   where !storageStories.Contains(story)
                                                   select story.ToStoryJson()).ToList();

                    writer.Write(JsonConvert.SerializeObject(storyJsons));
                    writer.Flush();
                }
                // FAILS
                // "Cannot access a closed file." {System.ObjectDisposedException}

                stream.Flush();
            }
        }

If I comment out the stream.Flush() but leave writer.Flush() , I have the same problem.

Update 2 : I added some print statements. Looks like everything is getting serialized:

Serializing for VID 43
Serializing for VID 17
Serializing for VID 6
Serializing for VID 33
Serializing for VID 4
Serializing for VID 5
Serializing for VID 3

But only the first set is actually being read back:

Deserializing stories with vid: 43

I have run the test a few more times. I'm pretty sure that only the first item is ever being read back.

Answer 1

At first glance it sounds like your stream data is not being flushed to disk.

You are probably thinking that the using block will perform a flush when it Disposes the stream. However I have found that is not always the case and sometimes it is best to force a Flush() at the end.

I remember recently in a codebase that we received from a Microsoft team to port to WP7 that they were forcing a Flush . I questioned it initially, thinking that the Dispose should handle that, however as it was working and we were on a short deadline I did not investigate it further.

Give it go, see what happens... :)

Answer 2

Have you tried explicitly calling

writer.Close()

rather than relying on writer.Dispose()