Storing objects in IsolatedStorageSettings

问题

I have an object I want to store in the IsolatedStorageSettings, which I wan't to reuse when the application restarts.

My problem lies in that the code I have written for some reason does not remember the object when trying to access the key upon restarting it.

namespace MyNameSpace
{
    public class WindowsPhoneSettings
    {
        private const string SelectedSiteKey = "SelectedSite";
        private IsolatedStorageSettings isolatedStore = IsolatedStorageSettings.ApplicationSettings;

        private T RetrieveSetting<T>(string settingKey)
        {
            object settingValue;
            if (isolatedStore.TryGetValue(settingKey, out settingValue))
            {
                return (T)settingValue;
            }
            return default(T);
        }

        public bool AddOrUpdateValue(string Key, Object value)
        {
            bool valueChanged = false;

            if (isolatedStore.Contains(Key))
            {
                if (isolatedStore[Key] != value)
                {
                    isolatedStore[Key] = value;
                    valueChanged = true;
                }
            }
            else
            {
                isolatedStore.Add(Key, value);
                valueChanged = true;
            }
            return valueChanged;
        }

        public MobileSiteDataModel SelectedSite
        {
            get
            {
                return RetrieveSetting<MobileSiteDataModel>(SelectedSiteKey);
            }
            set
            {
                AddOrUpdateValue(SelectedSiteKey, value);
                isolatedStore.Save();
            }
        }
    }
}

I then instantiate WindowsPhoneSettings in App.xaml.cs and make a public getter and setter for it. To be able to access it in the whole application. Debugging this shows that the right object gets stored in the isolated store, but when closing the app and reopening it isolated store seems to be empty. I have tried this on both the emulator and a real device. As you can see I do call the save method when setting the object.

What am I doing wrong here?

回答1:

I ended up saving the settings to a file in the isolated storage as IsolatedStorageSettings never seemed to work.

So my code ended up like this:

public class PhoneSettings
{
    private const string SettingsDir = "settingsDir";
    private const string SettingsFile = "settings.xml";

    public void SetSettings(Settings settings)
    {
        SaveSettingToFile<Settings>(SettingsDir, SettingsFile, settings);
    }

    public Settings GetSettings()
    {
        return RetrieveSettingFromFile<Settings>(SettingsDir, SettingsFile);
    }

    private T RetrieveSettingFromFile<T>(string dir, string file) where T : class
    {
        IsolatedStorageFile isolatedFileStore = IsolatedStorageFile.GetUserStoreForApplication();
        if (isolatedFileStore.DirectoryExists(dir))
        {
            try
            {
                using (var stream = new IsolatedStorageFileStream(System.IO.Path.Combine(dir, file), FileMode.Open, isolatedFileStore))
                {
                    return (T)SerializationHelper.DeserializeData<T>(stream);
                }
            }
            catch (Exception ex)
            {
                System.Diagnostics.Debug.WriteLine("Could not retrieve file " + dir + "\\" + file + ". With Exception: " + ex.Message);
            }
        }
        return null;
    }

    private void SaveSettingToFile<T>(string dir, string file, T data)
    {
        IsolatedStorageFile isolatedFileStore = IsolatedStorageFile.GetUserStoreForApplication();
        if (!isolatedFileStore.DirectoryExists(dir))
            isolatedFileStore.CreateDirectory(dir);
        try
        {
            string fn = System.IO.Path.Combine(dir, file);
            if (isolatedFileStore.FileExists(fn)) isolatedFileStore.DeleteFile(fn); //mostly harmless, used because isolatedFileStore is stupid :D

            using (var stream = new IsolatedStorageFileStream(fn, FileMode.CreateNew, FileAccess.ReadWrite, isolatedFileStore))
            {
                SerializationHelper.SerializeData<T>(data, stream);
            }
        }
        catch (Exception ex)
        {
            System.Diagnostics.Debug.WriteLine("Could not save file " + dir + "\\" + file + ". With Exception: " + ex.Message);
        }
    }
}

And a settings class just containing the stuff I want to save. This could be:

class Settings
{
    private string name;
    private int id;

    public string Name
    {
        get { return name; }
        set { name = value; }
    }

    public int Id
    {
        get { return id; }
        set { id = value; }
    }
}

EDIT: Sample of how SerializationHelper could be implemented

public static class SerializationHelper
{
    public static void SerializeData<T>(this T obj, Stream streamObject)
    {
        if (obj == null || streamObject == null)
            return;

        var ser = new DataContractJsonSerializer(typeof(T));
        ser.WriteObject(streamObject, obj);
    }

    public static T DeserializeData<T>(Stream streamObject)
    {
        if (streamObject == null)
            return default(T);

        var ser = new DataContractJsonSerializer(typeof(T));
        return (T)ser.ReadObject(streamObject);
    }
}

回答2:

Objects stored in IsolatedStorageSettings are serialised using the DataContractSerializer and so must be serializable. Ensure they can be or serialize (and deserialize) them yourself before adding to (and after removing from) ISS.

If the items aren't there when trying to retrieve then it may be that they couldn't be added in the first place (due to a serialization issue).

回答3:

Here is the code I use to save an object to isolated storage and to load an object from isolated storage -

private void saveToIsolatedStorage(string keyname, object value)
{
  IsolatedStorageSettings isolatedStore = IsolatedStorageSettings.ApplicationSettings;
  isolatedStore.Remove(keyname);
  isolatedStore.Add(keyname, value);
  isolatedStore.Save();
}

private bool loadObject(string keyname, out object result)
{
  IsolatedStorageSettings isolatedStore = IsolatedStorageSettings.ApplicationSettings;

  result = null;
  try
  {
    result = isolatedStore[keyname];
  }
  catch
  {
    return false;
  }
  return true;
}

Here is code I use to call the above -

private void SaveToIsolatedStorage()
{
  saveToIsolatedStorage("GameData", GameData);
}

private void LoadFromIsolatedStorage()
{
  Object temp;
  if (loadObject("GameData", out temp))
  {
    GameData = (CGameData)temp;
  }
  else
  {
    GameData.Reset();
  }
}

Note that the objects I save and restore like this are small and serializable. If my object contains a 2 dimensional array or some other object which is not serializable then I perform my own serialization and deserialization before using iso storage.

回答4:

What if you changed RetrieveSetting<T> to this:

private T RetrieveSetting<T>(string settingKey)
{
  T settingValue;
  if(isolatedStore.TryGetValue(settingKey, out settingValue))
  {
    return (T)settingValue;
  }
  return default(T);
}

Notice that the object being fetched is being declared as type T instead of object.

来源：https://stackoverflow.com/questions/7415864/storing-objects-in-isolatedstoragesettings