win8 app基础知识(挂起、恢复状态的一些数据操作)

snake_l

　　在Win8 metro应用程序中，当程序挂起的时候，有一些数据需要临时保存起来，以便应用程序恢复到之前的状态
　　下面这个SuspensionManager 类是微软写的demo，作下记录，下次会用到。
　　


class SuspensionManager
{
    static private Dictionary sessionState_ = new Dictionary();
    static private List knownTypes_ = new List();
    private const string filename = "_sessionState.xml";
    // Provides access to the currect session state
    static public Dictionary SessionState
    {
        get { return sessionState_; }
    }
    // Allows custom types to be added to the list of types that can be serialized
    static public List KnownTypes
    {
        get { return knownTypes_; }
    }
    // Save the current session state
    static async public Task SaveAsync()
    {
        // Get the output stream for the SessionState file.
        StorageFile file = await ApplicationData.Current.LocalFolder.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);
        IRandomAccessStream raStream = await file.OpenAsync(FileAccessMode.ReadWrite);
        using (IOutputStream outStream = raStream.GetOutputStreamAt(0))
        {
            // Serialize the Session State.
            DataContractSerializer serializer = new DataContractSerializer(typeof(Dictionary), knownTypes_);
            serializer.WriteObject(outStream.AsStreamForWrite(), sessionState_);
            await outStream.FlushAsync();
        }
    }
    // Restore the saved sesison state
    static async public Task RestoreAsync()
    {
        // Get the input stream for the SessionState file.
        try
        {
            StorageFile file = await ApplicationData.Current.LocalFolder.GetFileAsync(filename);
            if (file == null) return;
            IInputStream inStream = await file.OpenSequentialReadAsync();
            // Deserialize the Session State.
            DataContractSerializer serializer = new DataContractSerializer(typeof(Dictionary), knownTypes_);
            sessionState_ = (Dictionary)serializer.ReadObject(inStream.AsStreamForRead());
        }
        catch (Exception)
        {
            // Restoring state is best-effort.  If it fails, the app will just come up with a new session.
        }
    }