c# - 使用单例模式时，我的公共(public)类应该返回私有(private)实例还是公共(public)实例？

Question

我有一个这样定义的单例:

public partial class MoonDataManager
{

    static MoonDataManager _singletonInstance;
    public static MoonDataManager SingletonInstance
    {
        get
        {
            return _singletonInstance;
        }
        private set
        {
            _singletonInstance = value;
        }
    }

我有一个安全创建实例的函数:

   public static async Task<MoonDataManager> CreateSingletonAsync()
    {
            _singletonInstance = new MoonDataManager();

我应该:

return  _singletonInstance;  (field) 

或

return SingletonInstance;  (property)

我很关心垃圾回收，尤其是在 Xamarin 中的 iOS 或 Android 中。

此外，如果 C# 中有此的命名模式，请告诉我是否偏离了标准。

---

更新:

现在我想我真的被线程和异步方法困住了。以下是对象及其目标:

• MoonDataManager :运行 RegisterTable<Models.IssuerKey>每 table 一次。这是一个本质上运行 (new MobileServiceSQLiteStore).DefineTable<T>() 的通用方法

• OfflineStore : 这是 MobileServiceSQLiteStore .

• MobileClient : 这是 MobileServiceClient .

• MoonDataManager依赖关系:MoonDataManager 需要OfflineStore 和MobileClient 来完成初始化。具体来说，它执行 MobileServiceClient .SyncContext.InitializeAsync(OfflineStore)

我不确定如何理解这种杂乱无章的依赖关系……或者如何让代码看起来更漂亮，并且是线程安全的。

这是代码的新迭代:

private readonly Lazy<MobileServiceClient> lazyMobileClient = 
        new Lazy<MobileServiceClient>(() => new MobileServiceClient(Constants.ApplicationURL), true); // true for thread safety
    public  MobileServiceClient MobileClient { get { return lazyMobileClient.Value; } }


    private readonly Lazy< MobileServiceSQLiteStore> offlineDB =
        new Lazy<MobileServiceSQLiteStore>(() =>  new MobileServiceSQLiteStore(Constants.OfflineDBName), true ); // true for thread safety
    private MobileServiceSQLiteStore OfflineStore { get { return offlineDB.Value; } }

    private static readonly Lazy<MoonDataManager> lazy =  new Lazy<MoonDataManager>(() => new MoonDataManager(), true); // true for thread safety
    public static MoonDataManager Instance { get { return lazy.Value; } }

    private MoonDataManager()
    {

             MoonDataManager.Instance.RegisterTable<Models.IssuerKey>();

            // Initialize file sync
            // todo: investigate FileSyncTriggerFactory overload. 
            //Was present on Mar 30, 2016 Channel9  https://channel9.msdn.com/events/Build/2016/P408
            MoonDataManager.Instance.MobileClient.InitializeFileSyncContext
                           (new IssuerKeyFileSyncHandler(Instance),   Instance.OfflineStore);

            // NOTE THE ASYNC METHOD HERE (won't compile)
            await MoonDataManager.Instance.MobileClient
                                 .SyncContext.InitializeAsync(MoonDataManager.Instance.OfflineStore,
                                StoreTrackingOptions.NotifyLocalAndServerOperations);

    }

Answer 1

对于 .NET 4 或更高版本，您可以使用 Lazy<T>并像这样创建它。

public sealed class Singleton
{
    private static readonly Lazy<Singleton> lazy =
        new Lazy<Singleton>(() => new Singleton(), true); // true for thread safety

    public static Singleton Instance { get { return lazy.Value; } }

    private Singleton()
    {
    }
}

只有在第一次访问时才会创建它，并且它是线程安全的。