C#- 在任务异步调用上返回 IEnumerable<object>

Posted 2023-02-19

【中文标题】C#- 在任务异步调用上返回 IEnumerable<object>

【英文标题】：C#- return IEnumerable<object> on task async call

【发布时间】：2019-08-17 04:45:00

【问题描述】：

我有以下代码：

public class TardiisServiceAsync

    private static TardiisServiceAsync instance;

    public static TardiisServiceAsync Instance
    
        //Singleton
        get
        
            if (instance == null)
            
                instance = new TardiisServiceAsync();
            
            return instance;
        
    
    public const string CACHE_PREFIX_TARDIIS_SERVICE = "TardiisServiceAsync_";
    public static Dictionary<string, Tuple<string, object>> clients = new Dictionary<string, Tuple<string, object>>();
    public delegate Task<IEnumerable<object>> GetServiceList(object client, string connectionId, TardiisServiceParameters parameters = null);


    public async Task<IEnumerable<object>> GetDemographicGroupsDelegateAsync(object client, string connectionId, TardiisServiceParameters parameters = null)
    
        //Returns IEnumerable<object> task
        var test = Convert(client.GetType().GetMethod("GetDemographicGroupsAsync").Invoke(client, new object[]  connectionId ));
        var result = await test;
        return (IEnumerable<object>)result;
    

    public async Task<IdNameObject[]> GetDemographicGroupsAsync()
    
        //This task is called from hight level class
        Task<IdNameObject[]> cacheValue = null;
        string cacheKey = CACHE_PREFIX_TARDIIS_SERVICE + Membership.GetUser().UserName + "GetDemographicGroupsAsync" + GetMarketCode();

        if (ConfigurationManager.AppSettings[ConstantsHelper.FIELD_CONFIG_USE_CACHE_KEY] != null && bool.Parse(ConfigurationManager.AppSettings[ConstantsHelper.FIELD_CONFIG_USE_CACHE_KEY]))
        
            if (HttpContext.Current.Cache[cacheKey] == null)
            
                var taskResult = InitializeTardiisInstanceAndCallService(GetDemographicGroupsDelegateAsync);
                var test = await taskResult;
                cacheValue = (Task<IdNameObject[]>)HttpContext.Current.Cache[cacheKey];//This is not implemented yet
             
        

        return await cacheValue;
    

    public static Task<T> Convert<T>(T value)
    
        return Task.FromResult<T>(value);
    

    public static EnumHelper.EnumMarketCode GetMarketCode(EnumHelper.EnumMarketCode? marketCode = null)
    
        //Returns market code
        if (!marketCode.HasValue)
            return (EnumHelper.EnumMarketCode.US);
        else
            return marketCode.Value;
    

    private Task<IEnumerable<object>> InitializeTardiisInstanceAndCallService(GetServiceList getServiceList, TardiisServiceParameters parameters = null, EnumHelper.EnumMarketCode? marketCode = null, bool creatingConnectionsForAllCountries = false, string username = "")
    
        //Get the instance and call the tardiis correct tardiis service depends on the market code
        marketCode = GetMarketCode(marketCode);
        MembershipUser membershipUser = Membership.GetUser();
        string currentUsername = (membershipUser != null ? membershipUser.UserName : username);
        string currentKey = currentUsername + "_" + marketCode;

        if (clients.ContainsKey(currentKey))
        
            try
            
                //check if the connection is still active, or we should reconnect.
                return getServiceList(clients[currentKey].Item2, clients[currentKey].Item1, parameters);
            
            catch (Exception)  
        
        //At this point there is no connection, we need to open it.                            
        object client = TardiisServiceFactory.GetService(marketCode.Value);

        UserDTO userDTO = UserService.Instance.GetByUsername(currentUsername);
        TardiisUserDTO tardiisUserDTO = UserService.Instance.GetTardiisUserByUserIdAndMarketCode(userDTO.ID, marketCode.Value.ToString());

        if (tardiisUserDTO.TardiisUsername == null)
        
            if (creatingConnectionsForAllCountries)
                return null;
            else
                throw new TardiisLoginException("Please enter your credentials");
        

        object user = TardiisServiceFactory.GetUser(marketCode.Value, tardiisUserDTO.TardiisUsername, tardiisUserDTO.TardiisPassword);
        string connectionId;
        try
        
            connectionId = (string)client.GetType().GetMethod("InitConnection").Invoke(client, new object[]  user );
        
        catch (FaultException ex)
        
            // This exception is catched globally by BaseController and prompts the user to enter his
            // tardiis credentials again
            throw new TardiisLoginException(ex.InnerException.Message, ex);
        
        catch (TargetInvocationException ex)
        
            // This exception is catched globally by BaseController and prompts the user to enter his
            // tardiis credentials again
            throw new TardiisLoginException(ex.InnerException.Message, ex);
        

        clients[currentKey] = new Tuple<string, object>(connectionId, client);
        return getServiceList(clients[currentKey].Item2, clients[currentKey].Item1, parameters);
    

    private void AddToCache(string key, object value)
    
        HttpContext.Current.Cache.Add(key, value, null, DateTime.Now.AddMinutes(30), Cache.NoSlidingExpiration, CacheItemPriority.Normal, null);
    

我收到以下错误消息：

无法将“System.Threading.Tasks.Task[System.Object]”类型的对象转换为“System.Collections.Generic.IEnumerable1[System.Object]”类型。

任务的结果是TypedClass[]。

如何在调用方法上以Task<IEnumerable<object>> 的形式返回。

这是另一个具有相似逻辑但以同步方式的类的“副本”。这个想法是改变一些方法 所以它们可以同步运行。

谢谢！

【问题讨论】：

var taskResult = task.Result;当您添加 .result 时，这不是一项任务，它将是您使用的可枚举或其他类型

嗨@Pliskin，感谢您的回复，我明白这一点，但我无法将Task<MyCustomClass> 结果转换为Task<IEnumerable<object>>。谢谢。

taskResult的类型和convert方法的param类型是什么？

结果是Task<TardiisPlanning.TardiisPlanningService.DemographicGroup[]>一个自定义类数组。下面我留下 Convert 方法的代码：public static Task<T> Convert<T>(T value) return Task.FromResult<T>(value);

检查更新的代码，让我知道它是否有效，或者将其添加为 Convert resultado.ToList() 的参数

【参考方案1】：

    public async Task<IEnumerable<object>> GetDemographicGroupsDelegateAsync(object client, string connectionId, TardiisServiceParameters parameters = null)


    var test = Convert(client.GetType().GetMethod("GetDemographicGroupsAsync").Invoke(client, new object[]  connectionId ));
    var result = await test;
    var resultado = test.Result;
    return Convert(new List<Object>resultado);

【参考方案2】：

如果您有 IEnumerable<A> 之类的数组，您可以使用 Linq-Methode Cast<object>() 将其转换为 IEnumerable<object>

public async Task<IEnumerable<object>> GetDemographicGroupsDelegateAsync(object client, string connectionId, TardiisServiceParameters parameters = null)


    var test = Convert(client.GetType().GetMethod("GetDemographicGroupsAsync").Invoke(client, new object[]  connectionId ));
    var task = await test;
    var taskResult = await task;
    return taskResult.Cast<object>();

【讨论】：

嗨，Ackdari，谢谢，但变量 taskResullt 是一个对象类型，不是 awatiable，我说的对吗？

@MarceloArias 好吧，我不知道你的对象是什么类型的？如果您告诉我test 的类型和task 的类型是什么，我可能会澄清我的答案。