Question

我在用返回类型的泛型方法转换为泛型集合类型时遇到了困难。

在this answer中明确写明是为了避免

打开通用类型

但是在this answer中说明了如何执行此操作。

我承认，我使用泛型来避免为三种不同的返回类型编写相同代码的三倍。现在，编译器告诉我，

并非所有代码路径都返回值

调用者方法调用者示例：

public ObservableCollection<LoadedJockey> Jockeys { get; private set; }

Jockeys = await _updateDataService.UpdateDataAsync(Jockeys, DataUpdateModules.JPlFrom, DataUpdateModules.JPlTo, "updateJockeysPl");

我的通用方法如下：

public async Task<ObservableCollection<T>> UpdateDataAsync<T>(ObservableCollection<T> genericCollection, int idFrom, int idTo, string jobType) where T : IConvertible
        {
            //variables reset here
            _loopCounterProgressBar = 0;
            _idFromProgressBar = idFrom;
            _idToProgressBar = idTo;

            if (typeof(T) == typeof(LoadedHorse))
            {
                //do something here
            }
            else if (typeof(T) == typeof(LoadedJockey))
            {
                //do something here
            }
            else if (typeof(T) == typeof(LoadedHistoricalRace))
            {
                //do something here
            }

            //initial
            SemaphoreSlim throttler = new SemaphoreSlim(_degreeOfParallelism);
            List<Task> tasks = new List<Task>();
            TokenSource = new CancellationTokenSource();
            CancellationToken = TokenSource.Token;
            OnProgressBarTick();

            //run loop
            for (int i = idFrom; i < idTo; i++)
            {
                int id = i;

                tasks.Add(Task.Run(async () =>
                {
                    try
                    {
                        if (CancellationToken.IsCancellationRequested)
                            return;

                        await throttler.WaitAsync(TokenSource.Token);

                        if (jobType.Contains("Horses"))
                        {
                            await //call service method
                        }
                        else if (jobType.Contains("Jockeys"))
                        {
                            await //call service method
                        }
                        else if (jobType.Contains("Historic"))
                        {
                            await //call service method
                        }
                    }
                    catch (Exception e)
                    {

                    }
                    finally
                    {
                        _loopCounterProgressBar++;

                        EventHandler<UpdateBarEventArgs> progressBarTick = _updateProgressEventHandler;

                        OnProgressBarTick();

                        throttler.Release();
                    }
                }));
            }

            try
            {
                await Task.WhenAll(tasks);
            }
            catch (OperationCanceledException)
            {

            }
            finally
            {
                //save results in file when finish

                }
            }
            //here I wanted to return some result depending on T
            if (typeof(T) == typeof(LoadedHorse))
            {
                return (ObservableCollection<T>)Convert.ChangeType(Horses, typeof(ObservableCollection<T>));
            }
            else if (typeof(T) == typeof(LoadedJockey))
            {
                return (ObservableCollection<T>)Convert.ChangeType(Jockeys, typeof(ObservableCollection<T>));
            }
            else if (typeof(T) == typeof(LoadedHistoricalRace))
            {
                return (ObservableCollection<T>)Convert.ChangeType(Races, typeof(ObservableCollection<T>));
            }
        }

如您所见，我希望收到3种不同的 T 。而且我认为我涵盖了所有内容。我的解决方案基于this example。我猜想我可能将Convert的类型错误地写为T，但是我不应该怎么做。

Answer 1

按照 Camilo Terevinto 的建议，我在if else链else { throw new ArgumentException() }的末尾添加了内容，编译器对此感到满意。

如何将ObservableCollection <SomeType>转换回ObservableCollection <T>？

1 个答案: