c# - 如何在 ASP.NET Core 中对 void 方法使用异步/等待？

Question

我正试图进入异步的话题。我想让我的方法之一异步，因为它需要一段时间才能完成，所以我尝试了这个:

public static async Task GenerateExcelFile(HashSet<string> codes, ContestViewModel model)
{
    var totalCodeToDistribute = model.NbrTotalCodes - (model.NbrCodesToPrinter + model.NbrCodesToClientService);
    if (model.NbrTotalCodes > 0)
    {
        using (var package = new ExcelPackage())
        {
                         
            await DoStuff(some, variables, here);
                        
            package.SaveAs(fileInfo);
        }
    }
}

所以我可以在我的 Controller 中这样调用它:

 await FilesGenerationUtils.GenerateExcelFile(uniqueCodesHashSet, model);

但是当涉及到“await”关键字时，它说“Type void is not awaitable”

这是一种等待 void 方法的方法还是不是最佳实践？如果是这样，最好的方法是什么？

Controller :

[HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Index(ContestViewModel model)
        {
            var contentRootPath = _hostingEnvironment.ContentRootPath;

            DirectoryUtils.OutputDir = new DirectoryInfo(contentRootPath + Path.DirectorySeparatorChar
                                                                         + "_CodesUniques" + Path.DirectorySeparatorChar
                                                                         + model.ProjectName +
                                                                         Path.DirectorySeparatorChar
                                                                         + "_Codes");
            var directory = DirectoryUtils.OutputDir;

            var selectedAnswer = model.SelectedAnswer;

            var uniqueCodesHashSet = new HashSet<string>();

            try
            {
                
                while (uniqueCodesHashSet.Count < model.NbrTotalCodes)
                {
                    var generatedString = RandomStringsUtils.Generate(model.AllowedChars, model.UniqueCodeLength);
                    uniqueCodesHashSet.Add(generatedString.ToUpper());
                }

                #region FOR TXT FILES

                if (selectedAnswer == FileExtension.TXT.GetStringValue())
                {
                   await FilesGenerationUtils.GenerateTxtFiles(uniqueCodesHashSet, model, directory);
                }

                #endregion

                #region FOR XLSX FILES

                if (selectedAnswer == FileExtension.XLSX.GetStringValue())
                {
                    await FilesGenerationUtils.GenerateExcelFile(uniqueCodesHashSet, model);
                }

                #endregion
             
       
                return View();
            }
            catch (Exception ex)
            {
                Console.Write(ex);
            }

            return View();
        }

如果我理解你们所说的，我必须创建一个可等待的方法。如果我选择这样的东西，我走对了吗:

public static Task DoStuff(ExcelWorksheet sheet, HashSet<string> codes, int rowIndex, int count, int maxRowValue)
        {
            foreach (var code in codes)
            {
                sheet.Row(rowIndex);
                sheet.Cells[rowIndex, 1].Value = code;
                rowIndex++;
                count++;
                if (rowIndex == maxRowValue && count < (codes.Count - 1))
                {
                    sheet.InsertColumn(1, 1);
                    rowIndex = 1;
                }
            }
            //What should be returned?!
            return null;
        }

Answer 1

您可以编写 async void 方法，但不能等待这些方法:

public static class Program
{
    public static async Task Main()
    {
        const int mainDelayInMs = 500;
        AsyncVoidMethod();
        await Task.Delay(mainDelayInMs);
        Console.WriteLine($"end of {nameof(Main)}");
    }

    static async void AsyncVoidMethod()
    {
        await Task.Delay(1000);
        Console.WriteLine($"end of {nameof(AsyncVoidMethod)}");
    }
}

如您所见，AsyncVoidMethod 是异步的，但我无法编写 await AsyncVoidMethod();。

不应该(大多数时候)使用异步无效方法，因为您不能等待任务完成，并且抛出的任何异常都可能无法处理(因此它可能使您的应用程序崩溃):Why exactly is void async bad?