有人可以向我解释如何返回任务的结果吗?
我目前正在尝试执行以下操作,但我的任务不会返回我期望的列表吗?这里有什么问题?
我目前正在尝试执行以下操作,但我的任务不会返回我期望的列表吗?这里有什么问题?
static void Main() { List<Task> tasks = new List<Task>(); List<string> sha256_hashes = new List<string>(); List<string> results = new List<string>(); sha256_hashes.Add("hash00"); sha256_hashes.Add("hash01"); sha256_hashes.Add("hash03"); foreach(string sha256 in sha256_hashes) { string _sha256 = sha256; var task = Task.Factory.StartNew(() => GetAdditionalInfo(_sha256)); tasks.Add(task); } Task.WaitAll(tasks.ToArray()); //I want to put all the results of each task from tasks but the problem is //I can't use the Result method from the _task because Result method is not available //below is my plan to get all the results: foreach(var _task in tasks) { if(_task.Result.Count >= 1) //got an error Only assignment,call,increment,dec.... results.AddRange(_task.Result); //got an error Only assignment,dec.... } //Do some work about results } static List<string> GetAdditionalInfo(string hash) { //this code returns information about the hash in List of strings }
解决方法
要从Task返回结果,您需要将Task定义为:Task< TResult>并将结果的返回类型作为泛型参数传递. (否则任务将不返回任何内容)
例如:
// Return a value type with a lambda expression Task<int> task1 = Task<int>.Factory.StartNew(() => 1); int i = task1.Result; // Return a named reference type with a multi-line statement lambda. Task<Test> task2 = Task<Test>.Factory.StartNew(() => { string s = ".NET"; double d = 4.0; return new Test { Name = s,Number = d }; }); Test test = task2.Result; // Return an array produced by a PLINQ query Task<string[]> task3 = Task<string[]>.Factory.StartNew(() => { string path = @"C:\Users\Public\Pictures\Sample Pictures\"; string[] files = System.IO.Directory.GetFiles(path); var result = (from file in files.AsParallel() let info = new System.IO.FileInfo(file) where info.Extension == ".jpg" select file).ToArray(); return result; });
问题是您没有指定Task将返回任何内容.
您已经定义了一个不返回任何内容的任务列表.
当您将Task定义为您的List中的List的泛型类型时,您需要做的是在Task中指定返回类型.就像是:
var taskLists = new List<Task<List<string>>>();
这是您为任务指定返回类型的方式
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