C# - 索引超出了数组的边界,在for循环中使用相同的列表大小

Question

我正在.NET中创建一个文件下载器,它使用异步任务从服务器下载文件数组.但是,即使我创建Task[]并返回string[]相同的长度.

这是我的方法:

    public static string[] DownloadList(string[] urlArray, string[] toPathArray, string login = "", string pass = "", bool getExt = false)
    {
        Console.WriteLine("DownloadList({0}, {1}, {2}, {3}, {4})", urlArray, toPathArray, login, pass, getExt);
        try {
            returnedArray = new string[urlArray.Length];
            Task[] taskArray = new Task[urlArray.Length];
            for (int i = 0; i < urlArray.Length; i++)
            {
                Thread.Sleep(1000);
                Console.WriteLine("i = {0}", i);
                Task task = new Task(() => { returnedArray[i] = Download(urlArray[i], toPathArray[i], login, pass, getExt, true); });
                task.Start();
                taskArray[i] = task;
            }
            Task.WaitAll(taskArray);
            Thread.Sleep(1000);
            Console.WriteLine();
            Console.WriteLine("Done! Press Enter to close.");
            Console.ReadLine();
            return returnedArray;
        }
        catch(Exception e)
        {
            Console.WriteLine();
            Console.WriteLine(e.Message);
            Console.ReadLine();
            return null;
        }
    }

和例外:

这指向这一行:

我知道这会让我错过一些愚蠢的东西,但是我正在喋喋不休地试图解决它.我在这里先向您的帮助表示感谢!

Answer 1

它看起来像访问修改关闭问题.复制i到本地变量:

for (int i = 0; i < urlArray.Length; i++)
{
    int index = i;
    Thread.Sleep(1000);
    Console.WriteLine("i = {0}", index );
    Task task = new Task(() => { returnedArray[index] = Download(urlArray[index], toPathArray[index], login, pass, getExt, true); });
    task.Start();
    taskArray[index] = task;
}