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[duplicate]

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Thread parameters being changed 2 answers

线程参数被更改2个答案

I am creating a file downloader in .NET which downloads an array of files from a server using Asynchronous tasks. However, even though I create the Task[] and returned string[] with the same length.

我在.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,即使我创建了Task []并返回了具有相同长度的string []。

Here is my method:

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;
        }
    }

and the exception:

和例外:

which points to this line:

这指向这一行:

I know it will be something daft that I missed, but I'm rattling my brain trying to figure it out. Thanks for the help in advance!

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!

3 个解决方案

#1

It looks like Access to Modified Closure problem. Copy i to local variable:

它看起来像访问Modified Closure问题。将i复制到局部变量:

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;
}

#2

@Backs's answer is correct. Interestingly, in recent versions of .Net, if you use foreach, then the loop variable is closed over. So, you could:

@Backs的回答是正确的。有趣的是,在.Net的最新版本中,如果使用foreach,则循环变量将被关闭。所以,你可以:

foreach(var i in Enumerable.Range(0, urlArray.Length))
{
    ... new Task(() => { returnedArray[i] = ...
}

without needing to take a copy.

无需复制。

#3

-1

Looks like you are overshootinhg the array by one, because you count the length of the array in the cycle, and that's 10, while the array goes from 0 to 9.

看起来你的数字超过了一个,因为你计算周期中数组的长度,那是10,而数组从0到9。

 for (int i = 0; i < urlArray.Length; i++)

Should be

 for (int i = 0; i < urlArray.Length - 1; i++)

#1