改性剂异步不适用于这个项目 [英] The modifier async is not valid for this item

问题描述

这不会出现被数百其它问题，具有相同的错误的副本。我已经看过所有这些，都发现他们是无关的。的

我想提出一个小纸条的应用程序，我试图从目录中读取文件。继MSDN的例子，我有以下的code，但它给我的错误：

I am making a little note app and am trying to read files from a directory. Following the MSDN example, I have the following code, but it is giving me an Error of:

错误1修改异步并不适用于该   项目C：\用户\ Jase \文档\ Visual Studio中   2012 \项目\ AppNameHere \ AppNameHere \的DataModel \ AppNameHereDataSource.cs 192 9 AppNameHere

Error 1 The modifier 'async' is not valid for this item C:\Users\Jase\documents\visual studio 2012\Projects\AppNameHere\AppNameHere\DataModel\AppNameHereDataSource.cs 192 9 AppNameHere

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在code我拥有的是：

---

The code I have is:

    async public NotesDataSource()
    {
        StorageFolder documentsFolder = KnownFolders.DocumentsLibrary;
        StringBuilder outputText = new StringBuilder();

        IReadOnlyList<StorageFile> fileList =
            await documentsFolder.GetFilesAsync();
        outputText.AppendLine("Files:");

        foreach (StorageFile file in fileList)
        {
            if (file.FileType == "txt")
            {
                outputText.Append(file.Name + "\n");
            }
        }
        // lots of irrelevant code removed.
    }

---

我不明白是怎么回事。我也跟着一切一个T。可有人请帮助？

---

I don't understand what's going on here. I followed everything to a "T". Can somebody please help?

感谢您！

推荐答案

您的方法签名不正确。看看它：

Your method signature is incorrect. Look at it:

async public NotesDataSource()

首先，异步有来的在的访问修饰符IIRC。

Firstly, async has to come after the access modifier IIRC.

其次，无论你想创建一个异步的构造方法（你不能这样做），或者你想要写一个方法没有返回类型（这同样是无效的）。

Secondly, either you're trying to create an async constructor (which you can't do) or you're trying to write a method without a return type (which is equally invalid).

试试这个：

public async Task NotesDataSource()

这就是，如果你的意思是这是一个方法。如果你想的有效的创建一个异步的构造函数（或接近它），你必须使用一个异步静态方法：

That's if you meant it to be a method. If you want to effectively create an async constructor (or something close to it) you'd have to use an async static method:

public static async Task<NotesDataSource> CreateInstance()
{
    // Do async stuff here which fetches all the necessary data...

    return new NotesDataSource(...);
}

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