C# 等待/异步引用错误
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Await/async reference error
提问by csharp newbie
im trying to do some async operation in some function returning string.
我试图在一些返回字符串的函数中做一些异步操作。
async private void button1_Click(object sender, EventArgs e)
{
string output = await thr_calc(this, null);
}
async private Task<string> thr_calc(object sender, EventArgs e)
{
return await zzztest();
}
string zzztest()
{
string asd;
//some stuff here
return asd;
}
But it gives me errors on each string contains words async/await! Im using russian version of ms vs express 2012 for windows desktop, so here is the translation of errors:
但是它给我的每个字符串都包含错误，包含单词 async/await！我在 Windows 桌面上使用俄语版的 ms vs express 2012，所以这里是错误的翻译：
Cannot find all types required by the 'async' modifier. Are you targeting the wrong framework version, or missing a reference to an assembly?
找不到“async”修饰符所需的所有类型。您的目标是错误的框架版本，还是缺少对程序集的引用？
And 2 errors:
和 2 个错误：
Predefined type 'System.Runtime.CompilerServices.IAsyncStateMachine' is not defined or imported
未定义或导入预定义类型“System.Runtime.CompilerServices.IAsyncStateMachine”
I cant find that reference. I've tried to use async/await before and it worked fine, now im doing all the same and its not. What I am missing?
我找不到那个参考。我之前尝试过使用 async/await 并且它工作得很好，现在我做的都是一样的，但不是。我缺少什么？
采纳答案by redtuna
In thr_calc, use:
return zzztest()Also, make sure you've set your project to use .Net 4.5 or later (that's when "async" was introduced)
在 thr_calc 中，使用：
return zzztest()此外，请确保您已将项目设置为使用 .Net 4.5 或更高版本（即引入“异步”时）
回答by chue x
If zzztestis a long running operation, you can do this to run it in a background thread:
如果zzztest是长时间运行的操作，您可以这样做以在后台线程中运行它：
async private Task<string> thr_calc(object sender, EventArgs e)
{
return await Task.Run<string>(() => zzztest());
}
The above should solve your compile errors as well.
以上内容也应该可以解决您的编译错误。
If zzztestis NOT a long running operation, then consider NOT using await/ async.
如果zzztest不是长时间运行的操作，则考虑不使用await/ async。
回答by Robin
On a .NET 4.0 project, I resolved 'Predefined type 'System.Runtime.CompilerServices.IAsyncStateMachine' is not defined or imported' by installing the Microsoft.Bcl.Async package from nuget. In VS's nuget package manager, search for 'bcl' and install the async-looking one.
在 .NET 4.0 项目中，我通过从 nuget 安装 Microsoft.Bcl.Async 包解决了“未定义或导入预定义类型‘System.Runtime.CompilerServices.IAsyncStateMachine’”。在 VS 的 nuget 包管理器中，搜索“bcl”并安装看起来像异步的那个。
