异步任务和任务之间有什么区别 [英] What is the difference between async Task and Task

问题描述

例如，这段代码有什么区别:

For example, what is the difference between this code:

public async Task DoSomething(int aqq)
{
    await DoAnotherThingAsync(aqq);
}

和这个:

public Task DoSomething(int aqq)
{
    DoAnotherThingAsync(aqq);
}

它们都正确吗?

推荐答案

如果使用正确，两个签名都是正确的.

Both signatures are correct, if used properly.

async Task允许您在方法内部使用await关键字.第一个例子完全可以.

async Task allows you to use await keyword inside your method. The first example is totally OK.

第二个示例缺少return语句:

The second example missing return statement:

public Task DoSomething(int aqq)
{
   return DoAnotherThingAsync(aqq);
}

使用第二个签名，您不能使用await关键字，但是您仍然可以返回从其他地方获得的某些任务，例如Task.FromResult(true);

Going with second signature you cannot use await keyword, but still you can return some task, that you got from somwhere else, for example, Task.FromResult(true);

为您提供另一个区别，请考虑以下示例:

To give you another difference consider the example:

public async Task DoSomething1(int aqq)
{
    await DoAnotherThingAsync(aqq); //blocks here and wait DoAnotherThingAsync to respond
    SomethingElse();
}


public Task DoSomething2(int aqq)
{
    var task = DoAnotherThingAsync(aqq); //keep going here, not waiting for anything
    SomethingElse();
    return task;
}

public async Task DoAnotherThingAsync(int aqq)
{
    await Task.Delay(100);
}

public void SomethingElse()
{
    //do something
}

如果您使用异步/等待，则实际上是在等待任务完成.返回任务并不等待任务完成.

If you are using async/await you are actually waiting the task to complete. Returning a task doesn't wait for the task to be completed.

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