How to get value returned from async Task<string> function(); in C#

Question

I have an async method and I want to get a message from the same method when it gets done.

Below is the code

 static async Task<string> pizza()
        {
            await Task.Delay(10);
            for (int i = 0; i < 100; i++)
            {
                //Console.WriteLine("Processing pizza...");
            }
            return "Pizza is ready";

        }

And I want to get receive this message at calling point

....... code 
Task t=null;
            switch (option)
            {
                case 1:
                    {

                        await Task.Run(() =>
                        {

                         t=pizza();// asynchronous method  

                        });
                        Console.WriteLine(t.ToString());
                    }
                    break;
 .... other code

any reason why you accepted a wrong answer, when a correct one is available from the beginning? — Panagiotis Kanavos
– Panagiotis Kanavos, Commented May 23, 2017 at 7:56

Austin Winstanley · Accepted Answer · 2017-05-23 06:09:48Z

8

Do you need the Task.Run part? You can await of you are inside an async method:

var result = await pizza();

Console.WriteLine(result);

You can also call result:

var result = pizza().Result;

answered May 23, 2017 at 6:09

Austin Winstanley

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3 Comments

Iqra. Over a year ago

Would it run asynchronously? As I have run multiple articles but I am not getting when to use Task.run or when to use await task.

Panagiotis Kanavos Over a year ago

@Eqra there is no ambiguity. Task.Run runs something in the background. await only awaits for the result of an asynchronous operation. Your method already returns a Task

Iqra. Over a year ago

:( Alright. I try to understand, though I am trying this since days!

Tvde1 · Accepted Answer · 2017-05-23 10:11:22Z

5

You can either

var pizza = await pizza();

Or

var pizza = pizza().GetAwaiter().GetResult();

answered May 23, 2017 at 10:11

Tvde1

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3 Comments

Iqra. Over a year ago

I have done using something like this Console.WriteLine(await Task.Run(() => pizza()));

Tvde1 Over a year ago

That looks complicated and isn't neccecary.

VMAtm Over a year ago

GetAwaiter is internal method and shouldn't be called

Rohit Garg · Accepted Answer · 2017-05-23 07:24:35Z

-1

You can use:

var returnValue = string.Empty;
    {
        returnValue = await Pizza();
    }
    Console.WriteLine(returnValue);

It will still behave asynchronously. When await statement is encountered, control will return to main thread and execution will not be paused. After a while when Pizza method has returned executing, state machine will automatically execute the returnValue output

You don't need to use Task.Run just for awaiting. You just need to await the async method. Then later on you can use returnValue wherever you want to.

edited May 23, 2017 at 7:24

answered May 23, 2017 at 6:09

Rohit Garg

4932 silver badges12 bronze badges

8 Comments

Panagiotis Kanavos Over a year ago

No, that's what await is for. .Result will block until the task returns which is a bad idea unless you are absolutely certain that the task has already finished

Iqra. Over a year ago

But It won't remain asynchronous then. I want to do it Asynchronously.

Rohit Garg Over a year ago

@PanagiotisKanavos I didn't say that t.Result needs to be awaited. I meant that t.Result can be used after awaiting the method. In that way awaited method still behaves asynchronously and we get our result when it is finished executing.

Panagiotis Kanavos Over a year ago

Then you don't need .Result at all. Just use what await returned. BTW, your code won't compile because t is NOT a task. It's the result of the Task, ie a string

Rohit Garg Over a year ago

@Eqra Check the edited answer. It is more elaborated now. Code will execute asynchronously. That is what async/await do. I just meant that after await, you can access t.result which is asynchronous way of retrieving values from async methods. But definitely you need to await first and then use t.Result.

|

Liquid Core · Accepted Answer · 2017-05-23 06:58:47Z

-4

If you await it, it will be executed asynchronously. If you do t.Result it will be executed synchronously.

It really depends on your needs to execute it sync or async.

Here we go with the supposed expert programmers downvote rush.

Try to remove await, put .Result and you will get this:

"This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread."

edited May 23, 2017 at 6:58

answered May 23, 2017 at 6:43

Liquid Core

1

4 Comments

Iqra. Over a year ago

I want to do it asynchronously but want a final message too when my asynchronous method will complete its processing.

Panagiotis Kanavos Over a year ago

@Eqra that's what await is for

Panagiotis Kanavos Over a year ago

.Result won't execute anything synchronously. The task will still run asynchronously. The calling thread though will block until the tast returns

Jon Skeet Over a year ago

Indeed, calling .Result doesn't change how the task executes at all (unless the task's execution needs to execute more code on the calling thread, of course, causing deadlock). It changes how the code calling .Result behaves.

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