What must I do to make my methods awaitable?

Question

How can I roll my own async awaitable methods?

I see that writing an async method is easy as pie in some cases:

private async Task TestGeo()
{
    Geolocator geo = new Geolocator();
    Geoposition pos = await geo.GetGeopositionAsync();
    double dLat = pos.Coordinate.Latitude;
    double dLong = pos.Coordinate.Latitude;
}

...but sadly also see that not just any method can be made async willy-nilly, though; to wit: this doesn't work:

private async Task TestAsyncAwait()
{
    int i = await TaSLs_Classes.TASLsUtils.GetZoomSettingForDistance(5);
}

...it stops me with the compile error, "Cannot await int"; a hint at design time similarly tells me, "type 'int' is not awaitable"

I also tried this with the same results:

    Task<int> i = await TaSLs_Classes.TASLsUtils.GetZoomSettingForDistance(5);

What must I do to make my methods awaitable?

UPDATE

As Linebacker and S. Cleary indicated (any relation to that cat who used to be on KNBR?), this works:

int i = await Task.Run(() => TaSLs_Classes.TASLsUtils.GetZoomSettingForDistance(5));

...that is to say, it compiles -- but it never "moves."

At runtime, it tells me I should "await" the CALL to TestAsyncAwait(), but if I do that, it doesn't compile at all...

`int i = await Task.Run(() => TaSLs_Classes.TASLsUtils.GetZoomSettingForDistance(5));` — L.B, Nov 22 '12 at 19:12
I recommend you read [TAP](http://www.microsoft.com/en-us/download/details.aspx?id=19957) — Christian, Nov 22 '12 at 19:17
So Lambdas are not just de rigeur, but obligatory now? I've viewed them, at least up to now, as clever-clever tricks. — B. Clay Shannon-B. Crow Raven, Nov 22 '12 at 22:17
No, I'm just experimenting - I want to know how to make methods awaitable so that I can "do it until the cows come home" or "without even thinking (much) about it" when I need to. — B. Clay Shannon-B. Crow Raven, Nov 23 '12 at 15:27

score 28 · Accepted Answer · answered Nov 22 '12 at 19:53

You only need to return an awaitable. Task/Task<TResult> is a common choice; Tasks can be created using Task.Run (to execute code on a background thread) or TaskCompletionSource<T> (to wrap an asynchronous event).

Read the Task-Based Asynchronous Pattern for more information.

Jeson Martajaya · Answer 2 · 2020-08-31T22:07:54.110

Your method

private async Task TestAsyncAwait()
{
    int i = await TaSLs_Classes.TASLsUtils.GetZoomSettingForDistance(5);
}

should be written like this

private async Task TestAsyncAwait()
{
    Task<int> t = new Task<int>(() =>
    {
        return TaSLs_Classes.TASLsUtils.GetZoomSettingForDistance(5);
    });
    t.Start();
    await t;
}

If you need to return the int, replace the Task type:

private async Task<int> TestAsyncAwait()
{
    Task<int> t = new Task<int>(() =>
    {
        return TaSLs_Classes.TASLsUtils.GetZoomSettingForDistance(5);
    });
    t.Start();
    return await t;
}

score 3 · Answer 3 · answered Mar 11 '14 at 21:43

3

var something = Task<int>.Factory.StartNew(() => 0);
something.Wait();
int number = something.Result;

answered Mar 11 '14 at 21:43

p3n

79
5

2

Downvoted because the OP is clearly trying to do this asynchronously – aaronburro Aug 01 '16 at 16:42
4

Thanks to aaronburro for adding a downvote explanation. This is too rare. – philologon Nov 22 '16 at 22:30
Rare and useful. – Marcelo Scofano Diniz Nov 09 '21 at 17:23

score 1 · Answer 4 · edited Nov 24 '12 at 00:10

1

You need to either consume the awaited return or return Task<Type of await call>

private async Task<Geoposition> TestGeo()
{
    Geolocator geo = new Geolocator();
    return await geo.GetGeopositionAsync();
}

private async Task<int> TestAsyncAwait()
{
    return await TaSLs_Classes.TASLsUtils.GetZoomSettingForDistance(5);
}

edited Nov 24 '12 at 00:10

svick

236,525
50
385
514

answered Nov 22 '12 at 20:42

Mayank

8,777
4
35
60

The question is about #2, and for #2, the error says "Type 'int' is not awaitable" – Jeson Martajaya Jun 04 '15 at 17:12

What must I do to make my methods awaitable?

UPDATE

4 Answers4