How to return from async Task method?

JeffinAtl 161

My method is async Task like following.

public async Task MyMethod()
{
    string[] lists = GetCustomerLists();

    foreach (string lst in lists)
    {
        // do somethong
        // if meet some condition to return
        ????
    }
}

What is the correct way to return from the method among the followings?

break;
return;
await Task.CompletedTask;

P a u l 10,406 Reputation points

2022-05-02T15:10:58.747+00:00

Do you ever call await anywhere in your method?
JeffinAtl 161 Reputation points

2022-05-02T16:38:46.747+00:00

Calling await in the method
P a u l 10,406 Reputation points

2022-05-02T16:45:17.267+00:00

If you're calling await somewhere in the method and the method returns a Task (i.e. void returning task/no return value) then you don't explicitly need to return anything.

If you were returning a Task<T> then your async method does return a value so you will need to return it with a return statement.

So in your case if you are calling await and MyMethod just needs to communicate success/error to the calling method then you don't need to specify anything.
Jack J Jun 24,286 Reputation points Microsoft Vendor

2022-05-03T06:19:37.997+00:00

@JeffinAtl , Welcome to Microsoft Q&A, what value do you want to return or just return the task type? Please refer to the Microsoft doc Async return types (C#) to choose the method you wanted to use it in your async Task method.

Accepted answer

Jamie Hayashi 121

I'm using break(); on this example.

Karen Payne MVP 35,036

I would not use break, here is a better path.

using System.Collections.Generic;
using System.Threading.Tasks;

namespace AsyncSimple.Classes
{
    public class Operations
    {
        public delegate void OnIterate(Customer customer);
        public static event OnIterate IterateEvent;
        public static async Task<List<Customer>> GetCustomerLists()
        {
            await Task.Delay(0);

            return new List<Customer>();
        }

        public static async Task<bool> Work()
        {
            var customerLists = await GetCustomerLists();

            foreach (var customer in customerLists)
            {
                if (customer.HasDiscount)
                {
                    IterateEvent?.Invoke(customer);
                    // do something here
                    return false;
                }
            }

            return true;
        }
    }

    public class Customer
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public bool HasDiscount { get; set; }
        public int Discount { get; set; }
    }
}

Nikriaz 1 Reputation point

2023-03-17T13:36:24.0433333+00:00

break in this example will exit from foreach and not from the method

2 additional answers

Bruce (SqlWork.com) 55,686 Reputation points

2022-05-02T16:38:46.42+00:00

just return or break if you want fall though to the end of the method.

because it is an async method, the compiler will convert the return/exit to a return task.
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Karen Payne MVP 35,036

Here is an abstract example where all Customers from a specific country are returned in a class named CustomerOperations.

This it's Entity Framework but that doesn't matter, the same applies for other read operations. Think of context.Customers as string[] lists = GetCustomerLists();

public static async Task<List<Customers>> ByCountry(int countryIdentifier)
{
    return await Task.Run(async () =>
    {
        await using var context = new NorthwindContext();
        return await context.Customers
            .Where(customer => customer.CountryIdentifier == countryIdentifier)
            .Select(customer => customer)
            .ToListAsync();
    });
}

Usage

public static async Task Demo()
{
    int identifier = 12;
    var customers = await CustomerOperations.ByCountry(identifier);
}