控制台应用程序 async/await 不返回我的列表

Question

Why doesn't the following compile? I'm just trying to get a simple list to return.

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var list = MainAsync(args).Wait();
            //Compile error: Cannot assign void to an implicitly-typed variable
        }

        static async Task MainAsync(string[] args)
        {
            Bootstrapper bs = new Bootstrapper();
            var list = await bs.GetList();
        }
    }

    public class Bootstrapper
    {
        public async Task<List<string>> GetList()
        {
            List<string> toReturn = new List<string>();
            toReturn.Add("hello");
            toReturn.Add("world");
            return await toReturn;
            //Compile error: 'List<string>' does not contain a definition for 'GetAwaiter' and no extension method 'GetAwaiter' accepting a first argument of type 'List<string>'
        }
    }
}

Answer 1

There is no use case here to make this method async , just return a List<string>

public List<string> GetList()
{
    List<string> toReturn = new List<string>();
    toReturn.Add("hello");
    toReturn.Add("world");
    return toReturn;
}

However, if there were some IO or otherwise async calls you needed to make in GetList , then you could do the following

public async Task<List<string>> GetList()
{
    // now we have a reason to be async (barely)
    await Task.Delay(1000);
    List<string> toReturn = new List<string>();
    toReturn.Add("hello");
    toReturn.Add("world");
    return toReturn;
}

Update

or another way to simulate an async workload is Task.FromResult

private async Task<List<string>> Test()
{
    List<string> toReturn = new List<string>();
    toReturn.Add("hello");
    toReturn.Add("world");
    return await Task.FromResult(toReturn);
}

Update

As mentioned by Sir Rufo, there is a lot to this async and await a good place to start is with Stephen Cleary , he is a very well articulated blogger on such topics