错误 CS0029：无法将类型“字符串”隐式转换为“System.Threading.Tasks.Task”<string> '</string>

Question

I get this error message in the last line of OnPlayFabError method:

return output;

Error CS0029: Cannot implicitly convert type 'string' to 'System.Threading.Tasks.Task'

What is wrong with the line return output;? I want to get the value of the variable "output" in this line:

error = errormessage.Result;

What is wrong with my code?

MainClass.cs:

string Countryname = string.Empty;
string Cityname = string.Empty;
string Errormessage = string.Empty;
var GotNames = await Extensionmethods.GetPlayerCountryData(PlayerPlayFabID, "Country", "City");
Countryname = GotNames.countryname;
Cityname = GotNames.cityname;
Errormessage = GotNames.error;

Extensionmethods.cs:

public static class Extensionmethods
{
    public static async Task<(string error, string countryname, string cityname)> GetPlayerCountryData(this string playerplayfabid, string country, string city)
    {
        string error = string.Empty;
        string countryname = string.Empty;
        string cityname = string.Empty;

        var resultprofile = await PlayFabClientAPI.GetUserDataAsync(new PlayFab.ClientModels.GetUserDataRequest()
        {
            PlayFabId = playerplayfabid,
            Keys = null
        });

        if (resultprofile.Error != null)
        {
            // Handle error if any
            var errormessage = OnPlayFabError(resultprofile.Error);
            error = errormessage.Result;
        }
        else
        {
            if (resultprofile.Result.Data == null || !resultprofile.Result.Data.ContainsKey(country) || !resultprofile.Result.Data.ContainsKey(city))
                Console.WriteLine("No Country/City");
            else
            {
                countryname = resultprofile.Result.Data[country].Value;
                cityname = resultprofile.Result.Data[city].Value;
            }
        }

        return (error, countryname, cityname);
    }

    public static Task<string> OnPlayFabError(this PlayFabError obj)
    {
        string output = string.Empty;
        switch (obj.Error)
        {
            case PlayFabErrorCode.AccountBanned:
                output = "Account is banned." + "Hier die geladenen Daten aus der Textdatei anzeigen.";
            break;
            case PlayFabErrorCode.EmailAddressNotAvailable:
                output = "E-mail address is already in use. Please choose another e-mail address.";
            break;
            case PlayFabErrorCode.InvalidParams:
                output = "Please fill out all the text fields.";
            break;
            case PlayFabErrorCode.InvalidUsernameOrPassword:
                output = "Wrong username or password.";
            break;
            case PlayFabErrorCode.UsernameNotAvailable:
                output = "Username not available. Please choose another username.";
            break;
            case PlayFabErrorCode.ConnectionError:
                output = "Connection error. Please check your network connection.";
            break;
            default:
                output = "Unknown error!";
            break;
        }

        return output;
    }
}

Answer 1

A method returning a task should almost always be an asynchronous method. If the method isn't async, then just return the type you want, no need to wrap it in a task.

That being said, all you need to do is change the return type of your OnPlayFabErrorAsync to string OnPlayFabErrorAsync(..) instead of Task<string> OnPlayFabErrorAsync(..) . So this is your new method:

public static string OnPlayFabError(this PlayFabError obj)
{
    // ...
}

Answer 2

A good rule of thumb is that if your function returns a Task , then the function name should end with Async . This then reminds you that you need to await that function.

OnPlayFabError(this PlayFabError obj) becomes OnPlayFabErrorAsync(this PlayFabError obj) which then reminds you to await it:

var errormessage = await OnPlayFabErrorAsync(resultprofile.Error);

In your case, there is no need for OnPlayFabError to be async (because it currently does no I/O), so it might be easier to just make it return a string instead of a Task<string> .