Using async/await still blocks UI on Xamarin.Android

Question

I'm working on a Xamarin.Android project and the app needs to consume web service before updating the UI. I applied async/await but it still blocks the UI.

Here is the UI code

    private async void Login(object sender, EventArgs e)
    {
        var username = _usernamEditText.Text.Trim();
        var password = _passwordEditText.Text.Trim();
        var progressDialog = ProgressDialog.Show(this, "", "Logging in...");
        var result = await _userService.AuthenticateAsync(username, password);

        progressDialog.Dismiss();
    }

Here is the service code

public async Task<AuthenticationResult> AuthenticateAsync(string username, string password)
    {
        using (var httpClient = CreateHttpClient())
        {
            var url = string.Format("{0}/token", Configuration.ServiceBaseUrl);
            var body = new List<KeyValuePair<string, string>>
            {
                new KeyValuePair<string, string>("username", username),
                new KeyValuePair<string, string>("password", password),
                new KeyValuePair<string, string>("grant_type", "password")
            };
            var response = httpClient.PostAsync(url, new FormUrlEncodedContent(body)).Result;
            var content = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
            var obj = new JSONObject(content);
            var result = new AuthenticationResult {Success = response.IsSuccessStatusCode};

            if (response.IsSuccessStatusCode)
            {
                result.AccessToken = obj.GetString("access_token");
                result.UserName = obj.GetString("userName");
            }
            else
            {
                result.Error = obj.GetString("error");

                if (obj.Has("error_description"))
                {
                    result.ErrorDescription = obj.GetString("error_description");
                }
            }

            return result;
        }
    }

Do I miss anything? Thank you.

It’s usually a bad idea to block on async code by calling Task.Wait or Task.Result. msdn.microsoft.com/en-us/magazine/jj991977.aspx — Jon Douglas
– Jon Douglas, Commented Jul 29, 2016 at 16:55

Mark Larter · Accepted Answer · 2016-07-29 14:21:54Z

9

You're not awaiting PostAsync, you're just taking the Result. This makes the call synchronous.

Change that line to await and it will run asynchronously.

        var response = await httpClient.PostAsync(url, new FormUrlEncodedContent(body));

edited Jul 29, 2016 at 14:21

Mark Larter

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answered Jul 29, 2016 at 13:56

Sami Kuhmonen

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1 Comment

Agile Hobo Over a year ago

Thanks Sami. It fixed the problem.

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