Task Extension to Cater App Wide Service Calls

Question

I am working in xamarin and trying to consume all services using one method. For that I wrote a TaskExtension. So that from every page in the app I can call that extension method. This is to disable the buttons, show loading screen, response handling and to cater exception handling from one point. I am attaching my code below. Need your expert opinions on this solution

Here is my Extension Class

public static class TaskExtensions
{
    public static async Task<ResultViewModel<U>> ExecuteAsyncOperation<U>(this Task<HttpResponseMessage> operation, object sender = null)
    {
        ResultViewModel<U> resultModel = new ResultViewModel<U>();
        Button button = BeforeAsyncCall(sender);
        try
        {
            await BackgroundOperation(operation, resultModel);
        }
        catch (Exception ex)
        {
            resultModel.Status = HttpStatusCode.InternalServerError;
            resultModel.Errors = new List<string>() { "Some error occurred. Please try again." };
        }
        finally
        {
            AfterAsyncCall(button);

        }
        return resultModel;
    }
    static async Task BackgroundOperation<U>(Task<HttpResponseMessage> operation, ResultViewModel<U> resultModel)
    {
        HttpResponseMessage RawResult = await operation;
        var Response = await RawResult.Content.ReadAsStringAsync();
        resultModel.Status = RawResult.StatusCode;
        if (RawResult.IsSuccessStatusCode)
        {
            var responseObj = await Task.Run(() => JsonConvert.DeserializeObject<U>(Response));
            resultModel.Result = responseObj;
        }
        else
        {
            var responseErrorObj = await Task.Run(() => JsonConvert.DeserializeObject<ErrorModel>(Response));
            resultModel.Errors = new List<string>();
            foreach (var modelState in responseErrorObj.ModelState)
            {
                foreach (var error in modelState.Value)
                {
                    resultModel.Errors.Add(error.ToString());
                }
            }
        }
    }
    static Button BeforeAsyncCall(object sender)
    {
        Button button = null;
        if (sender != null)
            button = (Button)sender;
        if (button != null)
            button.IsEnabled = false;
        UserDialogs.Instance.ShowLoading("Loading", MaskType.Black);
        return button;
    }
    static void AfterAsyncCall(Button button)
    {
        UserDialogs.Instance.HideLoading();
        if (button != null)
            button.IsEnabled = true;
    }
}

Here is the Call to my Extension Method

ResultViewModel<TokenModel> response = await new Service(Settings.BaseUrl).Login(loginModel).ExecuteAsyncOperation<TokenModel>(sender);

ResultViewModel

public class ResultViewModel<T> 
    {
        public HttpStatusCode Status { get; set; }
        public T Result { get; set; }
        public List<string> Errors { get; set; }
    }

Async Method

public async Task<HttpResponseMessage> Login(LoginViewModel loginModel)
        {
            try
            {

                var dataList = new List<KeyValuePair<string, string>>();
                dataList.Add(new KeyValuePair<string, string>("grant_type", "password"));
                dataList.Add(new KeyValuePair<string, string>("username", loginModel.Email));
                dataList.Add(new KeyValuePair<string, string>("password", loginModel.Password));
                var request = new HttpRequestMessage()
                {
                    RequestUri = new Uri(this.BaseUrl + "token"),
                    Method = HttpMethod.Post,
                    Content = new FormUrlEncodedContent(dataList)
                };
                var authenticateResponse = await Client.SendAsync(request);
                return authenticateResponse;
            }
            catch (Exception ex)
            {
                return null;
            }
        }

My questions is

1) Is this a good approach?

2) Can we improve it in terms of performance?

3) Am I using Async correctly?

Answer 1

1) Is this a good approach?

There is nothing wrong with this approach.

2) Can we improve it in terms of performance?

There shouldn't be any performance issues with using an extension method, but you can measure to be 100% certain. You are creating a boxing and unboxing situation with the object to button casting. Could you just use Button. Use ViewElement if you want to support multiple element types. Also, There are penalties for using async await, but they are minimal and necessary to not block the UI. You can increase performance by removing the need to recapture the context by adding .ConfigureAwait(false) to your tasks, but in your case you need context to re-enable the button. The use of dynamic seems unnecessary and does have some overhead.

3) Am I using Async correctly?

You don't have to await a Task if the method just returns a Task. You can await it from the calling method. This will reduce overhead on the compiler, and may increase performance. I haven't tested this out before though.

Extension

public static async Task<ResultViewModel<T>> ExecuteAsyncOperation<T>(this Task<HttpResponseMessage> operation, Button button)
{
    ResultViewModel<T> resultModel = new ResultViewModel<T>();
    try
    {
        if (button != null)
            button.IsEnabled = false;
        HttpResponseMessage RawResult = await operation;
        string Response = await RawResult.Content.ReadAsStringAsync();
        resultModel.Status = RawResult.StatusCode;

        if (RawResult.IsSuccessStatusCode)
        {
            var responseObj = JsonConvert.DeserializeObject<T>(Response);
            resultModel.Result = responseObj;
        }
        else
        {
            //create an error model instead of using dynamic I am guessing modelstate here
            List<ModelState> responseObj = JsonConvert.DeserializeObject<List<ModelState>>(Response);
            resultModel.Errors = new List<string>();
            foreach (ModelState modelState in responseObj)
            {
                foreach (var error in modelState.Errors)
                {
                    resultModel.Errors.Add(error.ToString());
                }
            }
        }
    }
    catch (Exception ex)
    {
        resultModel.Status = HttpStatusCode.InternalServerError;
        resultModel.Errors = new List<string>() { "Some error occurred. Please try again." };
    }
    finally
    {
        if (button != null)
            button.IsEnabled = true;
    }
    return resultModel;
}

Calling

var button = sender as Button; 
if (button != null)
{
    ResultViewModel<TokenModel> response = await new Service(Settings.BaseUrl).Login(loginModel).ExecuteAsyncOperation<TokenModel>(sender);
}

Request

public Task<HttpResponseMessage> Login(LoginViewModel loginModel)
{
    var dataList = new List<KeyValuePair<string, string>>();
    dataList.Add(new KeyValuePair<string, string>("grant_type", "password"));
    dataList.Add(new KeyValuePair<string, string>("username", loginModel.Email));
    dataList.Add(new KeyValuePair<string, string>("password", loginModel.Password));
    var request = new HttpRequestMessage()
    {
        RequestUri = new Uri(this.BaseUrl + "token"),
        Method = HttpMethod.Post,
        Content = new FormUrlEncodedContent(dataList)
    };
    return Client.SendAsync(request);
}