CODEWITHSUNDEEP
c#iosasynchronousxamarinxamarin.ios
pankaj
pankaj

Reputation: 8338

GetStringAsync method call hangs the UI and never completes

I am trying to access my url using GetStringAsync method but the call hangs and never ends. When I check it in browser it works perfect but somehow in my code it never ends. My code:

public bool Login(string url,string userName, string password)
    {
        try
        {
            Task<LoginResponse> response = GetLoginData(url, userName, password);
            if(response.Result.UserInfo.UserId > 0){
                IsAuthenticated = true;
            }
            return IsAuthenticated;
        }
        catch (ArgumentException argex)
        {
            ErrorMessage = argex.Message;
            IsAuthenticated = false;
            return IsAuthenticated;
        }
    }

    public async Task<LoginResponse> GetLoginData(string url, string userName, string password)
    {
        try{
            var param = new AuthenticationParam();
            param.UserName = userName;
            param.Password = password;

            var response = await LoginValidate(url, param);

            response = response.Replace("\"", string.Empty);
            response = response.Replace("\\", "\"");

            LoginResponse list = JsonConvert.DeserializeObject<LoginResponse>(
                response, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore });

            return list;
        }
        catch(Exception e){
            System.Diagnostics.Debug.WriteLine(e);
            return new LoginResponse();
        }
    }

    private static async Task<string> LoginValidate(string url, AuthenticationParam param){
        try
        {
            string result = "";
            using (var client = new HttpClient())
            {
                var json_data = string.Empty;
                json_data = JsonConvert.SerializeObject(param);
                var byteArray = Encoding.UTF8.GetBytes(json_data);
                var base64 = Convert.ToBase64String(byteArray);
                url = $"{url}{base64}";
                result = await client.GetStringAsync(url);
                return result;
            }
        }
        catch (Exception ex)
        {
            return "Error: " + ex.Message;
        }
    }

It hangs at line result = await client.GetStringAsync(url);

Upvotes: 2

Views: 684

Answers (1)

Peter Bons
Peter Bons

Reputation: 29730

if(response.Result.UserInfo.UserId > 0){ -> .Result is a blocking call and can lead to deadlocks. Use await all the way up the call chain.

public async Task<bool> Login(string url,string userName, string password)
{
    try
    {
        var response = await GetLoginData(url, userName, password);
        if(response.UserInfo.UserId > 0){
            IsAuthenticated = true;
        }
        return IsAuthenticated;
    }
    catch (ArgumentException argex)
    {
        ErrorMessage = argex.Message;
        IsAuthenticated = false;
        return IsAuthenticated;
    }
}

Up in the call stack use var success = await Login(...);

And please, read this excellent blogpost for the background about how this deadlock is created.

Upvotes: 7

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