var generalExceptionPolicy=Policy.Handle<Exception>().WaitAndRetry(2, retryAttempt =>
                    TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)),(exception,timespan)=>{

        if(attempt++ == 2)
        {
            Toast.MakeText(Activity,"No Connection Bro",ToastLength.Short).Show();


        }
    });
   var test = await generalExceptionPolicy.ExecuteAsync(()=>PostPreLogin (view.FindViewById<EditText> (Resource.Id.mobileTextBox).Text));

public  async Task<string> PostPreLogin(string userName)
    {
        var preloginvalue = await Account.PreLoginPost (userName);
        return preloginvalue;

    }

generalExceptionPolicy.ExecuteAndCapture(() => DoSomething());

async Task<HttpResponseMessage> QueryCurrencyServiceWithRetryPolicy(Func<Task<HttpResponseMessage>> action)
    {
        int numberOfTimesToRetry = 7;
        int retryMultiple = 2;

        //Handle HttpRequestException when it occures
        var response = await Policy.Handle<HttpRequestException>(ex =>
        {
            Debug.WriteLine("Request failed due to connectivity issues.");
            return true;
        })

        //wait for a given number of seconds which increases after each retry
        .WaitAndRetryAsync(numberOfTimesToRetry, retryCount => TimeSpan.FromSeconds(retryCount * retryMultiple))

        //After the retry, Execute the appropriate set of instructions
        .ExecuteAsync(async () => await action());

        //Return the response message gotten from the http client call.
        return response;
    }

var response = await QueryCurrencyServiceWithRetryPolicy(() => _httpClient.GetAsync(ALL_CURRENCIES_URL));