Proper Error handling

Exoskeletor

greetings guys. im building an android application and i have some second thoughts on some error handling case. I have a method that gets data from the internet by calling this method:

public static string StoredDatesList
{
get => Preferences.Get(nameof(StoredDatesList), string.Empty);
set => Preferences.Set(nameof(StoredDatesList), value);
}
public static async Task GetDraws(Uri url, string date)
{
Dictionary StoredDates = new Dictionary();
StoredDates = JsonConvert.DeserializeObject>(StoredDatesList);
var contents = string.Empty;
HttpClient client = new HttpClient();

        if (StoredDates != null)
            if (StoredDates.ContainsKey(date))
            {
                contents = StoredDates\[date\];
            }
            else
            {
                var current = Connectivity.NetworkAccess;
                if (current != NetworkAccess.Internet)
                    return null;
                client = new HttpClient();
                contents = await client.GetStringAsync(url);
                var res2 = JsonConvert.DeserializeObject(contents.ToString());
                if (180 == res2.content.Count)
                {
                    StoredDates.Add(date, contents);
                    StoredDatesList = JsonConvert.SerializeObject(StoredDates, Formatting.Indented);
                }
            }
        else
        {
            StoredDates = new Dictionary();

            contents = await client.GetStringAsync(url);
            var res2 = JsonConvert.DeserializeObject(contents.ToString());
            if (180 == res2.content.Count)
            {
                StoredDates.Add(date, contents);
                StoredDatesList = JsonConvert.SerializeObject(StoredDates, Formatting.Indented);
            }
        }
        return contents;
    }

the if statement

current != NetworkAccess.Internet)

checks if internet is available, when internet is not available i return null and i check if the data is null and im displaying a message(error, internet is not available etc). I find this approach very bad and im trying to think how is the proper way to handle this. i cannot show a message t

Lost User

If your app can continue without the data, and the user can do nothing about it, there is no point in telling them. It's called: graceful degradation.

It was only in wine that he laid down no limit for himself, but he did not allow himself to be confused by it. ― Confucian Analects: Rules of Confucius about his food

Exoskeletor

No, i meant that not all the times data is needed. When it does, it will throw an error if you dont have

GuyThiebaut

Slightly off topic perhaps, but you are repeating the same block of code twice and could refactor all of this into a single function and just call that function twice:

            contents = await client.GetStringAsync(url);
            var res2 = JsonConvert.DeserializeObject(contents.ToString());
            if (180 == res2.content.Count)
            {
                StoredDates.Add(date, contents);
                StoredDatesList = JsonConvert.SerializeObject(StoredDates, Formatting.Indented);
            }

“That which can be asserted without evidence, can be dismissed without evidence.”

― Christopher Hitchens

Exoskeletor

Oh thank you. Any improvement is highly welcome, i have refactor it to:

public static string StoredDatesList
{
get => Preferences.Get(nameof(StoredDatesList), string.Empty);
set => Preferences.Set(nameof(StoredDatesList), value);
}
public static async Task GetDraws(Uri url, string date)
{
var StoredDates = JsonConvert.DeserializeObject>(StoredDatesList);
var contents = string.Empty;
var current = Connectivity.NetworkAccess;
var client = new HttpClient();

        if (StoredDates != null)
            if (StoredDates.ContainsKey(date))
            {
                contents = StoredDates\[date\];
            }
            else
            {
                if (current != NetworkAccess.Internet)
                    return Helpers.Settings.Common\_Error\_NoInternetConnection;

                contents = await DownloadResults(url, date, StoredDates, contents, client);
            }
        else
        {
            if (current != NetworkAccess.Internet)
                return Helpers.Settings.Common\_Error\_NoInternetConnection;

            StoredDates = new Dictionary();
            contents = await DownloadResults(url, date, StoredDates, contents, client);
        }
        return contents;
    }

    private static async Task DownloadResults(Uri url, string date, Dictionary StoredDates, string contents, HttpClient client)
    {
        contents = await client.GetStringAsync(url);
        var res2 = JsonConvert.DeserializeObject(contents.ToString());
        if (180 == res2.content.Count)
        {
            StoredDates.Add(date, contents);
            StoredDatesList = JsonConvert.SerializeObject(StoredDates, Formatting.Indented);
        }

        return contents;
    }

...
public const string Common_Error_NoInternetConnection = "Error_NoInternetConnection";

So i would check every time if the return sting is equal to Common_Error_NoInternetConnection, Does this sounds like a solid idea?