Issue getting NullReferenceException using Http with jwt Xamarin Forms Android - http

Question

So my code works in PostMan querying the api to populate a listview locally in my Android app. But when I run it from within the app, I get NullReferenceException on the line "Items.Clear() in ShipViewModel.cs
I tried hardcoding the address rather than using my APIQueriable path, I tried generating new JWT, and I tried manually cleaning my /bin /obj folders to rule out code not compiling correctly.
ShipsViewModel.cs Xamarin.Forms/ViewModels
{
private GallogClient _gallogClient;
public ObservableCollection<ShipCatalog> Items { get; set; }
public Command LoadItemsCommand { get; }
public ShipsViewModel()
{
Title = "Ships";
_gallogClient = new GallogClient("eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJodHRwOlwvXC9hcGkuZ2FsbG9nLmNvIiwiYXVkIjoiaHR0cDpcL1wvYXBpLmdhbGxvZy5jbyIsImlhdCI6MTM1Njk5OTUyNCwibmJmIjoxMzU3MDAwMDAwLCJkYXRhIjp7ImlkIjo1NywidXNlcm5hbWUiOiJQYXJhIiwiaGFuZGxlIjoiUGFyYSIsImVtYWlsIjoicGFyYWJvbGE5NDlAZ21haWwuY29tIn19.bRpI9hVy-Spky5pbZhJCkyN-MT9RA6ap_yD9ezRxCxo");
LoadItemsCommand = new Command(async () => await ExecuteLoadItemsCommand(), () => !IsBusy);
}
async Task ExecuteLoadItemsCommand()
{
if (IsBusy)
return;
IsBusy = true;
try
{
LoadItemsCommand.ChangeCanExecute();
Items.Clear();
var items = await _gallogClient.GetItemsAsync<ShipList>();
foreach (var item in items.ships.ToList())
{
Items.Add(item);
}
}
catch (Exception ex)
{
Debug.WriteLine(ex);
}
finally
{
IsBusy = false;
}
}
}
}
GallogClient.cs Gallog.API
{
internal readonly HttpClient Client = new HttpClient { BaseAddress = new Uri("https://api.gallog.co/api/") };
public string Jwt { get; set; }
public GallogClient()
{
}
public GallogClient(string jwt)
{
Jwt = jwt;
}
private StringContent JwtContent
{
get {
return new StringContent(JsonConvert.SerializeObject(new
{
jwt = Jwt
}), Encoding.UTF8, "application/json");
}
}
//...
public async Task<T> GetItemAsync<T>(string name) where T : ApiQueryable
{
return await PostAsync<T>($"{GetPath<T>()}/{name}");
}
public async Task<T> GetItemsAsync<T>() where T : ApiQueryable
{
return await PostAsync<T>($"{GetPath<T>()}");
}
internal string GetPath<T>()
{
if (typeof(T).GetCustomAttributes(
typeof(ApiPathAttribute), true
).FirstOrDefault() is ApiPathAttribute at)
{
return at.Path;
}
return null;
}
public async Task<T> PostAsync<T>(string path) where T : ApiQueryable
{
var response = await Client.PostAsync(path, JwtContent);
return JsonConvert.DeserializeObject<T>(await response.Content.ReadAsStringAsync());
}
public async Task<T> PostAsync<T>(object body, string path) where T : ApiQueryable
{
var response = await Client.PostAsync(path,
new StringContent(JsonConvert.SerializeObject(body), Encoding.UTF8, "application/json"));
return JsonConvert.DeserializeObject<T>(await response.Content.ReadAsStringAsync());
}
}
}
ShipList.cs Xamarin.Forms/Models
{
[ApiPath("ships")]
public class ShipList : ApiQueryable
{
public ShipCatalog[] ships { get; set; }
}
public class ShipCatalog
{
public int id { get; set; }
public string name { get; set; }
// ...etc etc
}
}

Answer 1

Items is null because you declared it but have never initialized it
public ShipsViewModel()
{
...
Items = new ObservableCollection<ShipCatalog>();
...
}