C#•2y ago

ArgumentNullException when argument is not null

I have this code:

public class Config
{
  [JsonProperty("token")]
  public string Token = "TOKEN HERE";

  [JsonProperty("source_url")]
  public string SourceUrl = "SOURCE URL HERE";

  [JsonProperty("server_url")]
  public string ServerUrl = "SERVER URL HERE";

  [JsonProperty("invite_url")]
  public string InviteUrl = "INVITE URL HERE";

  [JsonIgnore]
  private string _fileName;

  public Config(string fileName)
  {
    _fileName = fileName;

    if (!File.Exists(_fileName)) File.Create(_fileName).Close();

    var loaded = JsonConvert.DeserializeObject<Config>(File.ReadAllText(_fileName));
    if (loaded is not null)
    {
      Token = loaded.Token;
      SourceUrl = loaded.SourceUrl;
      ServerUrl = loaded.ServerUrl;
      InviteUrl = loaded.InviteUrl;
    }
    else
    {
      File.WriteAllText(_fileName, JsonConvert.SerializeObject(new Config(), Formatting.Indented));
    }
  }

  private Config()
  {
    _fileName = string.Empty;
  }

  public void Update()
  {
    File.WriteAllText(_fileName, JsonConvert.SerializeObject(this, Formatting.Indented));
  }
}

public class Config
{
  [JsonProperty("token")]
  public string Token = "TOKEN HERE";

  [JsonProperty("source_url")]
  public string SourceUrl = "SOURCE URL HERE";

  [JsonProperty("server_url")]
  public string ServerUrl = "SERVER URL HERE";

  [JsonProperty("invite_url")]
  public string InviteUrl = "INVITE URL HERE";

  [JsonIgnore]
  private string _fileName;

  public Config(string fileName)
  {
    _fileName = fileName;

    if (!File.Exists(_fileName)) File.Create(_fileName).Close();

    var loaded = JsonConvert.DeserializeObject<Config>(File.ReadAllText(_fileName));
    if (loaded is not null)
    {
      Token = loaded.Token;
      SourceUrl = loaded.SourceUrl;
      ServerUrl = loaded.ServerUrl;
      InviteUrl = loaded.InviteUrl;
    }
    else
    {
      File.WriteAllText(_fileName, JsonConvert.SerializeObject(new Config(), Formatting.Indented));
    }
  }

  private Config()
  {
    _fileName = string.Empty;
  }

  public void Update()
  {
    File.WriteAllText(_fileName, JsonConvert.SerializeObject(this, Formatting.Indented));
  }
}

And whenever I try to access the following field, I get the following exception:

private static Config Config = new("config.json");

private static Config Config = new("config.json");

System.TypeInitializationException: 'The type initializer for 'class' threw an exception.'

Inner Exception:
ArgumentNullException: Path cannot be null. (Parameter 'path')

System.TypeInitializationException: 'The type initializer for 'class' threw an exception.'

Inner Exception:
ArgumentNullException: Path cannot be null. (Parameter 'path')

22 Replies

Anton•2y ago

which line does it get thrown at? in the constructor

Bujju•2y ago

How do I see that?

Anton•2y ago

the debugger should show you try instantiating the config in normal flow, like in the main method, if it doesn't show the line the fact that it's statically initialized like that might be confusing it

Bujju•2y ago

It's at File.Create(_fileName).Close();

Anton•2y ago

but in general, reading files in a constructor that's called in static context might not be the best idea

Bujju•2y ago

When I hover over _fileName, it says it isn't null, but that's where it throws the exception

Anton•2y ago

a constructor reading files is already cursed to me

Bujju•2y ago

So I should move it to a method?

Anton•2y ago

absolutely that however is not the problem here you sure it doesn't fail on the second line? where you deserialize ah hold on when deserializing it calls the constructor again probably with a null argument

Bujju•2y ago

It's a different constructer

Anton•2y ago

which is absolutely cursed you sure it calls private constructirs by default?

Bujju•2y ago

That's the only parameterless constructer

Anton•2y ago

it bet it favors public ones if there are any and tries to match parameters by name or passes nulls try making it public it might actually just work

Bujju•2y ago

Oh wait it works now without making it public By moving it to a method

Anton•2y ago

did you turn that into a method? ok delay, sorry so your deserializer most likely favored the public constructor, even though there was a parameterless one just because it was private, the serializer decided to ignore it and now that there's no public constructors, it's forced to use the only available one

Bujju•2y ago

Was the constructer called in a static context only cursed because it was reading a file, or is that still cursed

Anton•2y ago

I wouldn't make such things like config static at all. I'd load them in my main or wherever, and pass around explicitly or via dependency injection Reading a file in a constructor is definitely cursed

Bujju•2y ago

My Main method switches to an async task which is where the config is used

Anton•2y ago

storing config in a static variable — somewhat cursed, but ok for one-off apps or if you're just learning the basics I'd load the config, then pass the config to the task why should the task touch globals at all? if you can make the dependency on that config explicit, do it explicit dependencies are a good thing. they are more verbose, but they make your program a lot more tractable in the long run

Bujju•2y ago

So for every class that needs the config, I should make it into a non-static field and load it in the constructer?

Anton•2y ago

plus, if many tasks try to read that global at once, I think class initialization is under a lock, so they'd collectively sit and wait on the IO of loading the config from disk for no reason, blocking the worker threads, potentially wasting resources not load, pass it in as a parameter the loading shouldn't be done in the constructor in general, try to do the least work you can in the constructor the best constructor is one that just assigns fields

Bujju•2y ago

Okay thanks !solved

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ArgumentNullException when argument is not null