C#•3mo ago

✅ Which is the more correct way of class instantiation?

// app.axaml.cs
public override void OnFrameworkInitializationCompleted()
{
    if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
    {
        Helpers hp = new();

        desktop.MainWindow = new MainWindow
        {
            DataContext = new MainWindowViewModel(hp),
        };
    }

    base.OnFrameworkInitializationCompleted();
}

// app.axaml.cs
public override void OnFrameworkInitializationCompleted()
{
    if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
    {
        Helpers hp = new();

        desktop.MainWindow = new MainWindow
        {
            DataContext = new MainWindowViewModel(hp),
        };
    }

    base.OnFrameworkInitializationCompleted();
}

// MainWindowViewModel.cs
public class MainWindowViewModel : ViewModelBase
{
  private Helpers _hp = new();

  // this part is 100% optional. You can use helpers as _hp as well
  public Helpers Hp
  {
      get => _hp;
      set => this.RaiseAndSetIfChanged(ref _hp, value);
  }
}

// MainWindowViewModel.cs
public class MainWindowViewModel : ViewModelBase
{
  private Helpers _hp = new();

  // this part is 100% optional. You can use helpers as _hp as well
  public Helpers Hp
  {
      get => _hp;
      set => this.RaiseAndSetIfChanged(ref _hp, value);
  }
}

Is it better to instantiate your used objects like this in the app.axaml.cs file and then pass them off to the main window view model like the public override function at the top or is it better to instantiate your used objects in the main window view model like the code block underneath it? I ask because I've noticed that when I build a new view model, if I instantiate the items I need right there in the class as new instances of that item, I don't have the need for two constructors like

public MainWindowViewModel()
{
    Text = "Hello World!";
}
public MainWindowViewModel(Helpers hp)
{
    _hp = hp;
}

public MainWindowViewModel()
{
    Text = "Hello World!";
}
public MainWindowViewModel(Helpers hp)
{
    _hp = hp;
}

so I'm just curious to if it's user preference, or which is more correct

12 Replies

Pobiega•3mo ago

Depends on a few things. First, the parameterless constructor implies that the helper object is optional But it's not declared as such, so that's an orange flag. However, beyond that it's really up to you if you want to do inversion of control or not

Mekasu0124•3mo ago

the only reason I have two constructors is because when I pass variables from the previous file to the next file, I get an error saying that the view model can't find a good enough constructor I forgot to put the : this() on the one that is supposed to be called

Pobiega•3mo ago

Taking the dependency as a constructor parameter let's you easily use DI for example But if you dont plan on using DI, there isn't much to win

Mekasu0124•3mo ago

DI means dependency injection, right?

Pobiega•3mo ago

Yup

Mekasu0124•3mo ago

so passing the instance from app.axaml.cs to MWVM is DI when I use that passed object in the MWVM ok so I'm still not quite satisfied. Which is better? DI or new instantiations in each view model and other classes (creating multiple instances)?

Pobiega•3mo ago

Depends. Does the helper class have internal state that shouldn't be mixed across multiple windows? If it does, don't inject the same instance If it doesn't, can the helper be static?

Mekasu0124•3mo ago

public class Helpers
{
    private static readonly string _tosPath = Directory.GetCurrentDirectory() + "/MakeMyProject/TermsOfService.txt";

    internal string GetTosText()
    {
        var fileData = File.ReadAllText(_tosPath);

        if (fileData != null)
        {
            return fileData;
        }
        else
        {
            return """
                    No Tos Text Was Found

                    If you believe this to be in error then try restarting
                    the program, otherwise, please create a new issue on
                    the github repo page.

                    -Mekasu
                   """;
        }
    }
}

public class Helpers
{
    private static readonly string _tosPath = Directory.GetCurrentDirectory() + "/MakeMyProject/TermsOfService.txt";

    internal string GetTosText()
    {
        var fileData = File.ReadAllText(_tosPath);

        if (fileData != null)
        {
            return fileData;
        }
        else
        {
            return """
                    No Tos Text Was Found

                    If you believe this to be in error then try restarting
                    the program, otherwise, please create a new issue on
                    the github repo page.

                    -Mekasu
                   """;
        }
    }
}

this is one of my helper files. The other one is a JsonEngine which is a public class with internal functions

Pobiega•3mo ago

This one seems as if it could be static, techically but if we disregard that and speak about the concept generally, I'd usually recommend passing them in via the constructor, as it gives more freedom you can tweak what VMs share what dependencies as you need - new every time, partial sharing, full sharing, etc

Mekasu0124•3mo ago

gotcha. thanks! just to be sure I understand the lingo.

This one seems as if it could be static, technically

public class MainWindowViewModel : ViewModelBase
{
  ViewModelBase _content = new();

- private Helpers _hp = new();
- private JsonEngine _jsEngine = new();

- public MainWindowViewModel(Helpers hp, JsonEngine jsEngine)
+ public MainWindowViewModel()
  {
-    UsersModel model = JsEngine.CreateUsersFile();
+    UsersModel model = JsonEngine.CreateUsersFile();
  }

- public Helpers Hp
- {
-    get => _hp;
-    set => this.RaiseAndSetIfChanged(ref _hp, value);
- }

- public JsonEngine JsEngine
- {
-    get => _jsEngine;
-    set => this.RaiseAndSetIfChanged(ref _jsEngine, value);
- }
}

public class MainWindowViewModel : ViewModelBase
{
  ViewModelBase _content = new();

- private Helpers _hp = new();
- private JsonEngine _jsEngine = new();

- public MainWindowViewModel(Helpers hp, JsonEngine jsEngine)
+ public MainWindowViewModel()
  {
-    UsersModel model = JsEngine.CreateUsersFile();
+    UsersModel model = JsonEngine.CreateUsersFile();
  }

- public Helpers Hp
- {
-    get => _hp;
-    set => this.RaiseAndSetIfChanged(ref _hp, value);
- }

- public JsonEngine JsEngine
- {
-    get => _jsEngine;
-    set => this.RaiseAndSetIfChanged(ref _jsEngine, value);
- }
}

right?

Pobiega•3mo ago

Yeah, pretty much

Mekasu0124•3mo ago

ok bet. ty

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✅ Which is the more correct way of class instantiation?