How to load after screen Actived?

[a44281071]

Suppose I have the following structure:

Shell
    Login
        Sign in
        Register         ​
   ​Main
       ​ LeftNavMenu for module list
        ModuleFirst : IMainModule
        ModuleSecond : IMainModule      ​

I will regist all modules for IMainModule, and inject modules in Main.

// ctor for MainViewModel.
public MainViewModel(IEnumerable<IMainModule> modules)

The first place of doubt: How to active first module after main module loaded (actived)?
The 1st way, Specify one in advance.

// class MainViewModel.
   ​public class MainViewModel : Conductor<IMainModule>.Collection.OneActive
   ​{
       ​public MainViewModel(IEnumerable<IMainModule> modules)
       ​{
           ​Items.AddRange(modules);
           ​ActiveItem = Items.FirstOrDefault();
       ​}
  ​}

The 2nd way, after parent active.

// class MainViewModel.
  ​​public class MainViewModel : Conductor<IMainModule>.Collection.OneActive
  ​​{
      ​​public MainViewModel(IEnumerable<IMainModule> modules)
      ​​{
          ​​Items.AddRange(modules);
      }
      protected override async Task OnInitializeAsync(CancellationToken cancellationToken)
      {
          await base.OnInitializeAsync(cancellationToken);
          ActiveItem = Items.FirstOrDefault();
      }
  ​​}

However, the above two methods will cause the view not to be displayed until inner module actived, so it's not very good.
So I can change active module from OnInitializeAsync to OnViewLoaded, But it can not await, it means we lost control of logic, override async methods has lost value too.

    // class MainViewModel.
    public class MainViewModel : Conductor<IMainModule>.Collection.OneActive
    {
        public MainViewModel(IEnumerable<IMainModule> modules)
        {
            Items.AddRange(modules);
            ActiveItem = Items.FirstOrDefault();
        }

        protected override void OnViewLoaded(object view)
        {
            base.OnViewLoaded(view);
            ActiveItem = Items.FirstOrDefault();
        }
    }
    // class FirstModuleViewModel
    public class ModuleFirst : IMainModule
    {
        // this is bad.
        protected override void OnViewLoaded(object view)
        {
            base.OnViewLoaded(view);
            _ = LoadDataFromWebApiAsync();
        }
    }