Question

I am very new to using dependency injection, and I am trying it out with Ninject in my WPF application. I was wondering how should I be passing parameters across classes.

For e.g.

public class ViewPersonViewModel : ViewModelBase
{
    private IDataAccessService _dataService;
    private IPerson _person;
    private string _remarks;

    // binded to textbox
    public string Remarks
    {
        get { return _remarks; }
        set {
            if (_remarks != value) {
                remarks = value;
                OnPropertyChanged("Remarks");
            }
        }   
    }

    public ViewPersonViewModel(
        IDataAccessService dataService, IPerson person)
    {
        _dataService= dataService;
        _person = person;
    }

    // binded to Button
    public void RetrieveStatus()
    {
        Remarks = _dataService.RetrieveRemarks(_person);
    }
}

In here, dataService is a fixed class, where I presumably can do

class Module : Ninject.Modules.NinjectModule 
{
    public override void Load() 
    {
        Bind<IDataAccessService>().To<DefaultDataAccessService>();
    }
}

But I will like to know how should I handle the person parameter, where it is set by the calling class.

I saw from Creating an instance using Ninject with additional parameters in the constructor that it is possible to pass additional parameters in the constructor.

However, I have a few concerns:

1. Is using kernel.Get<MyClass>( With.Parameters.ConstructorArgument( "parameterName", parameterValue) ); an ideal way? Wouldn’t it cause a lot of problems in debugging such as when you have typed your parameterName by mistake?

2. Ruben also mentioned about using a more complicated way where Provider is involved. Is it applicable here? If it is, how can I use it?

Answer 1

Ninject 3 provided a convenient function that allows me to pass the parameters across classes. By creating an interface like

public interface IViewPersonViewModelFactory()
{
    IViewPersonViewModel CreateViewPersonViewModel([parameterType parameterName..]);
}

and adding the following to the Ninject module to be loaded:

public override void Load()
{
    Bind<IMainControllingViewModelFactory>().ToFactory();
    ... ... //other bindings
}

We can then obtain an instance of the ViewPersonViewModel class (for e.g. in the MainViewModel class)

 public class MainViewModel
 {
     private IViewPersonViewModel _viewModel;

     public MainViewModel(IViewPersonViewModelFactory viewModelFactory)
     {
         _viewModel = viewModelFactory.CreateViewPersonViewModel(parameters..);
     }
 }

Note that no concrete factory has to be created.

The wiki can be found at: https://github.com/ninject/ninject.extensions.factory/wiki/Factory-interface