Is it normal to pass many interfaces in ViewModel constructor using DI container in WPF

Question

I have a huge WPF project. It uses:

MVVM Light
Microsoft.Unity container as a ViewModelLocator

The MainView content depends from other UserControls:

<ContentControl  Visibility="Visible"
                 Content="{Binding ContentViewModel}" />

Each ViewModel for content creates by ConcreateViewModelFactory:

 ContentViewModel =(SimpleViewModelBase)  _extendedSearchVMFactory.CreateInstance();

All ViewModels factories has interfaces that registered in ViewModelLocator. Factory example:

public class MainViewModelFactory : IMainViewModelFactory
{
    private IUnityContainer _container;

    public MainViewModelFactory(IUnityContainer container)
    {
        _container = container;
    }

    public MainViewModel CreateInstance(df_role[] currentRoles)
    {
        var vm = _container.Resolve<MainViewModel>(
            new ParameterOverride("currentRoles", currentRoles));
        return vm;
    }
}

MainViewModel costructor has about 40 parameters to keep all Interfaces for ViewModel constructors:

public MainViewModel(IDataService dataService,
        IDialogService dialogService,
        ISearchByIdViewModelFactory searchViewModelFactory,
        ISearchByPhonesViewModelFactory searchByPhonesViewModelFactory,
        IDoubleSearcherViewModelFactory doubleSearcherViewModelFactory,
        IAnalysisOfDoubleSearchAlgorythmViewModelFactory analysisOfDoubleSearchAlgorythmViewModelFactory,...

My question: How can I refactor this? If you have helpful information about DI+MVVM I will be grateful.

P.S. Sorry for my english.

If it takes 40 parameters probably it does a lot of work. You need to separate the responsibilities and move group of objects to a separate class. Then you can inject the newly created collaborator to your MainViewModel. — Sriram Sakthivel
Well going by your title "Is it normal to pass many interfaces in ViewModel constructor using DI container in WPF" - WPF has no dependency (no pun intended) on DI so "Is it normal" would have to depend on your choice of a DI system. I don't know much about the DI you are using, but if you were using Microsoft MEF then your constructor would be normally parameter-less. MEF injects values into properties, not into constructors. 40 parameters would strike me as a sign of bad design on your part — MickyD
As the others have said, separate the responsibility of the view model into services, and have those injected instead. That way, you may only need to inject a max of 5 services. This should also make the view model easier to unit test. — Falgantil
I agree with @SriramSakthivel. Check out this article for some guidance. — EagleBeak

Vinkal Vinkal · Accepted Answer · 2015-02-02T15:45:08

MainViewModel constructor has many parameters. MainViewModel violates "Single Responsibility Principle". Ideally any class should not have many responsibility.

Please go through the links below to understand Single Responsibility Principle.

http://www.codeproject.com/Articles/703634/SOLID-architecture-principles using-simple-Csharp

The link #1 talks about SOLID Architecture Principle

SOLID stands for: "S" - SRP (Single responsibility principle) “O” - Open closed principle “L”- LSP (Liskov substitution principle) “I” - ISP (Interface Segregation principle) “D” - Dependency inversion principle.

MVVM: To understand MVVM, please go through the link below

https://msdn.microsoft.com/en-us/magazine/dd419663.aspx

Is it normal to pass many interfaces in ViewModel constructor using DI container in WPF

1 Answers