Using a generic ViewModel - wpf

Question

I have a WPF MVVM App, but I want my ViewModel to be generic. What the app is suppose to do is take some Data and do CRUD operations on it without knowing the Type of the data it's getting at the compile-time. So I declared my ViewModel like this:
public class GenericViewModel<T> where T : class
{
private void ConstructorBase()
{
Type theType = typeof(T);
Properties = theType.GetProperties().ToList();
}
public GenericViewModel(DbContext _dbContextInsert) //pravi novi repository na osnovu DbContexta
{
ConstructorBase();
_R = new RepositoryGlobal<T>(_dbContextInsert);
}
public T newT { get; set; }
public T selectedT { get; set; }
public List<PropertyInfo> Properties { get; set; }
private RepositoryGlobal<T> _R;
}
Now, disregard almost everything you see inside it, the only important thing is that the Constructor is never reached. I set this ViewModel as the DataContext for the main window like this:
InitializeComponent();
this.DataContext = new GenericViewModel<Person>(new PersonDbContext());
But when I put a breakpoint inside the ViewModel's constructor, the program never gets stopped.
Any ideas?

Answer 1

Dependencies should be abstractions, not implementations.
Your generic view model should not create it's own repository, instead you should pass in an instance of this dependency via the constructor.
public class GenericViewModel<T> where T : class
{
protected readonly IRepository<T> _Repository;
public GenericViewModel(IRepository<T> repository)
{
_Repository = repository;
}
...
}
You would then create an instance of your repository like so:
DbContext context = new PersonDbContext();
IRepository<Person> personRepo = new PersonRepository(context);
GenericViewModel<Person> personViewModel = new GenericViewModel<Person>(personRepo);
There, your View Model's dependencies are no longer tied to a specific implementation, your code is now far more adaptable to changes. Not to mention massively easier to test.