Ninject constructor injection in WPF

Question

Is it possible to use ninject for dependency injection in such a way that the result would be something like the injection I can get in MVC. To elaborate, if I use the MVC ninject adapter I can declare my web controllers as having constructor parameters which would then automatically be injected by ninject.

However, I haven't found such a ninject extension for WPF, which would enable me to have a window such as this:

public partial class MainWindow : Window
{
    private readonly IService injectedService;
    public MainWindow(IService injectedService) 
    {
        this.injectedService = injectedService;
    }
}

I would like to do this without explicitly using the IKernel in my main application startup to obtain an instance of mainwindow. I'd much prefer to use the normal method of xaml configuration to obtain an instance of the main window and all subsequent windows.

Is this possible? Is there any way to hook into the object creation generated by xaml to modify it to use Ninject for constructor dependency injection.

I don't think such an extension exists, because in WPF you normally make use of the MVVM pattern and thus would inject the services into your ViewModel classes. — Daniel Hilgarth, Feb 06 '12 at 13:09
But isn't the models themselves created via the XAML as well? Admittedly, I'm not an expert on WPF but wouldn't the models then need the same sort of dependency injection? I'm concerned about having my container showing which would impede unit testing of the project. — Dervall, Feb 06 '12 at 13:24
No, the ViewModels are not created in XAML. They are created in the ViewModelLocator, see [here](http://windowsphonegeek.com/articles/Working-with-a-simple-ViewModelLocator-from-MVVM-Lite) for an example. Your Views or ViewModels don't know anything about your dependency injection container. — Daniel Hilgarth, Feb 06 '12 at 13:52
But the ViewModelLocator will know about it. I guess this is fine but that still feels like the servicelocator (anti)pattern to me, and an extra layer of wrapping around the injection kernel which could have been handled automatically. — Dervall, Feb 06 '12 at 14:00
It is neither, because the ViewModelLocator would be your composition root. — Daniel Hilgarth, Feb 06 '12 at 14:05

deltree · Accepted Answer · 2012-02-07T23:01:39.207

Based on the comments & your confusion, it looks like MVVM is a good match for you. The challenge is, LEARNING MVVM.

So crack open a good link and get rolling. MVVM is surprisingly easy to do, and it's pretty easy to wrap it all up with Ninject and put a bow on it.

The initial learning curve if you DON'T use a 3rd party library for Ninject + MVVM like I did, is a bit steep. So here's a couple of things I had to understand:

        DataContext="{Binding Path=ResultViewModel,Source={StaticResource ServiceLocator}}"

This little addition makes allows you to trigger ninject to get your viewmodel information from your XAML:

<Application.Resources>
    <ioc:NinjectServiceLocator x:Key="ServiceLocator" />
</Application.Resources>

this little trick allows you to assign that staticresource from your app.xaml file to the relevant class

public class NinjectServiceLocator
{
    private readonly IKernel kernel;

    public NinjectServiceLocator()
    {
        kernel = new StandardKernel(new MyMvvmModule());
    }

    public ResultViewModel ResultViewModel
    {
        get { return kernel.Get<ResultViewModel>(); }
    }
}

This is notable. Every viewmodel must be listed as a property in the ServiceLocator in order for Ninject to generate them. Finally, MyMvvmModule in the example above is the standard Ninject class where you stick your override for Load() and bind all your interfaces.

@Dervall Thanks. This kinda post is what I think Jeff Atwood envisioned for SO. I had a similar issue, so I shared the info I found out after researching it for hours, saving anyone in the future lots of time I hope. — deltree, Sep 18 '12 at 18:15

Ninject constructor injection in WPF

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