Window dependency injection

Question

I want to use Unity dependency injection in WPF application. My Window throw System.Windows.Markup.XamlParseException:

"For type MainWindow found no default constructor".

This is my code:

App.xaml.cs:

IUnityContainer container = new UnityContainer();
container.RegisterType<MainWindow>();
container.RegisterType<IService, MyService>();
container.RegisterType<IRepository, MyRepository>();
container.Resolve<MainWindow>().Show();

MainWindow.xaml.cs:

public MainWindow(IService service)
{
     InitializeComponent();
     service.Test();
}

@RBarryYoung It's not cool to change the title of a question to something utterly unrelated to what the question is actually about. — 15ee8f99-57ff-4f92-890c-b56153, Aug 01 '16 at 14:18
@EdPlunkett I was just trying to return it to what it was before you vandalized it. If you want to be snarky, use the comments. Using your site privileges to mutilate someone else's question to mock them is way over the line. — RBarryYoung, Aug 01 '16 at 14:23
@EdPlunkett: In particular this is not about a missing default constructor, it's rather why Unity is not using the dependency/contructor injection as expected. — Dirk Vollmar, Aug 01 '16 at 14:46

score 3 · Accepted Answer · edited Aug 01 '16 at 13:54

3

You always need to have a default constructor for your view in order for your WPF application to work properly.

public MainWindow()
{
     InitializeComponent();
}

and then define the parameterized constructor like this :

public MainWindow(IService service) : this()
{
     service.Test();
}

edited Aug 01 '16 at 13:54

Scott Chamberlain

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answered Aug 01 '16 at 13:08

ViVi

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2

You need the parameterized constructor to call the default constructor with a `:this()` at the end of the method signature. otherwise `InitializeComponent();` won't get called – Scott Chamberlain Aug 01 '16 at 13:53
2

Default ctor needed only if views instantiated via XAML, right? If we instantiate views from code, view is not nave to have default ctor. – tym32167 Aug 01 '16 at 14:07
Imho, this does not address the OPs problem of Unity not calling the parameterized constructor with constructor injection. – Dirk Vollmar Aug 01 '16 at 14:50
I agree with @tym32167. But this is a **MainWindow**. How does it work without a default constructor, even if we write everything in code behind? – ViVi Aug 01 '16 at 16:57
@Scott Chamberlain : Sorry I missed it. Thanks for the edit. – ViVi Aug 01 '16 at 16:59
@IDisposable It will work ok, if you are using some DI container to create an instance of MainWindow (as example https://github.com/tym32167/arma3beclient/blob/c53fc1e97794d900e508ae425298e05b90c765c2/src/Arma3BE.Client/Bootstrapper.cs#L26 ) – tym32167 Aug 01 '16 at 18:18

Window dependency injection

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