CODEWITHSUNDEEP
c#ioc-containerstructuremap
Torbjörn Kalin
Torbjörn Kalin

Reputation: 1986

Resolve where transient instance is shared

I have the following object graph that I would like to resolve using an IoC container:

enter image description here

Here, B(#1) and B(#2) are of the same type but different instances, same with C(#1) and C(#2), and D(#1) and D(#2). I would like to resolve A.

The problem is that there are two instances of D that four other objects have as a dependency. Depending on how I set the lifecycle of D, I will either get one instance that all of them share, or I will get four different instances.

I am currencly using StructureMap, but the solution could use another IoC container if some feature is needed that StructureMap doesn't have.

The actual use case (as per request in the comments):

The object graph is found inside a WPF application where I have separated the responsibilities of the typical MVVM ViewModel into a ViewModel and a Controller. In the image above, D is a ViewModel that only contains the state and C is a Controller that executes commands. B is the DataContext that the XAML binds to.

B, C and D are part of a user control. A is a DataContext that contains two instances of the user control.

Upvotes: 2

Views: 182

Answers (2)

Steven
Steven

Reputation: 172646

I think the trick is to register D as per-request (which is StructureMap's default lifestyle) and make a registration for A that explicitly resolves the two B's:

For<A>().Use(s => 
{
    var b1 = s.GetInstance<B>();
    var b2 = s.GetInstance<B>();
    return new A(b1, b2);
});

This ensures that for each resolved graph of B, there will be exactly one D, and since your object graph probably consists of much more than just A, B, C, and D, this ensures that you only have to fall back to using manual wiring for A and this keeps your dependency graph the most maintainable.

Upvotes: 1

Kirill Bestemyanov
Kirill Bestemyanov

Reputation: 11964

You can use factory method:

For<B>().Use(s => 
{
    var d = s.GetInstance<D>();
    var c = new C(d);
    return new B(c,d);
});

Upvotes: 1

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