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StructureMap – Changing Configuration at Runtime

In the beginning (late 2003), there was attributes and there was a copious amount of Xml configuration, and I called it good.  Look Ma!  I can radically change the behavior of the code without recompiling, isn’t that a marvelous thing?  Then we started to use StructureMap on a real project and quickly realized that it would be very useful if we could override some services with mock objects in our unit tests.  In later projects I’ve run into scenarios where it would be valuable to put an object into StructureMap after it was created.  Other users have asked for the ability to load assemblies or modules of their system on demand so as to save memory.  A major goal of the StructureMap 2.5 release has been to greatly extend its capabilities for service registration at runtime.  With a very few exceptions, you can now make any and all configuration changes after the first call to ObjectFactory.  My recommendation is to use this behavior simply and with caution because it will bypass many of the diagnostic abilities built into StructureMap (i.e. StructureMapDoctor might miss configuration problems introduced outside of the normal configuration).

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Adding Configuration to an Existing Container

In contrast to Initialize(), the Configure() method allows you to add additional configuration to an existing Container or ObjectFactory.  Think of this scenario.  You’re building a composite application that contains multiple modules spread over several assemblies, but you might not want to load any of the configuration or types for a particular module until it’s requested by the user.  In that case, you can use the Configure() method like this:

// This code would add any configuration from // Registry classes found in the // assembly named 'MyApplication.Module1' ObjectFactory.Configure(x => { x.Scan(scan => { scan.LookForRegistries(); scan.Assembly("MyApplication.Module1"); }); });

To summarize, Initialize() completely resets the configuration of a Container, and Configure() is purely additive.  If Configure() should happen to be called before Initialize(), it will set up the Container with the configuration in the Configure() call.  Configure() offers a subset of the Initialize() method (it leaves out the directives for the StructureMap.config file), and it also exposes the entire Registry DSL.  You can take advantage of that fact to add a few types or instances at a time:

ObjectFactory.Configure(x => { x.ForRequestedType<ISomething>().TheDefaultIsConcreteType<SomethingOne>(); });

Injecting a Single Service at Runtime

In my desktop applications the main form usually implements some sort of IApplicationShell interface.  I’ve found it valuable to place the main form itself into StructureMap, as well as several child controls of the main form as well so that various Controllers, Presenters, and Commands can interact with parts of the main shell without tight coupling.  I probably could build the ApplicationShell itself inside of StructureMap, but the child controls like (I’m making this up) IQueryToolBar or IExplorerPane are easiest to create as part of the ApplicationShell and loaded into StructureMap later.

public class ApplicationShell : Form, IApplicationShell
public IQueryToolBar QueryToolBar...
public IExplorerPane ExplorerPane...

Easy enough.  The main shell has some controls on it.  Now, we may want a centralized class to govern the behavior of just the query tool bar along the top of the main form.  That class obviously needs to find the IQueryToolBar on the main form, but I need a clean way of connecting the IQueryToolBar to this new QueryController class.

public class QueryController
private IQueryToolBar _toolBar;
public QueryController(IQueryToolBar toolBar)
_toolBar = toolBar;

StructureMap is going to build up the QueryController, but it doesn’t help to inject in a new IQueryToolBar that isn’t visible anywhere in the application.  We need to get to exactly the right instance of that control.  So let’s use the new Inject<T>(T instance) method on ObjectFactory to register the child controls from the main form.

// Familiar stuff for the average WinForms or WPF developer
// Create the main form
ApplicationShell shell = new ApplicationShell();
// Put the main form, and some of its children into StructureMap
// where other Controllers and Commands can get to them
// without being coupled to the main form

Now, a call to ObjectFactory.GetInstance<QueryController>() will poke the IQueryToolBar instance we registered above into the constructor of the new QueryController object.  Remember, one of the primary usages of StructureMap is simply to get the right service dependencies and metadata to the right concrete classes so you can concentrate on doing QueryController stuff in the QueryController class instead of bootstrapping all the stuff it needs.

I’ve used this exact strategy on three applications now to great success.  The previous design had a lot of “thisThing.ThatThing.QueryToolBar” (who needs the Law of Demeter?) properties just to get access to the child controls on the main form.  It was devolving into spaghetti code before I adopted the strategy above.

The ObjectFactory.Inject<T>(T instance) method is identical to the older ObjectFactory.InjectStub<T>(T stub) method.  I’ve marked the older method as deprecated because I think the name is misleading.

Use this strategy for any type of service or component that you need to inject into other services, but isn’t convenient or possible to build through StructureMap itself.

Injecting a Mock or a Stub at Runtime

On its maiden cruise in 2004, my team quickly realized that we needed a way to On its maiden cruise in 2004, my team quickly realized that we needed a way to make StructureMap deliver up mock objects in unit tests.  It obviously isn’t efficient to mock with an Xml file for each and every unit test that requires this function (don’t laugh, I’ve seen people do that with early versions of a StructureMap container), so we wanted a way to temporarily load ObjectFactory up with a mock object in place of its normal behavior for a given type.  Originally, there was hard coded support for the NMock framework, but with the advent of Rhino Mocks and other new mocking frameworks, I’ve removed that functionality in favor of the simple ObjectFactory/Container.Inject<T>(T object) methods.

My strong advice is to not use the Container or ObjectFactory in unit tests in the mass majority of cases.  Rather, my advice is to use simple Dependency Injection to inject mock objects during unit tests.  However, there are still times when you want or need a class to use the Container or ObjectFactory itself to get dependencies at runtime.  For that case, here is a sample:

public class MockingExample
public void SetUp()
// Make sure that the container is bootstrapped
public void TearDown()
// The problem with injecting mocks is in keeping the
// mocks from one test getting into another test.
// If you build the Container individually for each test run,
// this isn't a problem.  However, if you do inject mocks into
// the ObjectFactory static container, use the ResetDefaults()
// method in the [TearDown] (or Dispose() for xUnit.net) to clear
// out runtime injected services between tests
public void unit_test_that_uses_a_mock()
// Create a mock object with Rhino Mocks
var serviceMock = MockRepository.GenerateMock<IService>();
// or
ObjectFactory.Inject("theService", serviceMock);
// WARNING!  Inject is a generic method
// This method registers serviceMock as an "IService"
// and is NOT equivalent to:

Please note that the call to Inject<T>(T object) registers the mock object as the default for the PluginType “T.”  With RhinoMocks (my mocking tool of choice) this hasn’t been as issue because you create mock objects as the interface in question.  I have seen confusion with using other mocking engines that return the mock objects as “object” (I’m looking at you TypeMock).  In that case, be careful to include the generic parameter in the call to Inject<T>() to avoid registering your new mock object as “object.”

Ejecting all Instances of a PluginType

From a user request, StructureMap 2.5.2 introduces the ability to remove all Instances of a given PluginType by calling the Container.EjectAllInstancesOf<T>() method, where “T” is the PluginType.  This functionality will remove all object instances of T that are cached with the Singleton scope, but has no effect on other scopes.

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