Modern programmers require some means of creating new classes out of other classes that are passed as parameters, and to do so in an elegant, seamless manner. Those new instances often require caching, especially if they are services or view models. The got-to solution for this challenge has been the mis-named and grossly mis-described "IOC Container". If we can't even name something accurately, it is time to reconsider it entirely. So I have done that here with the tool that all of us actually need: a DI ("Dependency Injection") Container.
IOC containers always store an instance when you create it. That is extremely wasteful. The Smart DI Container provides only three types of registrations:
Use these to create instances at any time and without caching. The local variable you retrieve on Resolve() is the only stored reference.
When you Resolve() using this access level, you must to pass in a "parent" object that gets indexed to that new class instance. You can also link the same instance to any number of other consumers/parents by calling Resolve() again. Once all of the parents die, the cached instance is also removed.
Note: This requires you to raise the ObjectDisappearingMessage to notify the container about the death of a shared instance parent. That message is declared in our Shared Forms Library, which you can import from Nuget.
We can do this for you if you also use our a few other simple libraries:
SmartDI.LifecycleAware. NuGet.
There's also a handy sample app here and on Nuget.
In spite of the ginormous size of other containers on the market, none of them can pass this test. The container must provide a physical mechanism to make this functionality possible. We have one!
The container creates and caches a permanent instance of any type registered with this access level. The cached reference dies when the container itself falls out of scope.
You can declare an instance of the Smart DI Container wherever you please. This supports "nested" scenarios, where containers live within narrowly defined class inheritance trees. Remember: all "global" variables stored/cached will only live as long as the container does.
This container protects against recursive calls, or any other violation of the rules-based registrations you make. For instance, if you register two competing interfaces for the same base type:
_container = new SmartDIContainer();
_container.RegisterTypeAsInterface<FirstSimpleClass>(typeof(IAmSimple));
_container.RegisterTypeAsInterface<SecondSimpleClass>(typeof(IAmSimple));... and then resolve IAmSimple, you have created a conflict. The container cannot know which one to return. You can set a Boolean property to throw an error in this case. Or you can provide a conflict resolver:
var simple =
_container.Resolve<IAmSimple>(
StorageRules.AnyAccessLevel, null, ForbidSpecificClass<FirstSimpleClass>);
private static IConflictResolution ForbidSpecificClass<T>(
IDictionary<Type,
ITimeStampedCreatorAndStorageRules> registrations)
{
// Find any registration where the key
// (the main class that was registered and that is being constructed)
// is *not* the forbidden one
var legalValues = registrations.Where(r => r.Key != typeof(T)).ToArray();
if (legalValues.IsEmpty())
{
return null;
}
return
new ConflictResolution
{
MasterType = legalValues.First().Key,
TypeToCastWithStorageRule =
legalValues.First().Value.CreatorsAndStorageRules.First()
};
}
}It occupies almost no space at all, and rarely touches memory, since it does not store anything unnecessarily.
We actually added comments! (And we were not struck by lightning)
See the unit tests.
Please also refer to the Quick Start Guide.
