I've been searching over the web how could I resolve instance using Prism DryIOC that uses parameter during runtime, but to luck yet.
For example, I have a class:
internal sealed class ItemInfoHelper : IItemInfoHelper
{
//ctor
public ItemInfoHelper(Item item) {...}
public string GetSomething() {...}
}
And in registering service I need to register it.
protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.Register<IItemInfoHelper, ItemInfoHelper>();
}
If I do this, when I resolve it somewhere like:
var helperInstance = container.Resolve<IItemInfoHelper>();
it will be obviously resolved using empty Item (using default Item constructor). I have seen a lot of examples that register instances using some parameters that are known at compile time. But the case is that I would like to resolve instance being initialized dynamically using Item that would be a different one in different places (i.e. known at runtime only).
Is there a way to register/resolve it using such behavior if I use Prism + DryIoc?
Thanks in advance.
The simplest type-safe way to do so is to resolve the function of item:
var getHelperInstance = container.Resolve<Func<Item, IItemInfoHelper>>();
var helperInstance = getHelperInstance(myItem);
Related
I have been struggling to get NopCommerce to pick up a registered interface.
This line here
this._connectionService = EngineContext.Current.Resolve<IConnectionService>();
is causing the error
Instances cannot be resolved and nested lifetimes cannot be created from this LifetimeScope as it has already been disposed.
I have registered the interface in the DependencyRegistrar
builder.RegisterType<ConnectionService>().As<IConnectionService>().InstancePerLifetimeScope();
The issue is that it works when the constructor is called once, but when the constructor is called again the interface has been disposed, the constructor is as seen below -
public ClientHub()
{
this._connectionService = EngineContext.Current.Resolve<IConnectionService>();
}
By default NopCommerce has a lot of registered interface already so I have tried using what looks like a cached version
builder.RegisterType<CustomerActivityService>().As<ICustomerActivityService>()
.WithParameter(ResolvedParameter.ForNamed<ICacheManager>("nop_cache_static"))
.InstancePerLifetimeScope();
But I still get an error when trying to use the ConnectionService like this.
I have tried using multiple different methods on the builder such as
InstancePerHttpRequest();
and
InstancePerDependency();
But it's all being disposed of when the constructor is called a second time, I did head over to the NopCommerce for any help but no luck.
Any guidance / help would be amazing !
public ClientHub()
{
this._connectionService = EngineContext.Current.Resolve<IConnectionService>();
}
well, that may create an issue, you're trying to resolve dependency, but that messed up.
It could be:
private readonly IConnectionService _connectionService
public ClientHub(IConnectionService connectionService)
{
this._connectionService = connectionService;
}
Or either it could be only:
private readonly IConnectionService _connectionService = EngineContext.Current.Resolve<IConnectionService>();
And not in constructor.
i'm looking for a larger example of dependency injection and how it can be implemented. If class A depends on class B and passes a reference of class C to B's constructor, must not class A also take a reference to class C in it's constructor? This means that the main method in the application should create all classes really, which sounds wierd?
I understand that using DI frameworks we can have it in XML files somehow, but that sounds like it could be hard to quickly see what type that really is instanciated? Especially if it a very large application.
You are correct and each DI framework has a different way of managing it.
Some use attributes on the properties etc to denote dependency and then "automagically" supply an instance of the correct type, while others (say castle windsor for .net) allow xml configuration, fluent or other methods for "wiring up" the dependency graph.
Also no, class A takes a built reference to an instance of B which was built using an instance of C. A needs to know nothing about C unless exposed via B.
public class C { }
public class B { public B(C c) { ... }}
public class A { public A(B b) { ... }}
// manual wireup
C c = new C();
B b = new B(c);
A a = new A(b);
// DI framework
InversionOfControlContainer container = new InversionOfControlContainer(... some configuration);
A a = container.ResolveInstanceOf<A>();
// container dynamically resolves the dependencies of A.
// it doesnt matter if the dependency chain on A is 100 classes long or 3.
// you need an instance of A and it will give you one.
Hope that helps.
to answer your question about classes A,B,and C, A only needs a reference to B.
Most DI frameworks do not require you to use XML for configuration. In fact, many people prefer not to use it. You can explicitly set things up in code, or use some kind of conventions or attributes for the container to infer what objects should fulfil dependencies.
Most DI frameworks have a facility for "lazy loading" to avoid the creation of every single class up front. Or you could inject your own "factory or builder" objects to create things closer to the time when they will be used
You've not said what language you are using. My example below is in C# using the Unity container. (obviously normally you would use interfaces rather than concrete types):
container = new UnityContainer();
container.RegisterType<C>();
container.RegisterType<B>();
A a = container.Resolve<A>();
here's a few examples from the PHP Language, hope this helps you understand
class Users
{
var $Database;
public function __construct(Database $DB)
{
$this->Database = $DB;
}
}
$Database = Database::getInstance();
$Users = new Users($Database);
From this example the new keyword is used in the method getInstance(), you can also do
$Users = new Users(Database::getInstance());
Or another way to tackle this is
class Users
{
/*Dependencies*/
private $database,$fileWriter;
public function addDependency($Name,$Object)
{
$this->$Name = $Object;
return $this;
}
}
$Users = new Users();
$Users->addDependency('database',new Database)->addDependency('fileWriter',new FileWriter);
Update:
to be honest, I never use Dependency Injection as all its doing is passing objects into classes to create a local scope.
I tend to create a global entity, and store objects within that so there only ever stored in 1 variable.
Let me show you a small example:
abstract class Registry
{
static $objects = array();
public function get($name)
{
return isset(self::$objects[$name]) ? self::$objects[$name] : null;
}
public function set($name,$object)
{
self::$objects[$name] = $object;
}
}
Ok the beauty of this type of class is
its very lightweight
it has a global scope
you can store anything such as resources
When your system loads up and your including and initializing all your objects you can just store them in here like so:
Registry::add('Database',new Database());
Registry::add('Reporter',new Reporter());
Where ever you are within your runtime you can just use this like a global variable:
class Users
{
public function getUserById($id)
{
$query = "SELECT * FROM users WHERE user_id = :id";
$resource = Registry::get("Database")->prepare($query);
$resource->bindParam(':id',$id,PDO::PARAM_INT);
if($resource->execute())
{
//etc
}else
{
Registry::get('Reporter')->Add("Unable to select getUserById");
}
}
}
i see this way of object passing is much cleaner
If anybody is still looking for a good example which shows DI without IoC Containers (poor man's DI) and also with IoC Container (Unity in this example) and registering the types in code and also in XML you can check this out: https://dannyvanderkraan.wordpress.com/2015/06/15/real-world-example-of-dependeny-injection/
First of all I would like to remark I am new with the concept of prism, DI and containers. I am looking on one of the code samples provided with the Prism Library:
The code simply injects a view with the "Hello World" string (in a TextBlock element) to a region in the shell.
When the application starts-up, it creates a new BootStrapper instance, which creates and initializes the shell:
public class Bootstrapper : UnityBootstrapper
{
protected override DependencyObject CreateShell()
{
return Container.Resolve<Shell>();
}
protected override void InitializeShell()
{
base.InitializeShell();
Application.Current.RootVisual = (UIElement)this.Shell;
}
protected override void ConfigureModuleCatalog()
{
base.ConfigureModuleCatalog();
ModuleCatalog moduleCatalog = (ModuleCatalog)this.ModuleCatalog;
moduleCatalog.AddModule(typeof(HelloWorldModule.HelloWorldModule));
}
}
My question refers to the method CreateShell(). I couldnt find nowhere in the supplied code (including not in a configuration file or any xaml file...) where do they register the type Shell, and even if it was registered - the supplies Shell class doesnt implement any interface... what is the meaning of resolving a specific type?
the Shell implementation:
public partial class Shell : UserControl
{
public Shell()
{
InitializeComponent();
}
}
This looks like a magic to me, so I tried to create my own type (MyType) and resolve it the same way:
Container.Resolve<MyType>();
By setting a breakepoint inside MyType constructor, I saw that it DID resolved MyType. Can somebody please explain to me how does it work?
These couple of threads should answer your question:
http://compositewpf.codeplex.com/Thread/View.aspx?ThreadId=230051
Does unity just make clasess with out needing anything registered?
Additionally, if you are eager to get more detail into how Unity can do this, simple download Unity 2.0 and open the source code that is provided with the installer.
I hope this helps.
Thanks,
Damian
You do not need to register a type you want to resolve. You need to register the dependencies of a type, that you want to resolve. In this case, the Shell doesn't need any dependencies, so you can resolve it simply. But for an example (not really), if your shell getting an interface IService as a parameter, then you must register IService, before you resolve Shell.
Otherwise you will get Dependency Resolution Failed Exception. In Prism 4.1 it will be swallowed silently due to TryResolve.
In the C# language, using StructureMap 2.5.4, targeting .NET Framework 3.5 libraries.
I've taken the step to support multiple Profiles in a structure map DI setup, using ServiceLocator model with Bootstrapper activation. First setup was loading default registry, using the scanner.
Now I like to determine runtime what Registry configuration I like to use. Scanning and loading multiple assemblies with registries.
Seems it's not working for the actual implementation (Getting the 202, default instance not found), but a stripped test version does work. The following setup.
Two assemblies containing Registries and implementations
Scanning them in running AppDomain, providing the shared Interface, and requesting Creation Of Instance, using the interfaces in constructor (which get dealt with thanx to the profile on Invokation)
Working code sample below (same structure for other setup, but with more complex stuff, that get's a 202):
What type of couses are possible for a 202, specifically naming the System.Uri type, not being handles by a default type?? (uri makes no sense)
// let structure map create instance of class tester, that provides the registered
// interfaces in the registries to the constructor of tester.
public class Tester<TPOCO>
{
private ITestMe<TPOCO> _tester;
public Tester(ITestMe<TPOCO> some)
{
_tester = some;
}
public string Exec()
{
return _tester.Execute();
}
}
public static class Main {
public void ExecuteDIFunction() {
ObjectFactory.GetInstance<Tester<string>>().Exec();
}
}
public class ImplementedTestMe<TSome> : ITestMe<TSome>
{
public string Execute()
{
return "Special Execution";
}
}
public class RegistryForSpecial : Registry
{
public RegistryForSpecial()
{
CreateProfile("Special",
gc =>
{
gc.For(typeof(ITestMe<>)).UseConcreteType(typeof(ImplementedTestMe<>));
});
}
}
Background articles on Profiles I used.
How to setup named instances using StructureMap profiles?
http://devlicio.us/blogs/derik_whittaker/archive/2009/01/07/setting-up-profiles-in-structuremap-2-5.aspx
http://structuremap.sourceforge.net/RegistryDSL.htm
EDIT:
It seemed the missing interface was actually the one being determined runtime. So here is the next challange (and solved):
I provided a default object whenever StructureMap needs to create the object. Like:
x.ForRequestedType<IConnectionContext>()
.TheDefault.Is.Object(new WebServiceConnection());
This way I got rid of the 202 error, because now a real instance could be used whever structure map needed the type.
Next was the override on runtime. That did not work out at first using the ObjectFactory.Configure method. Instead I used the ObjectFactory.Inject method to overide the default instance. Works like a charm.
ObjectFactory.Inject(typeof(IConnectionContext), context);
Loving the community effort.
Error code 202 means a default instance could not be built for the requested type. Your test code is apparently not equal to your real code that fails. If you are getting an error about Uri, you likely have a dependency that requires a Uri in its constructor. It may not be the class you are asking for - it may be one of that classes dependendencies - or one of the dependencies dependencies... somewhere down the line someone is asking StructureMap to resolve a Uri, which it cannot do, without some help from you.
High Level
With StructureMap, Can I define a assembly scan rule that for an interface IRequestService<T> will return the object named TRequestService
Examples:
FooRequestService is injected when IRequestService<FooRequest> is requested
BarRequestService is injected when IRequestService<BarRequest> is requested
Details
I have a generic interface defined
public interface IRequestService<T> where T : Request
{
Response TransformRequest(T request, User current);
}
and then I have multiple Request objects that implement this interface
public class FooRequestService : IRequestService<Foo>
{
public Response TransformRequest(Foo request, User current) { ... }
}
public class BarRequestService : IRequestService<Bar>
{
public Response TransformRequest(Bar request, User current) { ... }
}
Now I am at the point where I need to register these classes so that StructureMap knows how to create them because in my controller I want have the following ctor (which I want StructureMap to inject a FooRequestService into)
public MyController(IRequestService<Foo> fooRequestService) { ... }
Right now to get around my issue I have implemented an empty interface and instead of having the FooRequestService implement the generic interface I have it implement this empty interface
public interface IFooRequestService : IRequestService<Foo> { }
Then my controllers ctor looks like so, which works with StructureMaps' Default Convention Scanner
public MyController(IFooRequestService fooRequestService) { ... }
How could I create a rule with StructureMap's assembly scanner to register all objects named TRequestService with IRequestService<T> (where T = "Foo", "Bar", etc) so that I don't have to create these empty Interface definitions?
To throw something else into the mix, where I am handling StructureMap's assembly scanning does not have any reference to the assembly that defines IRequestService<T> so this has to use some sort of reflection when doing this. I scanned the answer to "StructureMap Auto registration for generic types using Scan" but it seems as though that answer requires a reference to the assembly that contains the interface definition.
I am on the path of trying to write a custom StructureMap.Graph.ITypeScanner but I am kind of stuck on what to do there (mainly because I have little experience with reflection).
You are on the right path with the scanner. Thankfully there is one built into StructureMap. Unfortunately it is not yet, as of this writing, released. Get the latest from trunk and you will see a few new things available within the scanner configuration. An example for your needs is below.
public class MyRegistry : Registry
{
public MyRegistry()
{
Scan(x =>
{
x.TheCallingAssembly();
//x.AssembliesFromApplicationBaseDirectory();
x.WithDefaultConventions();
x.ConnectImplementationsToTypesClosing(typeof (IRequestService<>));
});
}
}
First you need to tell the scanner configuration which assemblies to include in the scan. The commented AssembliesFromApplicationBaseDirectory() method also might help if you are not doing a registry per assembly.
To get your generic types into the container use ConnectImplementationsToTypesClosing.
For an example on how to setup use registries when setting up the container see:
http://structuremap.sourceforge.net/ConfiguringStructureMap.htm
If you like you can skip using registries in general and just do a scan within ObjectFactory.Initialize.
Hope this helps.