I am using MEF as an IOC in my application. I found myself stuck in a situation where I need exactly two instance at a time for a class in my application (across all threads). I thought it would be easy just by adding export attribute twice with different container name and then using that container name to create two instances.
[Export("Condition-1",typeof(MyClass)]
[Export("Condition-2",typeof(MyClass)]
[PartCreationPolicy(System.ComponentModel.Composition.CreationPolicy.Shared)]
public class MyClass { }
And then export them as
Container.GetExport<MyClass>("Condition-1").Value
Container.GetExport<MyClass>("Condition-2").Value
But this trick did not work. I finally able to solve my problem by using CompsositionBatch
cb.AddExportedValue<MyClass>("Condition-1",new MyClass());
cb.AddExportedValue<MyClass>("Condition-2",new MyClass());
But my question is, Why am I not able to get different instances on the basis of Contract Name. Is it right that Contract name does not matter if CreationPolicy is shared?
The problem is in the setup of PartCreationPolicyAttribute that decorates MyClass.
CreationPolicy.Shared means that a single instance will be returned for each call to Container.GetExport. It is like a singleton. What you need in your case is the CreationPolicy.NonShared policy which will return a different instance for each clla to Container.GetExport.
Here's a good article on Part Creation Policy.
Also have a look at ExportFactory in MEF 2 for MEF2 additions regarding the lifetime and sharing of parts
Related
I have a servicereference with a method I need to use in a test.
The servicereference class is defined as:
public class MyServiceReference : Clientbase<IMyServiceReference>, IMyServiceReference
{
public MyServiceReference()
{
}
..... methods is then defined
}
From my testmethod I have tried both
private MyServiceReference myServiceReferenceFake = A.Fake<MyServiceReference>();
// And
private MyServiceReference myServiceReference = new MyServiceReference();
For both of these is crashes in the constructor with the message:
System.InvalidOperationException: Could not find default endpoint element that references contract.
All I need is to have a callto definition from a method in that class.
How can this be solved?
I've no experience with Clientbase, which I assume to be a System.ServiceModel.ClientBase<TChannel>,but I can make some general comments.
Since you tried first to fake a MyServiceReference, I'll assume that you're not testing that class, and you want to use it as a collaborator for the system under test. In that case, your best bet is to try faking IMyServiceReference. interfaces are very easy to fake, since they don't bring along any behaviour or baggage like faking a class does.
If you feel you really need to fake a MyServiceReference, then we have to contend with the fact that FakeItEasy will eventually call MyServiceReference(), which will call ClientBase<IMyServiceReference>(), whose documentation says
Initializes a new instance of the ClientBase<TChannel> class using the default target endpoint from the application configuration file.
Based on the error you reported, I assume that the application configuration file is not found or does not include the configuration required to create a MyServiceReference. The fact that you get the same error when you just try to instantiate a MyServiceReference directly strengthens my belief.
So I think your paths forward are either to try faking IMyServiceReference or to provide the configuration that ClientBase<IMyServiceReference> needs.
I know how to add a Bean to a CDI container during AfterBeanDiscovery. My problem is that what I really need to do is the equivalent of adding a new producer method with the equivalent of a particularly qualified parameter.
That is, I'd like to somehow programmatically create several of these:
#Produces
#SomeQualifier("x")
private Foo makeFoo(#SomeQualifier("x") final FooMaker fm) {
return fm.makeFoo();
}
...where the domain over which SomeQualifier's value element ranges is known only at AfterBeanDiscovery time. In other words, some other portable extension has installed two FooMaker instances into the container: FooMaker-qualified-by-#SomeQualifier("x") and FooMaker-qualified-by-#SomeQualifier("y"). Now I need to do the equivalent of making two producer methods to "match" them.
Nonbinding is not an option; I want this resolution to take place at container startup, not at injection time.
I am aware of BeanManager's getProducerFactory method, but the dozens if not hundreds of lines of gymnastics I'd have to go through to add the right qualifier annotation on each AnnotatedParameter "reachable" from the AnnotatedMethod I'd have to create by hand (to avoid generics issues) make me think I'm way off the beaten path here.
Update: So in my extension, I have created a private static method that returns a Foo, and has a FooMaker parameter. I've wrapped this in a hand-tooled AnnotatedMethod that reports SomeQualifier("x") etc. in its getAnnotations() method, and also reports SomeQualifier("x") etc. from its AnnotatedParameter's getAnnotations() method. Then I got a ProducerFactory from the BeanManager and feed that into a new Bean that I create, where I use it to implement the create and destroy methods. Everything compiles and so forth just fine.
(However, Weld (in particular) blows up with this usage, which leads me to think that I'm doing Really Bad Things™.)
I'm in the process of trying to migrate a R# extension project from R# 6 to R# 8. (I've taken over a project that someone wrote, and I'm new to writing extensions.)
In the existing v6 project there is a class that derives from RenameWorkflow, and the constructor used to look like this;
public class RenameStepWorkflow : RenameWorkflow
{
public RenameStepWorkflow(ISolution Solution, string ActionId)
: base(Solution, ActionId)
{
}
This used to work in R# SDK v 6, but now in V8, RenameWorkflow no longer has a constructor that takes Solution and actionId. The new constructor signature now looks like this;
public RenameWorkflow(
IShellLocks locks,
SearchDomainFactory searchDomainFactory,
RenameRefactoringService renameRefactoringService,
ISolution solution,
string actionId);
now heres my problem that I need help with (I think)
I've copied the constructor, and now the constructor of this class has to satisfy these new dependancies. Through some digging I've managed to find a way to satisfy all the dependencies, except for 'SearchDomainFactory'. The closest I can come to instantiating via the updated constructor is as follows;
new RenameStepWorkflow(Solution.Locks, JetBrains.ReSharper.Psi.Search.SearchDomainFactory.Instance, RenameRefactoringService.Instance, this.Solution, null)
All looks good, except that JetBrains.ReSharper.Psi.Search.SearchDomainFactory.Instance is marked as Obsolete, and gives me a compile error that I cannot work around, even using #pragma does not allow me to compile the code. The exact error message I get when I compile is Error 16 'JetBrains.ReSharper.Psi.Search.SearchDomainFactory.Instance' is obsolete: 'Inject me!'
Obvious next question..ok, how? How do I 'inject you'? I cannot find any documentation over this new breaking change, in fact, I cannot find any documentation (or sample projects) that even mentions DrivenRefactoringWorkflow or RenameWorkflow, (the classes that now require the new SearchDomainFactory), or any information on SearchDomainFactory.Instance suddenly now obsolete and how to satisfy the need to 'inject' it.
Any help would be most appreciated! Thank you,
regards
Alan
ReSharper has its own IoC container, which is responsible for creating instances of classes, and "injecting" dependencies as constructor parameters. Classes marked with attributes such as [ShellComponent] or [SolutionComponent] are handled by the container, created when the application starts or a solution is loaded, respectively.
Dependencies should be injected as constructor parameters, rather than using methods like GetComponent<TDependency> or static Instance properties, as this allows the container to control dependency lifetime, and ensure you're depending on appropriate components, and not creating leaks - a shell component cannot depend on a solution component for instance, it won't exist when the shell component is being created.
ReSharper introduced the IoC container a few releases ago, and a large proportion of the codebase has been updated to use it correctly, but there are a few hold-outs, where things are still done in a less than ideal manner - static Instance properties and calls to GetComponent. This is what you've encountered. You should be able to get an instance of SearchDomainFactory by putting it as a constructor parameter in your component.
You can find out more about the Component Model (the IoC container and related functionality) in the devguide: https://www.jetbrains.com/resharper/devguide/Platform/ComponentModel.html
I am very new to concept of IOC and I understand the fact that they help us resolve different classes in different contexts. Your calling class will just interact with Interface and Interface with decide which implementation to give you and it takes care of newing up the object.
Please do correct me if I am understanding is wrong because my question is based on that:
Now, I see this pattern very often in these projects:
private readonly IEmailService emailService;
private readonly ITemplateRenderer templateRenderer;
private readonly IHtmlToTextTransformer htmlToTextTransformer;
public TemplateEmailService(IEmailService emailService,
ITemplateRenderer templateRenderer,
IHtmlToTextTransformer htmlToTextTransformer)
{
this.emailService = emailService;
this.htmlToTextTransformer = htmlToTextTransformer;
this.templateRenderer = templateRenderer;
}
I understand that this helps using all the implementations of these classes without newing them up and also you don't have to decide WHICH implementaion to get, your IOC decides it for you, right?
but when I code like this, I do not even touch any IOC congiguration files. And again I am usin git for 2 days only but from all the tutorials that I have read, I was expecting my self to configure something which says "Resolve IParent to Child" class. But it works without me doing anything like it. Is it because there is only one implementaion of these interfaces? and If I do have more than one implementations then and then only I will have to configure resolved explicitly?
The code sample you have is a case of Constructor Injection.
In a traditional code, you would have a parameterless constructor, and in it you would "new-up" your objects like this:
IEmailService emailService = new EmailService();
So your code is explictly controlling which implementation gets assigned to the interface variable.
In IoC using constructor injection, control is inverted, meaning the container is "driving the bus" and is creating your TemplateEmailService object. When it is about to create it, the container looks at your constructor parameters (IEmailService , ITemplateRenderer , etc.) and feeds those objects to your class for use.
The IoC container can be configured so that interface A gets fulfilled by implementation B (or C) explicitly. Each one has a way to do it. Or it could do it by convention (IFoo fulfilled by Foo), or even attributes in classes, whatever.
So to answer your question-- you can explicitly define which implementations get used to fulfill certain interfaces. Got to read the IoC container docs for how to.
One more thing - "when you code like this", you technically don't have to be using an IoC container. In fact, your class should not have a direct reference to the container - it will maximize the reusability, and also allow easy testing. So you would wire-up interfaces to implementation classes elsewhere.
I have a question that keeps bothering me. Currently, I have started using Kohana 3.2 Framework. I've written a helper to handle some functionality - I have a number of methods, which are (as it should be) declared STATIC. But, all of these methods are somehow working with the database, so I need to load a model. Currently, every method has a non-static variable like this:
$comment = new Model_Comments;
$comment->addComment("abc");
OK, it seems to be working, but then I wanted to get rid of this redundancy by using class attribute to hold the instance of the model (with is class as well).
Something like this:
private static $comment; // Declaring attribute
self::$comment = new Model_Comment; // This is done within helper __constuct method
self::$comment->addComment("abc"); // And call it within the method.
But, I got failed with: Call to a member function addComment() on a non-object
Question is: is it possible to do it ? Maybe there are some other approaches ?
Sorry for a long story and, thanks in advice! :P
A static method cannot call a non-static method without operating on an instance of the class. So, what you're proposing won't work. There may be a way do accomplish something similar, but what about trying the following:
You could implement the singleton or factory pattern for your "helper" class. Then, you could create the model (as an attribute) as you instantiate/return the instance. With an actual instance of your "helper" class, you won't have to worry about the static scope issues.
In other words, you can create a helper-like class as a "normal" class in your application that, upon creation, always has the necessary model available.
I'd be happy to help further if this approach makes sense.
David