my controller class
IPaymentProcessor _paymentProcessor = ObjectFactory.Container.GetInstance<IPaymentProcessor>("cert5");
my IoC class
x.For<IX509Cert>().Use<X509Cert>().Ctor<string>().Is(Settings.GetCreditCardCertFile(5)).Named("cert5");
When using multiple credit card cert files it may be a better option to not use the IoC container. You can use an instance of the IPaymentprocesssor inside your controller directly instead.
Related
I'm trying to use Zenject in Unity. I have an interface and several implementations of it.
I want to inject with ID but also that the implementation will have the tick interface since it's not a MonoBehaviour.
So I have an IAttacker interface and a MeleeAttackImpl implementation.
Container.Bind<IAttacker>().WithId(AttackerTypeEnum.MELEEE).To<MeleeAttackImpl>().AsTransient();
I want to add
Container.BindInterfacesTo<MeleeAttackImpl>().AsTransient();
But it creates 2 different objects instead of instances that have the Tick interface and bind them to IAttacker.
If you want to bind an interface to a determined implementation, why do you use two bindings?
If you want only one instance of the object I would try:
Container.BindInterfacesAndSelfTo<MeleeAttackImpl>().AsSingle();
or:
Container.Bind<IAttacker>().To<MeleeAttackImpl>().AsSingle();
As Single() In the case you need the same instance provided from the container along the app (like a singleton).
From the documentation:
"AsTransient - Will not re-use the instance at all. Every time ContractType is requested, the DiContainer will execute the given construction method again."
Many times intance is created in the binding itself. So maybe from the two binding two instances are created, one from each binding.
In case you need to create instances dynamically with all their dependencies resolved, what you need a is Factory.
I've edited the question to make what I want to obtain clearer.
Here's the original question:
I'm working on a class that inherits from Control which will be used in my View and includes some Dependency Properties.
One of these DPs is an IEnumerable(Of RfidTag) and will be bound to an ObservableCollection(Of RfidTag) inside the VM.
The class RfidTag is defined as public class in the same file where the VM's class resides.
The questions are:
1. is it a good practice to expose a VM-related class to a Control class?
2. is the VM source file a good place for the RfidTag class?
UPDATE 1
In my application logic (I think I could say in my Model) there is an event published throught an Eventaggregator. The event's payload is a List of ModelRfidTag (that is the model class).
My VM subscribes to this event and I made the RfidTag class to wrap my Model class and provides some additional properties related only to the VM.
When the event handler inside the VM is executed, it makes an ObservableCollection(Of RfidTag) bindable from the view.
Then in the View I've a bounch of my control instances like that
<c:RfidTagPresenter
TagPosition="1"
Collection="{Binding RfidTagList, Mode=OneWay}" />
Then in my RfidTagPresenter (the class that inherits from Control) I've a DP of type RfidTag (called RfidTagResult) that returns the object in the OC which has the Position property (property available inside the RfidTag class) equal to the value set by the TagPosition DP.
In this way, the ControlTemplate of the RfidTagPresenter can bind its elements to the desired object.
This is the simplification of what I want to make. In the actual application there are some other DPs on which the RfidTagResult selection is performed
UPDATE 2
After a bit of research, seem that I can solve one problem with an indexed property that return (in the get method) the object from the collection I want to bind.
However a problem still exist: My control need to have a DP of type of RfidTag so that the relative ControlTemplate can bind to the property declared in the RfidTag class.
So: Is it possible (read: a good practice) to have a DP of a type that is a VM related class?
In other words: Can a custom control know about the class type used by the VM?
I will try to go all over your question (if I miss something let me know) but first you should explain the purpose of binding a Collection in a control as a DP.
is it a good practice to expose a VM-related class to a Control class?
RfidTag, I suppose, is a Model. What you are really doing here is binding a Model in your control which go against the MVVM pattern. You should think about the next question... Do you really need all your RfidTag to be shown in the View ? If you need to show a name, an ID... you could just create an IEnumerable<string> as DP (which is correct) and then in your VM instead of an ObservableCollection<RfidTag> you would have an ObservableCollection<string>.
Some simple theory. In MVVM, VM adapts the Model to the View. So your VM should have everything that will be shown in your View.
is the VM source file a good place for the RfidTag class?
RfidTag is a Model so there's no better place for it :)
It seems that each component that creates its own instance of [a] service. I don't understand why.
I note this AngularJs 2 - multiple instance of service created, but I'm not clear on the correct solution. Do I create the service instance _myService in main:
void main() {
bootstrap(AppComponent,[MyService]);
}
and then copy it to [child] components (because I also remove MyService from the component providers)? This doesn't seem correct, because the components reference _myService before it's instantiated, and I have to check it for being null.
Thanks
Steve
You can use factory constructor pattern like here.
Creating your service in the bootstrap will make sure there is only one instance of it for the app (if you don't provide it again in some component).
You get multiple copies of it only if you provide it in some #Component - then each instance of the component (and all its children) will have a separate instance of the service.
I'm learning prism V4 using MEF to load my modules. Loading modules does work, but in one module I want to load a View/ViewModel (MVVM) and don't really know how I get MEF to resolve all this stuff for me.
First: how do I need to mark the ViewModel (I follow the StockTraderRI example) so it is not loaded on startup but instead can be loaded during runtime into a region?
Second: how do I load the ViewModel using MEF so it gets connected to the corresponding interfaces?
MEF does this very nicely for things on startup which are marked as [Export], but I got no idea how to achieve this during runtime.
You can use what is known as a Lazy Export so that the interface is not resolved until you explicitly use it.
If you need to create multiple instances, MEF doesn't support this particularly well. You can either do your own discovery and instantiation, or you can define the Export like this:
[PartCreationPolicy(CreationPolicy.NonShared)]
[Export(typeof(ISomething)]
public class Something : ISomething { }
The downside is that now wherever you need to create the instance, you need to have a reference to the actual Container instance. Then you can do:
var something = _container.GetExportedObject<ISomething>();
EDIT: Okay, I think I understand better what you're after. Here is how I've typically resolved this issue:
I implement my View objects as UserControl instances and don't set a DataContext anywhere in their code or XAML.
I create a DataTemplate that binds from the Type of the ViewModel to the UserControl.
On my MainViewModel (or whatever corresponds to the View hosting the regions), I expose a general RegionX Object (possibly typed to an interface if all of my ViewModels will share some common functionality, but Object works fine).
I create a ContentPresenter with Content bound to the RegionX property.
Now my MainViewModel can import different ViewModel instances corresponding to the types of ViewModels that might be hosted by the RegionX. When I want to switch the 'active' View in the region, I simply set RegionX to the corresponding ViewModel.
By my (likely meager) understanding, doing this in the middle of a method in your controller / presenter is considered bad practice, since it creates a dependency between StructureMap and your presenter:
void Override() {
ICommentForOverrideGetter comm = StructureMap.ObjectFactory.GetInstance<ICommentForOverrideGetter>();
since this dependancy should be injected into the presenter via the constructor, with your IoC container wiring it up. In this case though my code needs a fresh copy of ICommentForOverrideGetter every time this method runs. Is this an exception to the above best practice, or a case where I should re-think my architecture?
It is said that there is no problem in computer science which cannot be solved by one more level of indirection:
If you just don't want the dependency in your presenter, inject a factory interface, the real implementation could do new CommentForOverrideGetter or whatever.
Edit:
"I have no problem ignoring best practices when I think the complexity/benefit ratio is too high": Neither do I, but as I said in the comments, I don't like hard dependencies on IoC containers in code I want to unit test and presenters are such a case.
Depending on what your ICommentForOverrideGetter does, you could also use a simple CommentForOverrideGetter.CreateNew() but as you require a fresh instance per call, I'd suspect at least some kind of logic associated with the creation? Or is it a stateful "service"?
If you insist on doing service location in your method, you should at least inject the container into your controller, so that you can eliminate the static method call. Add a constructor parameter of type StructureMap.IContainer and store it in a field variable. StructureMap will inject the proper container. You can then call GetInstance() on that container, instead of ObjectFactory.