I'm using DataTemplates in a ViewModel first approach.
I need to share a singleton ViewModel with multiple views.
So, I setup a simple ViewModel for each view and, using Ninject, I'm getting from the Kernel a reference to the singleton viewmodel...so I thought.
Structure:
MainViewModel
ObservableCollection TabViewModels {get; set;}
TabViewModels.Add(new View1ViewModel());
View1ViewModel
in constructor...getting reference to MainViewModel (singleton)
This causes a circular reference...the constructor in MainViewModel is executing each time around the circle.
I'm binding the viewmodel in Ninject this way...
Bind<GridViewModel>().ToSelf().InSingletonScope();
I'm getting the reference this way...
private MainViewModel _mvm;
public View1ViewModel()
{
_mvm = ViewModelLocator.MainViewModel;
//or
_mvm = ViewModelLocator.Kernel.Get<MainViewModel();
//both produce the same results
}
Related
I just tested out Dagger 2 and I am having some strange behaviour regarding the singleton annotation. I created some test code to show my problem.
My Module:
#Module
public class App {
#Provides
#Singleton
ThingA provideThingA(){
return new ConcreteThingA();
}
}
Interface of the thing I want in singleton:
public interface ThingA {
void showMyId();
}
Implementation:
public class ConcreteThingA implements ThingA {
#Override
public void showMyId() {
System.out.println(this);
}
}
Code that executes Dagger:
public void doStuff() {
ThingA thingA=DaggerThingAComponent.create().provideThingA();
ThingA thingB=DaggerThingAComponent.create().provideThingA();
System.out.println("Hello");
}
And here is a screenshot showing that I do not get the same instance when I ask for it twice. Have I missed something fundamental? ThingA is just a silly name and in my actual application I would like to have this singleton behaviour on my services.
The trick is that Dagger enforces scope/lifecycle through components, and you've created two separate components here:
ThingA thingA = DaggerThingAComponent.create().provideThingA();
ThingA thingB = DaggerThingAComponent.create().provideThingA();
Each time you create the new top-level #Singleton-annotated Component, Dagger creates a brand new object graph with a brand new container for each #Singleton object. You should have this instead:
ThingAComponent component = DaggerThingAComponent.create();
ThingA thingA = component.provideThingA();
ThingA thingB = component.provideThingA(); // thingA == thingB
Of course, anything further accessed through the dependency graph all comes from the same component, so this will preserve the singleton behavior you're looking for.
In most cases, you should not need to pass around the Component: The Component should be used for top-level components, and anything accessible through the injector should #Inject its dependencies (which means it shouldn't need a reference to the component itself). This might appear problematic during the migration to DI or Dagger, but creating multiple #Singleton components is not the way around it. Instead, try one of the following:
If you need multiple instances of something, you can always inject Provider<T> instead of T whether or not you've created a #Provides method. For that matter, you can inject a Lazy<T> if you only need zero or one copies of a particular dependency, particularly if the creation of that object is particularly heavy.
You can #Inject the component itself if you need it deep within the object graph, though it's always preferable to #Inject Provider<T> tProvider instead of #Inject YourComponent just to call YourComponent.getT.
In some cases, including Android, it may make sense to save the component to a globally-accessible field, either as an instance field in your Application or as a static field somewhere else. This is specifically because Android creates objects on its own, reflectively, rather than getting injected instances from the graph. For all other cases, inject your dependencies to avoid needing to pass around the component.
See also: Bindings in the graph from the Dagger 2 Users Guide
I am using the following Ninject related nuget packages in an MVC 5 WebAPI application:
Ninject.MVC5
Ninject.Extensions.Factory
ninject.extensions.conventions
I have a simple repository and a corresponding factory class like so:
public interface ITaskRunner
{
void Run();
}
public interface IRepository<T> where T: class
{
T[] GetAll();
}
public interface IRepositoryFactory<T> where T: class
{
IRepository<T> CreateRepository();
}
I have setup the Ninject bindings using ToFactory() from Ninject.Extensions.Factory like so:
kernel.Bind<ITaskRunner>().To<TaskRunner>().InSingletonScope();
kernel.Bind(typeof(IRepository<>)).To(typeof(Repository<>)).InRequestScope();
kernel.Bind<IRepositoryFactory<Contact>>().ToFactory();
I am using the factory in the following class:
public class TaskRunner : ITaskRunner
{
//MyTask is a simple POCO class(not shown for brevity)
IRepositoryFactory<MyTask> repoFactory = null;
IRepository<MyTask> repo = null;
public TaskRunner(IRepositoryFactory<MyTask> repoFactory)
{
this.repoFactory = repoFactory;
repo = repoFactory.CreateRepository();
}
//implementation elided
}
I am noticing that the call to repoFactory.CreateRepository() always returns the same instance of the factory (dynamic proxy) that Ninject generates.
Question : Is there a way to change/control this behavior and set a "lifetime" such as Transient, PerThread etc. for the instance that "CreateRepository" returns?
In this particular case, tasks might be processed asynchronously on multiple threads and the repository is not thread safe and hence singleton behavior for the instance returned from "CreateRepository" is not desirable.
I'm not sure what you are trying to achieve, but results you are seeing are quite expected because your TaskRunner is bound as Singleton (so constructed once), and you retrieve your repository in the TaskRunner constructor, which again happens once, and so repo is always the same instance. Note this happens regardless of how you bind IRepository and IRepositoryFactory, see Captive Dependency post by Mark Seemann for details http://blog.ploeh.dk/2014/06/02/captive-dependency/.
In fact, if you need to create repo in the constructor, you could just inject IRepository itself. The power of the Factory extension lies in the fact that it allows to resolve instances at runtime, not construction time. For example, if your TaskRunner has Run() method, you can create repository in it, so each task to run can have its own instance.
i am new in MVC and learning. here i am putting some code. so see first
public class HomeController : BaseController
{
private IProductRepository productRepository;
private string strRouteValue;
protected override void Initialize(System.Web.Routing.RequestContext requestContext)
{
base.Initialize(requestContext);
strRouteValue = this.ControllerContext.RouteData.Values["method"].ToString();
this.productRepository = Factory.Create(strRouteValue);
}
[HttpGet]
public ActionResult Index(int id)
{
productRepository.Get(id);
return View();
}
[HttpPost]
public ActionResult Index(Product model)
{
productRepository.Add(model);
return View();
}
}
what Initialize function does ?
every one must say this is where people would init many object, if so then we can do it in constructor of controller too. so what is special about controller Initialize function ?
what is difference between controller Initialize function and controller constructor ?
Check the documentation for that method: MSDN: Controller.Initialize():
Initializes data that might not be available when the constructor is called.
This method cannot be called directly. Override this method in order to provide additional processing tasks before any ActionResult methods are called, such as setting the thread culture or assigning a custom provider for TempData objects. If you override this method, call the base control's Initialize method.
And as I suggested on your previous twenty or so questions about MVC, Dependency Injection and controller instantiation: stop piecing together advice from poor blogposts and irrelevant answers on SO. Buy a decent MVC book and read it from cover to cover. Then do the same with a book about Unit Testing. You will never get a thorough understanding of things if you continue this way.
There is a difference between instantiating a controller and initializing it. Instantiating is moreover a .NET concept not MVC, so every class is automatically instantiated using default constructor. So, constructor is basically a concept of class whereas Initializing is concept of action method. We override Initialize() method in order to provide additional processing tasks before any ActionResult methods are called, such as setting the thread culture or assigning TempData objects etc....
I'm trying out Unity and I'm having problems declaring my viewmodel in XAML. Can you help me out?
XAML:
<UserControl.DataContext>
<search:SearchBoxViewModel />
</UserControl.DataContext>
Constructor:
[ImportingConstructor]
public SearchBoxViewModel(IRegionManager regionManager, IEventAggregator eventAggregator)
{
this.regionManager = regionManager;
this.eventAggregator = eventAggregator;
}
When I try to execute I get a resolutionfailedexception.
This worked when the viewmodel had an empty constructor. It seems as if it's having problems with the constructor injection.
If I load the module like this:
var searchView = Container.Resolve<SearchBoxView>();
searchView.DataContext = Container.Resolve<SearchBoxViewModel>();
//RegionManager.RegisterViewWithRegion(RegionNames.SearchRegion, typeof(SearchBoxView));
RegionManager.Regions[RegionNames.SearchRegion].Add(searchView);
It works.
Is there any possibility to do this with xaml ( with I personally think is better )?
By the way: I'm creating an application with wpf that primarily communicates with a webservice. What should I rather user: unity or MEF and what are the big differences between the two?
Thanks,
Raphi
http://msdn.microsoft.com/en-us/library/ms753379.aspx:
Requirements for a Custom Class as a XAML Element
In order to be able to be instantiated as an object element, your
class must meet the following requirements:
Your custom class must be public and support a default
(parameterless)
public constructor. (See following section for notes regarding
structures.)
...
So, if you want to use dependencies, you should right something like:
var searchView = Container.Resolve<SearchBoxView>();
public class SearchBoxView: UserControl
{
[Dependency]
public SearchBoxViewModel ViewModel
{
get { return (SearchBoxViewModel)DataContext; }
set { DataContext = value; }
}
I am developing a Windows Phone 7 app and am using the MVVM pattern. I have a need to pass a parameter to the contructor of the ViewModel for a page. All my datacontexts and binding are done in XAML. Through my research I've seen that I need to do so using a dependency injector such as NInject.
Here's a little detail on whats going on:
I have a page with a ListPicker that lists various tasks. Each task has a unique TaskID. When an item is selected I need to open another page that will show the selected Tasks detail. My ViewModel and binding is all done and works if I use a static TaskID in the ViewModel but of course I need to use a variable.
I've setup NInject in the project and the various classes needed such as ViewModelLocator and my NInjectModule as shown here:
public class LighthouseNInjectModule : NinjectModule
{
public override void Load()
{
this.Bind<TaskViewModel>().ToSelf().WithConstructorArgument("TaskID", 2690);
}
}
Note that I have hardcoded a TaskID here and using this code this value properly gets injected into my constructor. Of course, this is hardcoded and I need to get the TaskID for the selected ListPicker item. I know how to get the selected ID from the ListPicker but how do I make NInject aware of it so when my class constructor is run it will have the correct value?
Here is the basic definition of my ViewModel class showing use of the Injector attribute.
public class TaskViewModel : INotifyPropertyChanged
{
[Inject]
public TaskViewModel(int TaskID)
{
//run function to get data using TaskID
}
}
WithConstructorArgument has another oveload that accepts a lazy evaluated Func<Context, object>.