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Constructor Injection in Xamarin Froms .xaml.cs file classes

I want to take advantage of dependency injection in my Xamarin project but can't get constructor injection to work in C# classes behind XAML views. Is there any way to do it ?
I've seen guides how to setup dependency injections in View Models, to later use them as repositories but that doesn't work for me.
So far I tried Ninject and Unity.
Code:
This is the service I want to use inside of my PCL project:
public class MyService : IMyService
{
public void Add(string myNote)
{
//Add Note logic
}
}
Interface:
public interface IMyService
{
void Add(string myNote);
}
Unity setup in App.Xaml:
public App ()
{
InitializeComponent();
var unityContainer = new UnityContainer();
unityContainer.RegisterType<IMyService, MyService>();
var unityServiceLocator = new UnityServiceLocator(unityContainer);
ServiceLocator.SetLocatorProvider(() => unityServiceLocator);
MainPage = new MainMasterMenu(); //<-- feel that I'm missing something here as I shouldn't be creating class instances with DI, right ?
}
Usage that I'd like to see. This is .CS file behind a XAML starting page:
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class MainMasterMenu : MasterDetailPage
{
private IMyService _myService;
public MainMasterMenu(IMyService myService)
{
_myService = myService
}
private void SomeFormControlClickEvent(object sender, ItemChangedEventArgs e)
{
_myService.Add("hi");
}
}

For that simple example creating the MainMasterMenu directly would be no issue, but you would have to pass the reference to your service
MainPage = new MainMasterMenu(unityContainer.Resolve<IMyService>());
But this would mean that you'll have to change that line every time the constructor of MainMasterMenu changes. You could circumvent this by registering the MainMasterMenu, too.
unityContainer.RegisterType<MainMasterMenu>();
...
MainPage = unityContainer.Resolve<MainMasterPage>();
Anyway, anytime you want to navigate to another page, which needs any dependency registered with unity, you'll have to make sure to resolve its dependencies properly, which requires (at least indirect) access to the unity container. You could pass a wrapper that encapsules the access to unity
interface IPageResolver
{
T ResolvePage<T>()
where T : Page;
}
and then implement that resolver with unity
public class UnityPageResolver
{
private IUnityContainer unityContainer;
public UnityPageResolver(IUnityContainer unityContainer)
{
this.unityContainer = unityContainer;
}
public T ResolvePage<T>()
where T : Page // do we need this restriction here?
{
return unityContainer.Resolve<T>();
}
}
This gets registered with unity
unityContainer.RegisterInstance<IUnityContainer>(this);
unityContainer.RegisterType<IPageResolver, UnityPageResolver>();
But you should have a look at the Prism library (see here) that solves many of the issues (e.g. it provides an INavigationService that lets you navigate to other pages without caring about the dependencies and it provides facilities to resolve viewmodels automatically, including dependencies).

A proper MVVM-style way to add a Button to Toolbar from Prism module

I have composite application with toolbar and I want to make my modules possible to add some buttons to toolbar. As I have understood, a RegionManager should be used to provide this possibility.
I wrote a code like this:
public class MyModule : IModule
{
private readonly IUnityContainer _container;
public MyModule(IUnityContainer Container) { _container = Container; }
public void Initialize()
{
var regionManager = _container.Resolve<RegionManager>();
regionManager.RegisterViewWithRegion("MainToolbar",
() => new Button
{
Content = "My Button",
Command = new DelegateCommand(/* */)
});
}
}
But it seems like creating a buttons from code, especially inside of Module class is not a good idea, according the MVVM pattern. And the second problem is that the button is being created before other modules would be initialized, so I can't refer to services registred by other modules.
What exactly I'm doing wrong? What is a propper way to collect actions from multiple modules into one toolbar?

Your idea is correct, just swap out the button for a view that contains a button. Then make the toolbar a region and inject the "button"-view into the "toolbar"-region.
If your module depends on services that come from other modules, make your module dependent on those modules, so that prism makes sure that the services are initialized first:
[ModuleDependency("ServiceModule")]
public class ModuleA : IModule
{
...
}
public class ServiceModule : IModule
{
...
}

Re-implementing WindowManager using ModernUI + Caliburn.Micro combination

Here Caliburn.Micro was successfully combined with ModernUI.
But if we want to use multiple windows we also need to re-implement Caliburn's WindowManager to work properly with ModernUI. How can it be done?
UPDATE:
(Additional question about IoC-Container/Dependency Injection)
Ok, as I get it: I used a Constructor Injection here:
public class BuildingsViewModel : Conductor<IScreen>
{
public BuildingsViewModel(IWindowManager _windowManager)
{
windowManager = _windowManager;
}
}
As far as BuildingsViewModel resolved from IoC container,
container itself injected ModernWindowManager implementation of IWindowManager interface because of this line in Bootstrapper's Configure() method:
container.Singleton<IWindowManager, ModernWindowManager>();
If I resolving an object instance from container, it injects all needed dependencies. Like a tree.
1) So now I wonder how can I replace this line using an injection(with interface)?
_windowManager.ShowWindow(new PopupViewModel());
2) If I want my whole project match DI pattern, all objects instances must be injected into ModernWindowViewModel, that resolves from container first?
3) Is it okay to use Caliburn's SimpleContainer for whole project, or better use mature framework like Castle Windsor? Should I avoid mixing?
UPDATE2:
4) Integrating an IoC container into an existing application requires creating this container first(in Main() method of console app for example), and then all object instanses must grow from it with injected dependencies?

Simply create your own derived WindowManager and override EnsureWindow:
public class ModernWindowManager : WindowManager
{
protected override Window EnsureWindow(object rootModel, object view, bool isDialog)
{
var window = view as ModernWindow;
if (window == null)
{
window = new ModernWindow();
window.SetValue(View.IsGeneratedProperty, true);
}
return window;
}
}
Any views that you want to use as popups must be based on ModernWindow and must either use a LinkGroupCollection or you must set the ContentSource property of the window, otherwise there will be no content.
You could possibly make this View-First but it works ViewModel-First using the method above.
e.g. to popup my PopupView I did the following
PopupView.xaml
<mui:ModernWindow x:Class="TestModernUI.ViewModels.PopupView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mui="http://firstfloorsoftware.com/ModernUI"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300" ContentSource="/ViewModels/ChildView.xaml">
</mui:ModernWindow>
PopupViewModel.cs
public class PopupViewModel : Screen
{
// Blah
}
Code to popup the view from another ViewModel:
public void SomeMethod()
{
_windowManager.ShowWindow(new PopupViewModel()); // Or use injection etc
}
Don't forget to register ModernWindowManager in place of WindowManager in your container!
e.g. using CM's SimpleContainer
container.Singleton<IWindowManager, ModernWindowManager>();
Obviously the only downside I can see to the above is that you can't seem to put content directly in a ModernWindow, so you have to have two UserControls for every popup!
A workaround would be to change EnsureWindow in ModernWindowManager so that it created a UserControl based on ModernWindow and set the ContentSource to the URI of the view you want to load, this will trigger the content loader and wire up your ViewModel. I'll update if I get a minute to try it.
Update:
Ok, so at the moment it's very hacky, but this could be a starting point for something useful. Basically I'm generating a URI based on the namespace and name of the view.
I'm sure there is a more reliable way of doing this, but for my test project it works:
protected override Window EnsureWindow(object rootModel, object view, bool isDialog)
{
var window = view as ModernWindow;
if (window == null)
{
window = new ModernWindow();
// Get the namespace of the view control
var t = view.GetType();
var ns = t.Namespace;
// Subtract the project namespace from the start of the full namespace
ns = ns.Remove(0, 12);
// Replace the dots with slashes and add the view name and .xaml
ns = ns.Replace(".", "/") + "/" + t.Name + ".xaml";
// Set the content source to the Uri you've made
window.ContentSource = new Uri(ns, UriKind.Relative);
window.SetValue(View.IsGeneratedProperty, true);
}
return window;
}
My full namespace for my view was TestModernUI.ViewModels.PopupView and the URI generated was /ViewModels/PopupView.xaml which then was loaded and bound via the content loader automagically.
Update 2
FYI here is my Bootstrapper configure method:
protected override void Configure()
{
container = new SimpleContainer();
container.Singleton<IWindowManager, ModernWindowManager>();
container.Singleton<IEventAggregator, EventAggregator>();
container.PerRequest<ChildViewModel>();
container.PerRequest<ModernWindowViewModel>();
container.PerRequest<IShell, ModernWindowViewModel>();
}
Here I create the container, and register some types.
The CM services such as WindowManager and EventAggregator are both registered against their respective interfaces and as singletons so only 1 instance of each will be available at run time.
The view models are registered as PerRequest which creates a new instance every time you request one from the container - this way you can have the same window popup multiple times without strange behaviour!
These dependencies are injected into the constructor of any objects resolved at run time.
Update 3
In answer to your IoC questions:
1) So now I wonder how can I replace this line using an injection(with interface)? _windowManager.ShowWindow(new PopupViewModel());
Since your viewmodels will now usually need dependencies you need to have some way of injecting them into the instances. If PopupViewModel had several dependencies, you could inject them into the parent class but this would couple the parent viewmodel to PopupViewModel in some way.
There are a couple of other methods you can use to get an instance of PopupViewModel.
Inject it!
If you register PopupViewModel as PerRequest you will get a new instance of it every time you request it. If you only need one popup instance in your viewmodel you can just inject it:
public class MyViewModel
{
private PopupViewModel _popup;
private IWindowManager _windowManager;
public MyViewModel(PopupViewModel popup, IWindowManager windowManager)
{
_popup = popup;
_windowManager = windowManager;
}
public void ShowPopup()
{
_windowManager.ShowPopup(_popup);
}
}
The only downside is that the instance will be the same one if you need to use it multiple times in the same viewmodel, though you could inject multiple instances of PopupViewModel if you knew how many you needed at the same time
Use some form of on-demand injection
For dependencies which are required later on you can use on-demand injection such as a factory
I don't think Caliburn or SimpleContainer support factories out of the box, so the alternative is to use IoC.Get<T>. IoC is a static class which lets you access your DI container after instantiation
public void ShowPopup()
{
var popup = IoC.Get<PopupViewModel>();
_windowManager.ShowWindow(popup);
}
You need to make sure you have correctly registered the container in your bootstrapper and delegated any calls to CM's IoC methods to the container - IoC.Get<T> calls the bootstrapper's GetInstance and other methods:
Here's an example:
public class AppBootstrapper : BootstrapperBase {
SimpleContainer container;
public AppBootstrapper() {
Initialize();
}
protected override void Configure() {
container = new SimpleContainer();
container.Singleton<IWindowManager, ModernWindowManager>();
container.Singleton<IEventAggregator, EventAggregator>();
container.PerRequest<IShell, ModernWindowViewModel>();
// Register viewmodels etc here....
}
// IoC.Get<T> or IoC.GetInstance(Type type, string key) ....
protected override object GetInstance(Type service, string key) {
var instance = container.GetInstance(service, key);
if (instance != null)
return instance;
throw new InvalidOperationException("Could not locate any instances.");
}
// IoC.GetAll<T> or IoC.GetAllInstances(Type type) ....
protected override IEnumerable<object> GetAllInstances(Type service) {
return container.GetAllInstances(service);
}
// IoC.BuildUp(object obj) ....
protected override void BuildUp(object instance) {
container.BuildUp(instance);
}
protected override void OnStartup(object sender, System.Windows.StartupEventArgs e) {
DisplayRootViewFor<IShell>();
}
Castle.Windsor supports factories so that you can Resolve and Release your components and manage their lifetime more explicitly, but I won't go into that here
2) If I want my whole project match DI pattern, all objects instances must be injected into ModernWindowViewModel, that resolves from container first?
You only need to inject the dependencies that the ModernWindowViewModel needs. Anything that is required by children is automatically resolved and injected e.g.:
public class ParentViewModel
{
private ChildViewModel _child;
public ParentViewModel(ChildViewModel child)
{
_child = child;
}
}
public class ChildViewModel
{
private IWindowManager _windowManager;
private IEventAggregator _eventAggregator;
public ChildViewModel(IWindowManager windowManager, IEventAggregator eventAggregator)
{
_windowManager = windowManager;
_eventAggregator = eventAggregator;
}
}
In the above situation, if you resolve ParentViewModel from the container - the ChildViewModel will get all it's dependencies. You don't need to inject them into the parent.
3) Is it okay to use Caliburn's SimpleContainer for whole project, or better use mature framework like Castle Windsor? Should I avoid mixing?
You can mix, but it might be confusing as they won't work with each other (one container won't know about the other). Just stick with one container, and SimpleContainer is fine - Castle Windsor has a lot more features, but you might never need them (I've only used a few of the advanced features)
4) Integrating an IoC container into an existing application requires creating this container first(in Main() method of console app for example), and then all object instanses must grow from it with injected dependencies?
Yes, you create the container, then you resolve the root component (in 99.9% of applications there is one main component which is called the composition root), and this then builds the full tree.
Here is an example of a bootstrapper for a service based application. I'm using Castle Windsor and I wanted to be able to host the engine in a Windows service or in a WPF application or even in a Console Window (for testing/debug):
// The bootstrapper sets up the container/engine etc
public class Bootstrapper
{
// Castle Windsor Container
private readonly IWindsorContainer _container;
// Service for writing to logs
private readonly ILogService _logService;
// Bootstrap the service
public Bootstrapper()
{
_container = new WindsorContainer();
// Some Castle Windsor features:
// Add a subresolver for collections, we want all queues to be resolved generically
_container.Kernel.Resolver.AddSubResolver(new CollectionResolver(_container.Kernel));
// Add the typed factory facility and wcf facility
_container.AddFacility<TypedFactoryFacility>();
_container.AddFacility<WcfFacility>();
// Winsor uses Installers for registering components
// Install the core dependencies
_container.Install(FromAssembly.This());
// Windsor supports plugins by looking in directories for assemblies which is a nice feature - I use that here:
// Install any plugins from the plugins directory
_container.Install(FromAssembly.InDirectory(new AssemblyFilter("plugins", "*.dll")));
_logService = _container.Resolve<ILogService>();
}
/// <summary>
/// Gets the engine instance after initialisation or returns null if initialisation failed
/// </summary>
/// <returns>The active engine instance</returns>
public IIntegrationEngine GetEngine()
{
try
{
return _container.Resolve<IIntegrationEngine>();
}
catch (Exception ex)
{
_logService.Fatal(new Exception("The engine failed to initialise", ex));
}
return null;
}
// Get an instance of the container (for debugging)
public IWindsorContainer GetContainer()
{
return _container;
}
}
Once the bootstrapper is created, it sets up the container and registers all services and also plugin dlls. The call to GetEngine starts the application by resolving Engine from the container which creates the full dependency tree.
I did this so that it allows me to create a service or a console version of the application like this:
Service Code:
public partial class IntegrationService : ServiceBase
{
private readonly Bootstrapper _bootstrapper;
private IIntegrationEngine _engine;
public IntegrationService()
{
InitializeComponent();
_bootstrapper = new Bootstrapper();
}
protected override void OnStart(string[] args)
{
// Resolve the engine which resolves all dependencies
_engine = _bootstrapper.GetEngine();
if (_engine == null)
Stop();
else
_engine.Start();
}
protected override void OnStop()
{
if (_engine != null)
_engine.Stop();
}
}
Console App:
public class ConsoleAppExample
{
private readonly Bootstrapper _bootstrapper;
private IIntegrationEngine _engine;
public ConsoleAppExample()
{
_bootstrapper = new Bootstrapper();
// Resolve the engine which resolves all dependencies
_engine = _bootstrapper.GetEngine();
_engine.Start();
}
}
Here's part of the implementation of IIntegrationEngine
public class IntegrationEngine : IIntegrationEngine
{
private readonly IScheduler _scheduler;
private readonly ICommsService _commsService;
private readonly IEngineStateService _engineState;
private readonly IEnumerable<IEngineComponent> _components;
private readonly ConfigurationManager _configurationManager;
private readonly ILogService _logService;
public IntegrationEngine(ICommsService commsService, IEngineStateService engineState, IEnumerable<IEngineComponent> components,
ConfigurationManager configurationManager, ILogService logService)
{
_commsService = commsService;
_engineState = engineState;
_components = components;
_configurationManager = configurationManager;
_logService = logService;
// The comms service needs to be running all the time, so start that up
commsService.Start();
}
All of the other components have dependencies, but I don't inject those into the IntegrationEngine - they are handled by the container

Best practice for Ninject to get different implementations based on top level project

I am just starting to learn Dependency Injection and I am stuck here.
My project has a WCF DataService over an Entity Framework DbContext.
public class MyDataService : DataService<MyDbContext>
{
protected override MyDbContext CreateDataSource()
{
// I want to use dependency injection for this
return new MyDbContext();
}
}
The class is either
a) IIS hosted, so I don't have any control
b) for integration tests, created with var host = new DataServiceHost(type, new Uri[] { });
both use different contstructors for MyDbContext
So basically to inject the Context with this
protected override MyDbContext CreateDataSource()
{
INinjectModule module = ???; // -
IKernel kernel = new StandardKernel(module);
return kernel.Get<MyDbContext>();
}
So the question is, what is best practice in this situation?
Should I:
a) Create a Module in a Class Library that both main projects and the service use
b) Create a public static Variable inside the DataService project that holds the Ninject module.
c) Create a public static Variable inside the DataService project that holds the Ninject kernel
d) Something else.
I would prefer something like
protected override MyDbContext CreateDataSource()
{
DefaultKernel.Get<MyDbContext>();
}

Firstly, you should have a Composition Root. That is, a single place where your Kernel is created (not in every single function).
Secondly, you don't need a NinjectModule here.. you're asking Ninject to create an instance of a concrete object (which in almost all circumstances.. defeats the purpose).
What you should create, is a separate NinjectModule pass it into the constructor of the Kernel.. something like this:
interface IContext {
}
class MyDbContext : DbContext, IContext {
}
class YourModule : NinjectModule {
protected override void Bind() {
Bind<IContext>().To<MyDbContext>();
}
}
// In your composition root somewhere
var kernel = new StandardKernel(new NinjectModule[] { new YourModule() });
// in your createdatasource method
kernel.Get<IContext>();
This will get you started. Normally, your composition root is what drives injection of objects throughout your application, thereby eliminating the need to pass the Kernel around (which you will have to do in your current setup).
The hard thing to understand when starting out with DI/IoC is that it is the container's job to create your entire dependency graph. Therefore, if you setup the following bindings:
IContract1 -> ConcreteObject1
IContract2 -> ConcreteObject2
IContract3 -> ConcreteObject3
..and have the following setup:
class ConcreteObject1 : IContract1 {
public ConcreteObject1(IContract2 contract3) {
}
}
class ConcreteObject2 : IContract2 {
public ConcreteObject2(IContract3 contract3) {
}
}
If you ask your container for a concrete implementation of IContract1 (which will be ConcreteObject1), then it will create it.... BUT: ConcreteObject1 requires a concrete implementation of IContract2 in the constructor. So the container says "Wait, I know how to create this".. and passes in an instance of ConcreteObject2. Again, it says "wait, ConcreteObject2 wants a concrete implementation of IContract3.. again, it goes and fetches one.
Hopefully that helps.

Ninject + ASP.NET Web Forms Not Working

I've successfully implemented Ninject in an MVC3 application, but am running into some trouble doing the same thing with ASP.NET Web Forms. I'm getting null references every time I try to access an injected property in my business layer. After setting breakpoints within the CreateKernel method, as well as several places within the ServiceLocator class, it looks like none of them are ever getting hit, so it's not even loading.
I'm sure I'm just approaching this wrong, but there is very little documentation or info out there for wiring up Ninject in a Web Forms application.
Basically here's what I have so far:
code behind
public class ReviewManager
{
[Inject] private IReviewRepository _reviewRepository { get; set; }
public ReviewManager() { }
public ReviewManager(IReviewRepository reviewRepository)
{
_reviewRepository = reviewRepository;
}
public Review GetById(int id)
{
if (id <= 0) throw new ArgumentException("ID must be greater than zero");
**I get a null reference exception on the next line. _reviewRepository is null**
return _reviewRepository.GetById(id);
}
}
global.asax.cs
public class Global : NinjectHttpApplication
{
protected override IKernel CreateKernel()
{
return ServiceLocator.Kernel;
}
// deleted for brevity
}
ServiceLocator.cs (edited for brevity, the relevant parts are here)
public static class ServiceLocator
{
public static IKernel Kernel { get; set; }
public static ILogger Logger { get; set; }
static ServiceLocator()
{
Kernel = new StandardKernel(new INinjectModule[] {
new LoggerBindings(),
new DataBindings()
});
if (Logger == null)
Logger = Kernel.Get<ILogger>();
}
}
public class LoggerBindings : NinjectModule
{
public override void Load()
{
Bind<ILogger>().To<NLogLogger>();
}
}
public class DataBindings : NinjectModule
{
public override void Load()
{
Bind<IReviewRepository>().To<ReviewRepository>();
}
}

ASP.Net via WebForms does not allow you to manage the lifecycle of all object instances (like MVC does). For example, the framework instantiates page objects. This means you probably can't implement DI in quite the same way as you would in MVC/WPF/Silverlight (the same problem is present in WinForms IIRC). You will likely have to initiate the dependency graph directly in each of your code behinds.
Translation: you will want to call ServiceLocator.Kernel.Get<IReviewRepository> when your page loads (or as lazy-init on the property).

The cool thing about MVC ist that it can run side a side of ASP.NET WebForm pages in the same application. In my opinion the best way to extend ASP.NET WebForms websites is to create new pages using MVC3 and to refactor every page that needs major changes to MVC3.
If this is no option go and use the Ninject.Web extension. It contains a IHttpModule that property injects all web pages and controlls after they are initialized. That way you can property inject the services als have them created by Ninject.

A potential workaround, by changing your DataBindings class as follows:
public class DataBindings : NinjectModule
{
public override void Load()
{
Bind<IReviewRepository>().To<ReviewRepository>();
Bind<ReviewManager>().ToSelf();
}
}
And within your caller, instead of
var rm = new ReviewManager();
Try using
var rm = ServiceLocator.Kernel.Get<ReviewManager>();
I havent tested this code, but i think it'll solve your null reference problem.

I use property injection for pages, masterpages and usercontrols. All my pages, for example, inherit from a base class that overrides RequestActivation method with the following code:
''' <summary>
''' Asks the kernel to inject this instance.
''' </summary>
Protected Overridable Sub RequestActivation()
ServiceLocator.Kernel.Inject(Me)
End Sub
And in each page I declare injectable properties:
<Inject()>
Property repo As IMyRepository