Dependency injection in OWIN
The DotvvmStartup class implements IDotvvmServiceConfigurator interface with the following method:
public void ConfigureServices(IDotvvmServiceCollection options)
{
options.Services.AddSingleton(...);
}
In this method, you can register any services in the IServiceCollection. You can register custom services using options.Services.AddTransient, options.Services.AddSingleton or options.Services.AddScoped.
The IServiceCollection uses the implementation from the Microsoft.Extensions.DependencyInjection library.
If you are fine with using this library, you can register all services in the ConfigureServices mentioned above. Then, everything will work as described in the Dependency injection chapter.
Custom viewmodel loader
If you are using a different dependency injection container, you'll want to resolve viewmodel dependencies using this container.
By default, when DotVVM needs to create a viewmodel, it looks in the IServiceCollection if the viewmodel is registered. If not, it then inspects its constructor and tries to obtain all the dependencies from the IServiceCollection.
This is done in the DefaultViewModelLoader class, which is a default implementation of the IViewModelLoader interface. If you need to plug a dependency injection container in, you can create a class that inherits DefaultViewModelLoader, and override the CreateViewModelInstance method.
Castle Windsor
Castle Windsor is one of the favorite DI containers in .NET.
Here is how to create the viewmodel loader using this container. Notice that we call container.Resolve in the CreateViewModelInstance, and container.Release in the DisposeViewModel.
using System;
using Castle.Windsor;
using DotVVM.Framework.ViewModel.Serialization;
namespace DotvvmDemo.Web
{
public class WindsorViewModelLoader : DefaultViewModelLoader
{
private readonly WindsorContainer container;
public WindsorViewModelLoader(WindsorContainer container)
{
this.container = container;
}
protected override object CreateViewModelInstance(Type viewModelType, IDotvvmRequestContext context)
{
return container.Resolve(viewModelType);
}
public override void DisposeViewModel(object instance)
{
container.Release(instance);
base.DisposeViewModel(instance);
}
}
}
The last thing is to replace the default viewmodel loader with the one you have just created. We should do this in the DotvvmStartup.cs class:
public void ConfigureServices(IDotvvmServiceCollection options)
{
// obtain the WindsorContainer instance from the place where you initialize it
var windsorContainer = ...
options.Services.AddSingleton<IViewModelLoader>(serviceProvider => new WindsorViewModelLoader(windsorContainer));
}
Other containers
If you use another container, the implementation will be very similar. Don't forget to tell the container to release the instances in the DisposeViewModel method. This method is called when the HTTP request ends and DotVVM no longer needs the viewmodel object.
Some containers do this by creating a "scope" in the CreateViewModelInstance method and disposing the scope in the DisposeViewModel method.
Static command services
If you are using a different dependency injection container, registering all components in IServiceCollection in DotvvmStartup can be problematic and can lead to registration of the same services in the two containers.
Instead, you might use a custom IStaticCommandServiceLoader to have your service instances resolved directly from your container.
using System;
using Castle.Windsor;
using DotVVM.Framework.ViewModel.Serialization;
namespace DotvvmDemo.Web
{
public class WindsorStaticCommandServiceLoader : DefaultStaticCommandServiceLoader
{
private readonly WindsorContainer container;
public WindsorStaticCommandServiceLoader(WindsorContainer container)
{
this.container = container;
}
public override object GetStaticCommandService(Type serviceType, IDotvvmRequestContext context)
{
return container.Resolve(serviceType);
}
}
}
To register the alternative loader, replace the default one using the following code in DotvvmStartup.cs:
public void ConfigureServices(IDotvvmServiceCollection services)
{
services.Services.AddSingleton<IStaticCommandServiceLoader>(serviceProvider => new WindsorStaticCommandServiceLoader(container));
}