I just started working with dependency injection for the first time and I am using as Ninject 2.0 as my IoC container in an ASP.NET MVC 2 website and I'm hitting an activation error that I am not sure how to react to. I am sure it's simple so hopefully someone can point me in the right direction without too much thought.
I have a property on my class BaseController which takes an IWebsiteSettings and is flagged with the [Inject] attribute. In my StandardKernel I load a module with the following code:
public class WebModule : Module
{
public override void Load()
{
Bind<IWebsiteSettings>()
.ToProvider(new WebsiteSettingsProvider(WebConfigurationManager.AppSettings))
.InSingletonScope();
}
}
public class WebsiteSettingsProvider : Provider<WebsiteSettings>
{
private const string WebsiteNameKey = "Website.Name";
private const string ContactFormEmailSubjectKey = "ContactForm.EmailSubject";
private const string ProductImageDirectoryKey = "Products.ImageDirectory";
private const string UploadTempDirectoryKey = "Uploads.TempDirectory";
protected NameValueCollection Settings { get; set; }
public WebsiteSettingsProvider(NameValueCollection settings)
{
Settings = settings;
}
protected override WebsiteSettings CreateInstance(IContext context)
{
return new WebsiteSettings
{
WebsiteName = Settings[WebsiteNameKey] ?? string.Empty,
ContactFormEmailSubject = Settings[ContactFormEmailSubjectKey] ?? string.Empty,
ProductImageDirectory = Settings[ProductImageDirectoryKey] ?? string.Empty,
UploadsTemporaryDirectory = Settings[UploadTempDirectoryKey] ?? string.Empty
};
}
}
This is fairly straightforward- I'm trying to load some data from the web.config file and store it in a singleton object for use across my controllers. The call to Bind seems to function exactly as it should and the Settings property in my provider is correctly initialized with the AppSettings collection in the config file. Still, when the application loads the first time:
Server Error in '/' Application.
Error activating SByte* using implicit self-binding of SByte*
No constructor was available to create an instance of the implementation type.
Activation path:
4) Injection of dependency SByte* into parameter value of constructor of type string
3) Injection of dependency string into property WebsiteName of type WebsiteSettings
2) Injection of dependency IWebsiteSettings into property WebsiteSettings of type HomeController
1) Request for HomeController
Suggestions:
1) Ensure that the implementation type has a public constructor.
2) If you have implemented the Singleton pattern, use a binding with InSingletonScope() instead.
Interestingly, if I refresh the page I don't get the exception and a call to Kernel.Get() returns the correct object.
Any advice?
(We talked about this on IRC, but I'm putting it here in case someone else runs into this problem as well.)
WebsiteSettings has [Inject] attributes on its properties, so Ninject is trying to resolve a binding from System.String to inject a value into the properties. Since you're using a custom provider to activate WebsiteSettings instances, you don't need [Inject] attributes on its properties.
The offending code was actually in the class WebsiteSettings where I was doing this:
public class WebsiteSettings : IWebsiteSettings
{
[Ninject.Inject]
public string WebsiteName
{
get; set;
}
[Ninject.Inject]
public string UploadsTemporaryDirectory
{
get; set;
}
[Ninject.Inject]
public string ContactFormEmailSubject
{
get; set;
}
[Ninject.Inject]
public string ProductImageDirectory
{
get; set;
}
}
By placing the Inject attribute on my properties I was causing Ninject to try to assign values that I never bound. Because I am using a Provider to load my type I do not need to include the Inject attribute.
Related
I have a class that implements the IValidatableObject interface, in order to validate the incoming data introduced by the user. The problem is that in order to validate that data, I need to use a class that implements the data repository pattern, which is in another assembly. Something like this:
public class SelectedFilteringCriteria : IValidatableObject
{
private IFiltersRepository _filtersRepository;
public SelectedFilteringCriteria(IFiltersRepository filtersRepository)
{
_filtersRepository = filtersRepository;
}
public int? SelectedValue { get; set; }
public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
var results = new List<ValidationResult>();
var valueOk = _filtersRepository.GetFilters().Any(
filter => filter.Value == SelectedValue
);
if (!valueOk)
{
results.Add(new ValidationResult("Not good :("));
}
return results;
}
}
The dependency container I'm using is Ninject. I would like to know if there's a way to tell MVC to inject the repository class into the IValidatableObject when it's going to be created.
Nope, it seems it's not possible because the MutableObjectModelBinder class, which is the one MVC 5 uses to create the corresponding object (SelectedFilteringCriteria in my case) from the action parameters, uses System.Activator instead of resolving the dependencies SelectedFilteringCriteria could have using the current DependencyResolver.
A workaround for this could be to do this inside the constructor of SelectedFilteringCriteria:
public SelectedFilteringCriteria()
{
_filtersRepository = DependencyResolver.Current.GetService<IFiltersRepository>();
}
But that could drive to the Service Locator Antipattern. Your choice.
I have created the following type in my MVC 6 application:
public class EncryptedType
{
...
}
I have a controller method as follows:
public IActionResult Index(EncryptedType id)
{
...
}
So given the the url would be something like:
http://localhost/Area1/Controller1/Index/fgf23237dsd
Where the EncryptedType class can handle converting to/from a string.
Currently the id is defaulting to the parameterless constructor value. What do I need to do to make this automatically convert the string id on the url to an instance?
Naturally I could use a string but I just feel having an explicit type to represent the type in the method is more explicit.
This should work out of the box.
For example, if this is EncryptedType:
public class EncryptedType
{
public string Id {get; set;}
public string Name {get; set;}
}
Then, if your query string looks something like this:
http://localhost:5000/Index?Id=1&Name=MyName
The data from the query string will be parsed automatically to an instance of this class.
It is not possible to instansiate the class with an other constructor than the default one.
Please look at the docs:
https://learn.microsoft.com/en-us/aspnet/core/mvc/models/model-binding
There is a section there that states the following:
In order for binding to happen the class must have a public default
constructor and member to be bound must be public writable properties.
When model binding happens the class will only be instantiated using
the public default constructor, then the properties can be set.
OK, I guess today I have my googling head on, so was able to work through a number of Stack Overflows and Microsoft docs. There are essentially 4 parts to wire up. These are:
IModelBinder implementation
IModelBinderProvider implementation
Mvc Service Registration Options
Attribute on the Controller Action
IModelBinder implementation
using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.ModelBinding;
public class EncryptedTypeModelBinder : IModelBinder
{
public Task BindModelAsync(ModelBindingContext bindingContext)
{
if (bindingContext == null)
{
throw new ArgumentNullException(nameof(bindingContext));
}
if (bindingContext.ModelType == typeof(EncryptedType))
{
EncryptedType decodedEncryptedTypeParameter;
ValueProviderResult value = bindingContext.ValueProvider.GetValue(bindingContext.FieldName);
string theStringToConvertToEncryptedType = value.FirstValue;
// add the custom convert from string to your type here, and set on the bindingContext.Result. We still return
// this value from the method wrapped in a Task.
if (EncryptedType.TryParse(theStringToConvertToEncryptedType, out decodedEncryptedTypeParameter))
{
bindingContext.Result = ModelBindingResult.Success(decodedEncryptedTypeParameter);
}
else
{
bindingContext.Result = ModelBindingResult.Failed();
}
return Task.FromResult(bindingContext.Result);
}
return Task.FromResult(ModelBindingResult.Failed());
}
}
IModelBinderProvider implementation
using Microsoft.AspNetCore.Mvc.ModelBinding;
public class EncryptedTypeModelBinderProvider : IModelBinderProvider
{
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
return new EncryptedTypeModelBinder();
}
}
Mvc Service Registration Options
services.AddMvc().AddMvcOptions(a =>
a.ModelBinderProviders.Add(new EncryptedTypeModelBinderProvider()));
Attribute on the Controller Action
public IActionResult Index(
[ModelBinder(BinderType = typeof(EncryptedTypeModelBinder))] EncryptedType id)
I have a vNext console application where one of my classes takes the OptionsModel<T> POCO configuration settings class.
I am unable to get the POCO settings class resolved and injected into my RabbitMqConnection class below.
Setting up the ServiceProvider is not the issue, it's the resolution of the settings class.
Note, this is a vNext console application (not an mvc6 app).
My second question is, and I understand constructor arguments should be kept minimal, but is it not best to pass the two strings as constructor arguments rather than an IOptions class as the former method is more descriptive of what the RabbitMqConnection class requires? If so, how is this best injected from the class that defined the mappings (Program.cs file in example below)
public class RabbitMqConnection
{
public string HostName { get; set; }
public string UserName { get; set; }
public RabbitMqConnection(IOptions<MessagingSettings> settings)
{
HostName = settings.Value.HostName;
UserName = settings.Value.UserName;
}
}
public class MessagingSettings
{
public string HostName { get; set; }
public string UserName { get; set; }
}
appsettings.json
{
"MessagingSettings":{
"HostName":"localhost",
"Username":"guest"
}
}
public void ConfigureServices(IServiceCollection services)
{
// tried registration a number of ways as below
services.Configure<MessagingSettings>(Configuration.GetSection("MessagingSettings"));
services.Configure<MessagingSettings>(Configuration);
// attempt 1 - get runtime error saying cant resolve IOptions<MessageSettings>
services.TryAdd(ServiceDescriptor.Singleton<RabbitMqConnection, RabbitMqConnection>());
// attempt 2 - same as above, when i breakpoint on messagingSettings, all the values in the object are null
services.TryAdd(ServiceDescriptor.Singleton<RabbitMqConnection>(factory =>
{
// instead of injecting the MessageSettings, pass through the string values (constructor omitted for clarity)
var messagingSettings = Configuration.Get<MessagingSettings>();
return new RabbitMqConnection(messagingSettings.HostName, messagingSettings.UserName);
}));
}
var conn = ServiceProvider.GetRequiredService<RabbitMqConnection>();
You need to call services.AddOptions()
I am using the MvcContrib library with Castle Windsor and I am having a problem
with setting a parameter when I register a component.
I have the following interfaces for classes that wrap a DataContext. I want
to be able to specify which DataContext to use for different services because
I am connecting to several databases to retrieve data.
public interface IDataContext
{
DataContext Context { get; }
}
public interface IReportingDC : IDataContext
{
}
public class Repository<T> : IRepository<T> where T : class
{
public IDataContext DC { get; set; }
public Repository(IDataContext dataContext)
{
DC = dataContext;
}
}
Here are the registration lines from my global.asax.cs.
container.AddComponentLifeStyle<IDataContext, MainDataContext>(Castle.Core.LifestyleType.PerWebRequest);
container.AddComponentLifeStyle<IReportingDC, ReportingDC>(Castle.Core.LifestyleType.PerWebRequest);
container.Register(Component.For<IRepository<ReportingTotals>>()
.ImplementedBy<Repository<ReportingTotals>>()
.Parameters(Parameter.ForKey("dataContext").Eq("IReportingDC"))
.LifeStyle.PerWebRequest
);
When I try and load the page I get the following error.
"Key invalid for parameter dataContext. Thus the kernel was unable to
override the service dependency"
Name your component and use ServiceOverrides instead of Parameters:
Component.For<IReportingDC>()
.ImplementedBy<ReportingDC>()
.Named("IReporting")
.LifeStyle.PerWebRequest
and
Component.For<IRepository<ReportingTotals>>()
.ImplementedBy<Repository<ReportingTotals>>()
.ServiceOverrides(ServiceOverride.ForKey("dataContext").Eq("IReporting"))
See the fluent API docs for reference.
I'm a newbie when it comes to DI and ninject and I'm struggling a bit
about when the actual injection should happen and how to start the
binding.
I'm using it already in my web application and it working fine there,
but now I want to use injection in a class library.
Say I have a class like this:
public class TestClass
{
[Inject]
public IRoleRepository RoleRepository { get; set; }
[Inject]
public ISiteRepository SiteRepository { get; set; }
[Inject]
public IUserRepository UserRepository { get; set; }
private readonly string _fileName;
public TestClass(string fileName)
{
_fileName = fileName;
}
public void ImportData()
{
var user = UserRepository.GetByUserName("myname");
var role = RoleRepository.GetByRoleName("myname");
var site = SiteRepository.GetByID(15);
// Use file etc
}
}
I want to use property injection here because I need to pass in a
filename in my constructor. Am I correct in saying that if I need to
pass in a constructor parameter, I cannot use constructor injection?
If I can use constructor injection with additional parameters, how do
I pass those parameters in?
I have a console app that consumes by Test class that looks as
follows:
class Program
{
static void Main(string[] args)
{
// NinjectRepositoryModule Binds my IRoleRepository etc to concrete
// types and works fine as I'm using it in my web app without any
// problems
IKernel kernel = new StandardKernel(new NinjectRepositoryModule());
var test = new TestClass("filename");
test.ImportData();
}
}
My problem is that when I call test.ImportData() my repositories are null - nothing has been injected into them. I have tried creating another module and calling
Bind<TestClass>().ToSelf();
as I thought this might resolve all injection properties in TestClass but I'm getting nowhere.
I'm sure this is a trivial problem, but I just can't seem to find out
how to go about this.
You are directly newing TestClass, which Ninject has no way of intercepting - remember there's no magic like code transformation intercepting your news etc.
You should be doing kernel.Get<TestClass> instead.
Failing that, you can inject it after you new it with a kernel.Inject( test);
I think there's an article in the wiki that talks about Inject vs Get etc.
Note that in general, direct Get or Inject calls are a Doing It Wrong smell of Service Location, which is an antipattern. In the case of your web app, the NinjectHttpModule and PageBase are the hook that intercepts object creation - there are similar interceptors / logical places to intercept in other styles of app.
Re your Bind<TestClass>().ToSelf(), generally a StandardKernel has ImplicitSelfBinding = true which would make that unnecessary (unless you want to influence its Scope to be something other than .InTransientScope()).
A final style point:- you're using property injection. There are rarely good reasons for this, so you should be using constructor injection instead.
And do go buy Dependency Injection in .NET by #Mark Seemann, who has stacks of excellent posts around here which cover lots of important but subtle considerations in and around the Dependency Injection area.
OK,
I've found out how to do what I need, thanks in part to your comments Ruben. I've created a new module that basically holds the configuration that I use in the class library. Within this module I can either Bind using a placeholder Interface or I can add a constructor parameter to the CustomerLoader.
Below is the code from a dummy console app to demonstrating both ways.
This might help someone else getting started with Ninject!
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Ninject.Core;
using Ninject.Core.Behavior;
namespace NinjectTest
{
public class Program
{
public static void Main(string[] args)
{
var kernel = new StandardKernel(new RepositoryModule(), new ProgramModule());
var loader = kernel.Get<CustomerLoader>();
loader.LoadCustomer();
Console.ReadKey();
}
}
public class ProgramModule : StandardModule
{
public override void Load()
{
// To get ninject to add the constructor parameter uncomment the line below
//Bind<CustomerLoader>().ToSelf().WithArgument("fileName", "string argument file name");
Bind<LiveFileName>().To<LiveFileName>();
}
}
public class RepositoryModule : StandardModule
{
public override void Load()
{
Bind<ICustomerRepository>().To<CustomerRepository>().Using<SingletonBehavior>();
}
}
public interface IFileNameContainer
{
string FileName { get; }
}
public class LiveFileName : IFileNameContainer
{
public string FileName
{
get { return "live file name"; }
}
}
public class CustomerLoader
{
[Inject]
public ICustomerRepository CustomerRepository { get; set; }
private string _fileName;
// To get ninject to add the constructor parameter uncomment the line below
//public CustomerLoader(string fileName)
//{
// _fileName = fileName;
//}
public CustomerLoader(IFileNameContainer fileNameContainer)
{
_fileName = fileNameContainer.FileName;
}
public void LoadCustomer()
{
Customer c = CustomerRepository.GetCustomer();
Console.WriteLine(string.Format("Name:{0}\nAge:{1}\nFile name is:{2}", c.Name, c.Age, _fileName));
}
}
public interface ICustomerRepository
{
Customer GetCustomer();
}
public class CustomerRepository : ICustomerRepository
{
public Customer GetCustomer()
{
return new Customer() { Name = "Ciaran", Age = 29 };
}
}
public class Customer
{
public string Name { get; set; }
public int Age { get; set; }
}
}