在 .NetCore 库中使用 IHostingEnvironment

Question

I build an ASP.NET Core application and I create a .NET Core Class Library for unit testing.

I want to use IHostingEnvironment in my library (to get physical path of a file), so I've added this line to Startup.cs of my ASP.NET Core application :

services.AddSingleton<IHostingEnvironment>();

In the Library I've added reference to my ASP.NET application, and in my class I wrote this:

private IHostingEnvironment _env;
public Class1(IHostingEnvironment env)
{
    _env = env;
}

But when I run it then it gives me this error:

the following constructor parameters did not have matching fixture date : IHostingEnvironment env

What is the problem? How can I use it in .NET Core Class Library?

---

EDIT: I tried to use this too:

IServiceCollection services = new ServiceCollection();
services.AddSingleton<IHostingEnvironment>();
IServiceProvider provider = services.BuildServiceProvider();
IHostingEnvironment service = provider.GetService<IHostingEnvironment>();
var p = service.WebRootPath; 

The last one gives me this error:

Cannot instantiate implementation type 'Microsoft.AspNetCore.Hosting.IHostingEnvironment' for service type 'Microsoft.AspNetCore.Hosting.IHostingEnvironment'

Answer 1

Note: services.AddSingleton<IHostingEnvironment>(); means you are registering IHostingEnvironment as an implementation for IHostingEnvironment in a singleton scope (always reuse).

Since you can't create an instance of an interface, you get this error.

solution

define the class you want to be created (that implements IHostingEnvironment ), eg:

services.AddSingleton<IHostingEnvironment>(new HostingEnvironment());

Behind the scenes dotnet core (Hosting nuget package)

In the WebHostBuilder The first row in the constructor is:

this._hostingEnvironment = (IHostingEnvironment) new HostingEnvironment();

This hosting environment is later filled with more settings, by the webhost builder.

You should look at their github page or decompile the sources: https://github.com/aspnet/Hosting

Note: Most of the properties/settings of HostingEnvironment are set on Build() method of the WebHostBuilder . If you want to moq/test this yourself you should set these properties yourself or just also include the WebHostBuilder in your test.

Answer 2

For my .net class library all I had to do is install the following nuget package for version 2.1.0:

Microsoft.AspNetCore.Hosting.Abstractions

https://www.nuget.org/packages/Microsoft.AspNetCore.Hosting.Abstractions/

and then I just injected IHostingEnvironment into my constructor.

I didn't even need to modify Startup.cs

Answer 3

This worked for me in both .net core class library and console application:

Using references,

using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Hosting.Internal;

Adding DI registration,

services.AddSingleton<IHostingEnvironment, HostingEnvironment>();

Answer 4

A note for reference as I ended up here.

If you target netstandard (netstandard2.0) in your class library, add Microsoft.Extensions.Hosting.Abstractions from NuGet to get the IHostingEnvironment interface without any implementations.

I know question specifies .net core, anyways.. might help out those being where I were.

Answer 5

Try this, its simple enough

private IHostEnvironment env;
public Startup(IHostEnvironment env)
{
    this.env = env;
}
public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<IHostEnvironment>(env);
}

then you can use it in your class

private IHostingEnvironment _env;
public Class1(IHostingEnvironment env)
{
    _env = env;
}

hope it does the job ^_^