Using IHostingEnvironment in .NetCore library

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'

Unit Test projects are applications, not libraries. UnitTests must be targeting `netcoreapp1.x`, not `netstandard1.x" — Tseng, Dec 27 '16 at 10:34
I do according to this link `https://xunit.github.io/docs/getting-started-dotnet-core.html` — pmn, Dec 27 '16 at 11:47
That link also says `"netcoreapp1.0"` and this builds it as application, not class library. xunit doesn't work with `netstandard1.x` (which is what you get in project.json when you create a class library) — Tseng, Dec 27 '16 at 11:55
Yes exactly its an application, please see my update, i try another way, but it does not work too. — pmn, Dec 27 '16 at 12:13
I don't think you should register IHostingEnvironment with DI yourself it should already be there, it gets injected into the Startup constructor so it must already be in DI. I've been able to take a dependency on it in my class library projects with no issues. — Joe Audette, Dec 27 '16 at 12:23

score 12 · Accepted Answer · edited Jun 20 '20 at 09:12

12

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.

edited Jun 20 '20 at 09:12

Community

1
1

answered Dec 27 '16 at 12:28

Joel Harkes

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why `service.WebRootPath` give me null? – pmn Dec 27 '16 at 14:04
1

Because this is also later initialized: see `HostingEnvironmentExtensions.Initialize(...)` in namespace `Microsoft.AspNetCore.Hosting.Internal`. It is called on `WebHostBuilder.Build()` => `private this,BuildCommonSerivces()` => `Initialize()` – Joel Harkes Dec 27 '16 at 14:20
Im going wrong? Do u have suggestion that how can i getwebRootPath? – pmn Dec 27 '16 at 16:26
Instead of making your class library dependent on Hosting nuget package. give your class library its own [Options](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration#using-options-and-configuration-objects), and configure the options in your startup project. – Joel Harkes Dec 28 '16 at 08:22

score 5 · Answer 2 · answered Jun 08 '18 at 12:30

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

score 4 · Answer 3 · answered Aug 08 '20 at 20:36

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>();

score 2 · Answer 4 · answered Mar 17 '19 at 02:57

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.

score 0 · Answer 5 · answered Jul 14 '20 at 10:48

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 ^_^

Using IHostingEnvironment in .NetCore library

5 Answers5

solution

Behind the scenes dotnet core (Hosting nuget package)

Linked