Where To Place Common Variables in ASP.NET Core - asp.net-core

Question

I'm starting a new ASP.NET project after a few years developing in MVC4, and I have a question regarding architecture.
At the top corner of each page, I will display details of the current logged in user.
In MVC4 I achieved something like this by creating a BaseController, which created an EF data connection, and set up some common variables that would be used on every page - CurrentUser being one of them.
Now that I'm using Core, this approach doesn't seem to work, and certainly isnt mockable.
What would be the correct way to achieve something like this via ASP.NET Core?
I need the same variables on every view, and certainly dont want to have to write the code in each controller action!

Answer 1

You can use View Components feature in asp.net core to implement that functionality.
//In your ConfigureServices method , add your services that will be injected whenever view component is instantiated
public void ConfigureServices(IServiceCollection services) {
services.AddSingleton<IUserRespository, UserRepository>();
}
//Now Create a view component
public class LoggedInUser : ViewComponent
{
private IUserRespository userRepository;
//Services can be injected using asp.net core DI container
public LoggedInUser(IUserRepository userRepository,SomeOtherService service)
{
//assign services to local variable for use later
this.userRepository = userRepository;
}
//This method can take any number of parameters and returns view
public async Task<IViewComponentResult> InvokeAsync(int param1,string param2,etc )
{
//get the logged in user data here using available services
var loggedInUserData = GetSomeData(context);
return View(loggedInUserData );
}
}
Create view file # View/Shared/Components/LoggedInUser/Default.cshtml.View can be strongly typed.
#model LoggedInUserModel
<div>
<!-- html here to render model -->
</div>
Now, since you use to display this data on every page , you need to apply _Layout.chstml to all your pages . In the _Layout.chstml , you can render view component defined above with any additional parameter you would like to pass as anonymous type.
#await Component.InvokeAsync("LoggedInUser", new { param1=value,param2=value,etc })
Testing the View Component:
var mockRepository = Mock of ICityRepository;
var viewComponent= new LoggedInUser(mockRepository);
ViewViewComponentResult result
= viewComponent.Invoke() as ViewViewComponentResult; //using Invoke here instead of InvokeAsnyc for simplicity
//Add your assertions now on result
Note :
It is also possible to decorate a controller with [ViewComponent(Name = "ComponentName")] attribute and define public IViewComponentResult Invoke()
or public IViewComponentResult InvokeAsync() to turn them in to hybrid controller - view component.