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Dependency Injection

Dependency Injection​

Creating an instance of clock in the constructor works but it can become cumbersome when your controller uses many services. To solve this problem we use dependency injection or inversion of control.

We will register the Clock service as a singleton in Startup.cs. In the ConfigureServices Method add the following code

services.AddSingleton<Clock, Clock>();

You may have to add the import

using Stackworx.Workshop.Services;

Now we can change our constructor too

public ClockController(Clock clock)
{
    this.clock = clock;
}

Restart the application and everything should continue to work as expected

Adding an Interface​

This is not very useful on its own. More often we generate interfaces for our services so that we can hide the implementation details.

Right click on the project and add an new item. This time select Interface. Name it IClock.cs. Change our clock to implement this interface and give it a single interface method

class Clock : IClock

public interface IClock
{
    DateTime Now(bool utc);
}

You will have to mark the Now() method as virtual

And finally change all references to Clock to IClock and update the service registration

services.AddSingleton<IClock, Clock>();

Restart the application and confirm everything works

References​