Lifetime Managers in Unity Container

The unity container manages the lifetime of objects of all the dependencies that it resolves using lifetime managers.

Unity container includes different lifetime managers for different purposes. You can specify lifetime manager in RegisterType() method at the time of registering type-mapping. For example, the following code snippet shows registering a type-mapping with TransientLifetimeManager.

var container = new UnityContainer()
                   .RegisterType<ICar, BMW>(new TransientLifetimeManager());

The following table lists all the lifetime managers:

Let’s understand each lifetime manager using the following example classes.

public interface ICar
{
    int Run();
}

public class BMW : ICar
{
    private int _miles = 0;

    public int Run()
    {
        return ++_miles;
    }
}

public class Ford : ICar
{
    private int _miles = 0;
    public int Run()
    {
        return ++_miles;
    }
}

public class Audi : ICar
{
    private int _miles = 0;

    public int Run()
    {
        return ++_miles;
    }
}

public class Driver
{
    private ICar _car = null;

    public Driver(ICar car)
    {
        _car = car;
    }

    public void RunCar()
    {
        Console.WriteLine("Running {0} - {1} mile ", 
                                      _car.GetType().Name, _car.Run());
    }
}

TransientLifetimeManager

TransientLifetimeManager is the default lifetime manager. It creates a new object of requested type every time you call Resolve() or ResolveAll() method.

var container = new UnityContainer()
                   .RegisterType<ICar, BMW>();

var driver1 = container.Resolve<Driver>();
driver1.RunCar();

var driver2 = container.Resolve<Driver>();
driver2.RunCar();

Output:

Running BMW – 1 Mile
Running BMW – 1 Mile

In the above example, unity container will create two new instances of BMW class and injects into driver1 and driver2 object. This is because the default lifetime manager is TransientLifetimeManager which creates new dependent object every time you call Resolve or ResolveAll method. You can specify the lifetime manager at the time of registering type using RegisterType() method.

The following example will display same output as above example because TransientLifetimeManager is the default manager if not specified.

var container = new UnityContainer()
                   .RegisterType<ICar, BMW>(
                             new TransientLifetimeManager());

var driver1 = container.Resolve<Driver>();
driver1.RunCar();

var driver2 = container.Resolve<Driver>();
driver2.RunCar();

Output:

Running BMW – 1 Mile
Running BMW – 1 Mile

ContainerControlledLifetimeManager

Use ContainerControlledLifetimeManager when you want to create a singleton instance.

var container = new UnityContainer()
                   .RegisterType<ICar, BMW>(new 
                            ContainerControlledLifetimeManager());

var driver1 = container.Resolve<Driver>();
driver1.RunCar();

var driver2 = container.Resolve<Driver>();
driver2.RunCar();

Output:

Running BMW – 1 mile
Running BMW – 2 mile

In the above example, we specified ContainerControlledLifetimeManager in RegisterType() method. So unity container will create a single instance of BMW class and inject it in all the instances of Driver.

HierarchicalLifetimeManager

The HierarchicalLifetimeManager is the same as ContainerControlledLifetimeManager except that if you create a child container then it will create its own singleton instance of registered type and will not share instance with parent container.

var container = new UnityContainer()
                   .RegisterType<ICar, BMW>(
                            new HierarchicalLifetimeManager());

var childContainer = container.CreateChildContainer();
            
var driver1 = container.Resolve<Driver>();
driver1.RunCar();

var driver2 = container.Resolve<Driver>();
driver2.RunCar();

var driver3 = childContainer.Resolve<Driver>();
driver3.RunCar();

var driver4 = childContainer.Resolve<Driver>();
driver4.RunCar();

Output:

Running BMW – 1 mile
Running BMW – 2 mile
Running BMW – 1 Mile
Running BMW – 2 Mile

As you can see, container and childContainer have their own singleton instance of BMW.

Visit Understand Lifetime Managers to learn more about it.