ctacke / MeadowDI

A test run on a DI container for Wilderness Labs Meadow

Meadow Dependency Injection

A test run on a DI container for Wilderness Labs Meadow

The ServiceCollection

The MeadowApp class contains a static ServiceCollection instance, which is a very simple, but still powerful Dependency Injection (DI) container.

The ServiceCollection supports:

• Singleton instance registration by type (class or interface)
• Resolving a contained instance by type (class or interface)
• Registering an existing type instance
• Registering a Type and the cotainer will auto-create it
• Simple constructor injection on creation
• Simple property injection on creation

Adding an instace that already exists

You can directly add an instance. It will be registered by direct type name:

var myObject = new Thing();
MeadowApp.Services.Add(myObject)

You can optionally register it as anything it derives from:

var myObject = new Thing(); // <-- implements IThing
MeadowApp.Services.Add<IThing>(myObject);

Automatic Instance Creation

You can have the DI container create an object for you (with injection) as follows:

var myObject = MeadowApp.Services.Create<Thing>()

You can optionally register it as anything it derives from:

var myObject = MeadowApp.Services.Create<Thing, IThing>(); <-- Thing implements IThing

Retrieving an Object

You simply resolve and retrieve by type:

var thing = MeadowApp.Services.Get<Thing>()

or

var thing = MeadowApp.Services.Get<IThing>()

Constructor Injection

If a constructor exists that has parameters that can be fulfilled by existing registered objects, that constructor will be called. The container will not cascade create objects, so if your contructor needs something that is not yet registered, it will fail.

Property Injection

Property injection happed after construction, but works similarly. If you have a public, settable property of a Type that is registered, the property will be set immediately after construction.

Types in the base implementation

The default DI Container starts with the global F7Micro Device object already registered, so if you create a service that needs that object, you can use injection to retrieve it.

Example

var myService = MeadowApp.Services.Create<ILedService>();

...

public LedService(F7Micro device)
{
    // F7Micro will get injected here
}