ANGULAR2 Dependency Injection--the use of injectors

First, the display injection device

  Injector = Reflectiveinjector.resolveandcreate ([Car, Engine, Tires]);  Let car = injector.get (car);

Second, a single case service

In the scope of an injector, the dependencies are singleton, because they share a service instance

Three, multi-example service

Angular di is a layered dependency injection system, which means that nested injectors can create their own service instances.

Iv. Role of @injectabled

Identifies a class that can be instantiated by an injector. Typically, when you attempt to instantiate a class that is not identified @Injectable() , the injector will give an error.

It is recommended for each service class to @Injectable() be added, including those that do not rely strictly and do not need it. Because:

• • Future-oriented: no need to remember to add dependencies later @Injectable() .

  • Consistency: All services follow the same rules and do not need to consider why one is missing somewhere.

Five, @Component, @Directive, @Pipe do not need to add adorners, because they are a subtype of @injectable.

ANGULAR2 Dependency Injection--the use of injectors