Angular의 종속성 주입에 대한 심층 분석

class A {
    construct(private b: B) {}
}
class B {}
const a: A = new A(new B());

import { BrowserModule } from '@angular/platform-browser';
import { NgModule, InjectionToken } from '@angular/core';
import { AppComponent } from './components/app/app.component';
import { SingleServiceService } from './service/single-service.service';
import { MyServiceService } from './service/my-service.service';
import { UseServiceService } from './service/use-service.service';
import { ValueServiceService } from './service/value-service.service';
import { ReactiveFormsModule, FormsModule } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http';

export interface AppConfig {
    title: string
}

export const CONFIG = new InjectionToken<AppConfig>(&#39;描述令牌的用途&#39;);

const USE_Config = {
    title: "非类的注入令牌"
}

@NgModule({
    declarations: [
        AppComponent
    ],
    imports: [
        BrowserModule,
        HttpClientModule,
        FormsModule,
        ReactiveFormsModule
    ],
    providers: [
        SingleServiceService,
        // 完整形式
        // {provide: SingleServiceService, useClass: SingleServiceService}
        // provide 属性存有令牌，它作为一个 key，在定位依赖值和配置注入器时使用。
        // 属性二通知如何创建依赖，实际依赖的值可以是useClass、 useExisting、useValue 或 useFactory
        // useExisting起别名,依赖注入也可以注入组件
        {provide: MyServiceService, useClass: UseServiceService},
        // useValue可以是字符串，对象等
        {provide: ValueServiceService, useValue: "依赖注入字符"},
        // 使用 InjectionToken 对象来为非类的依赖选择一个提供者令牌
        { provide: CONFIG, useValue: USE_Config }
    ],
    bootstrap: [AppComponent],
    entryComponents: []
})
export class AppModule { }

import { Injectable } from '@angular/core';

@Injectable()
export class SingleServiceService {

constructor() { }

}

import { Injectable } from '@angular/core';

@Injectable()
export class MyServiceService {

    constructor() { }

    getName(): string {
        return "my-service";
    }
    
}

import { Injectable } from '@angular/core';

@Injectable()
export class UseServiceService {

    constructor() { }

    getName(): string {
        return "use-service";
    }

}

import { Injectable } from '@angular/core';

@Injectable()
export class ValueServiceService {

constructor() { }

}