angularjs 2.0：无法通过组件Constructor（）注入任何东西

Question

我正在angularjs 2.0中创建一个示例应用程序。在开发过程中，我遇到了一个严重的问题-我无法通过构造函数向组件注入任何东西。

这是plnkr网址：https
://plnkr.co/edit/g1UcGmYPLtY8GiXuNHzK
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preview

我使用以下代码从app.item.service.ts导入ItemService

import { ItemService } from './app.item.service';

然后我指定提供者为

@Component({
  selector: 'list-todo',
  template: `
    <ul>
    <li *ngFor="let item of items">{{item.text}}</li>
    </ul> 
  `,
  providers : [ItemService]
})

之后，给定TodoComponent的代码为

export class TodoComponent implements OnInit {
  items:Array<Object> = [];
  constructor(private itemService: ItemService){  //here is the problem
   }

  ngOnInit(){
    this.getItems();
  }
  getItems(){
    this.items = this.itemService.getItems();
  }
}

当我尝试通过构造函数注入ItemService时，出现错误：“错误：无法解析TodoComponent的所有参数：（？）。”
我什至无法注入Injector之类的angularjs提供程序。

但是，此方法对我有用：

const injector =  ReflectiveInjector.resolveAndCreate([ItemService]);
this.itemService = injector.get(ItemService);

我正在使用package.json中提到的以下版本的库进行开发

 "dependencies": {
    "@angular/common": "2.0.0",
    "@angular/compiler": "2.0.0",
    "@angular/core": "2.0.0",
    "@angular/forms": "2.0.0",
    "@angular/http": "2.0.0",
    "@angular/platform-browser": "2.0.0",
    "@angular/platform-browser-dynamic": "2.0.0",
    "@angular/router": "3.0.0",
    "@angular/upgrade": "2.0.0",
    "core-js": "^2.4.1",
    "reflect-metadata": "^0.1.3",
    "rxjs": "5.0.0-beta.12",
    "systemjs": "0.19.27",
    "zone.js": "^0.6.23",
    "angular2-in-memory-web-api": "0.0.20",
    "bootstrap": "^3.3.6"
  },
  "devDependencies": {
    "concurrently": "^2.2.0",
    "lite-server": "^2.2.2",
    "typescript": "^2.0.2",
    "typings":"^1.3.2"
  }

• Angular版本：2.0.0最终版
• 浏览器：全部

附加我从控制台获得的错误日志：

(index):16 Error: Error: Can't resolve all parameters for TodoComponent: (?).
        at CompileMetadataResolver.getDependenciesMetadata (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:14404:21)
        at CompileMetadataResolver.getTypeMetadata (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:14301:28)
        at CompileMetadataResolver.getDirectiveMetadata (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:14074:30)
        at eval (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:14167:51)
        at Array.forEach (native)
        at CompileMetadataResolver.getNgModuleMetadata (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:14161:51)
        at RuntimeCompiler._compileComponents (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:16803:49)
        at RuntimeCompiler._compileModuleAndComponents (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:16741:39)
        at RuntimeCompiler.compileModuleAsync (http://localhost:3000/node_modules/@angular/compiler/bundles/compiler.umd.js:16732:23)
        at PlatformRef_._bootstrapModuleWithZone (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:6954:29)
    Evaluating http://localhost:3000/dist/main.js
    Error loading http://localhost:3000/dist/main.js(anonymous function) @ (index):16ZoneDelegate.invoke @ zone.js:203Zone.run @ zone.js:96(anonymous function) @ zone.js:462ZoneDelegate.invokeTask @ zone.js:236Zone.runTask @ zone.js:136drainMicroTaskQueue @ zone.js:368ZoneTask.invoke @ zone.js:308

Answer 1

我发现您的tsconfig.json不正确。

{ 
  "compilerOptions": { 
    "target": "es5", 
    "module": "commonjs", 
    "moduleResolution": "node", 
    "sourceMap": false, 
    "emitDecoratorMetadata": true, <== it should be true 
    "experimentalDecorators": true, 
    "removeComments": false, 
    "noImplicitAny": false, 
    "outDir": "dist" 
  } 
}

这是DI的神奇调味料。 glowDecoratorMetadata：true 。此选项会将类型信息保留在对象的元数据中。

也可以看看

• TypeScript Angular DI魔术如何工作？
• 在服务中注入服务在Angular 2