angularjs 2.0: Can't inject anything through c

Question

I am creating a sample application in angularjs 2.0. While developement I came across with a serious problem - I can't inject anything to the component through the constructor function.

This is the plnkr url : https://plnkr.co/edit/g1UcGmYPLtY8GiXuNHzK?p=preview

I used the following code for importing ItemService from app.item.service.ts

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

Then I specified provider as

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

After that, given code for TodoComponent as

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();
  }
}

When I try to inject ItemService through constructor , I am getting an error : " Error: Can't resolve all parameters for TodoComponent: (?)." I am not able to inject even angularjs providers like Injector.

However, this method works for me :

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

I am using the following versions of libraries for developement as mentioned in my package.json

 "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 version: 2.0.0 final
• Browser: all

attaching the error log I got from console :

(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

You code is fine!

Here is your updated plunker: https://plnkr.co/edit/6SR8Ibljuy0ElEBU87ox?p=preview

Did some changes to your system.js.config!

   // ADDED THESE TWO OPTIONS BELOW

   //use typescript for compilation
   transpiler: 'typescript',
   //typescript compiler options
   typescriptOptions: {
      emitDecoratorMetadata: true
   },

and this..

app: {
   main: './main.ts',     // CHANGES HERE
   defaultExtension: 'ts' // CHANGES HERE
},

Answer 2

I see that your tsconfig.json isn't correct.

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

This is the magic sauce for DI. emitDecoratorMetadata: true. This option will preserve type information in your object's metadata.

See also

• How does the TypeScript Angular DI magic work?
• Injecting services in services in Angular 2