Error: Uncaught (in promise): NullInjectorError: R3InjectorError(AppModule) Angular 13

Question

The weirdest error I got so far.

I generated a new component in angular 13, and since then I am getting this error. I deleted the component, but I still get the same error. It goes as follows:

The error:

Uncaught (in promise): NullInjectorError: R3InjectorError(AppModule)[HttpService -> ModuleSkillCollectionComponent -> ModuleSkillCollectionComponent -> ModuleSkillCollectionComponent]: NullInjectorError: No provider for ModuleSkillCollectionComponent!

When I scroll down, I come across the following message:

And this takes me to:

<nav class="navbar max-w-full w-full mx-auto">
  <div class="flex-1">
    <div class="w-full top-0 border-b">
      <ul class="menu menu-horizontal w-screen">
        <li class="left-0 top-0 font-bold"><a href="">CompetentieApp</a></li>
        <li class="mr-10">
          <a routerLinkActive="tab-active" href="/faq">Eindniveaus</a>
        </li>
        <li class="mr-10"><a href="/faq">Overzicht Alle Modules</a></li>
        <li class="mr-10"><a href="/faq">Beheer</a></li>
        <li class="mr-10">
          <a routerLinkActive="tab-active" routerLink="moduleCompetenties">Logout</a>
        </li>
        <img
          class="absolute w-14 md:w-36 mr-10 right-0 top-0"
          src="assets/logo.png"
          alt="logo"
        />
      </ul>
    </div>
  </div>
</nav>
<router-outlet></router-outlet>

Here is my app-routing.ts:

const routes: Routes = [
  { path: '', redirectTo: 'home', pathMatch: 'full' },
  { path: 'moduleCompetenties', component: ModuleSkillCollectionComponent },
  { path: '**', redirectTo: 'home', pathMatch: 'full' },
];

@NgModule({
  imports: [
      CommonModule,
      RouterModule.forRoot(routes)
  ],
  exports: [RouterModule],
})
export class AppRoutingModule {}

UPDATE

Here is the http.service.ts :

@Injectable({ providedIn: 'root' })
export class HttpService {


  // moduleSkillJson: ModuleSkillJSON[] = [];
  // private isGetting = false;

  constructor(private http: HttpClient, private moduleSKillClass: ModuleSkillCollectionComponent) {}

  post() {
    this.http.post('http://localhost:8080/add', this.postBody).subscribe(() => {
      console.log(this.postBody);
    });
  }

  getSkill(skillJson: Skill[]) {
    this.http.get<{[key: string] : Skill}>(environment.apiUrl + '/skillCollection')
        .pipe(
            map((res) => {
                  // console.log(res);
                  const skillDetailsArray: Skill[] = [];
                  for (const key in res) {
                    if (res.hasOwnProperty(key)) {
                      skillDetailsArray.push({...res[key], id: key})
                    }
                  }
                  // console.log(skillDetailsArray);
                  return skillDetailsArray;
                }
            )
        ).subscribe(skills => {
          // console.log(skills);
          skillJson = skills;
          // console.log("SkillDetails has " + this.skillJson.length + " entries.");
        }
    );
  }

  getModuleSkill(moduleSkillJson: ModuleSkillJSON[]) {
    this.http
        .get<{[key: string] : ModuleSkillJSON}>(environment.apiUrl + "/moduleSkill")
        .pipe(
            map((res) => {
              // console.log(res);
              const moduleSkill: ModuleSkillJSON[] = [];
              for (const key in res) {
                if (res.hasOwnProperty(key)) {
                  moduleSkill.push({...res[key], id: key})
                }
              }
              console.log(moduleSkill);
              return moduleSkill;
            })
        ).subscribe(moduleSkills => {
      moduleSkillJson = moduleSkills;
      this.moduleSKillClass.entriesLooper(moduleSkillJson);
    });
    // console.log("SkillDetails has " + this.moduleSkillJson.length + " entries.");
  }
}

Here is the App.module.ts :

@NgModule({
  declarations: [AppComponent, ModuleSkillCollectionComponent],
  imports: [
    BrowserModule,
    AppRoutingModule,
    ReactiveFormsModule,
    HttpClientModule,
  ],
  providers: [HttpService],
  bootstrap: [AppComponent],
})
export class AppModule {}

Here is the module-skill-collection.component.ts :

export class ModuleSkillCollectionComponent implements OnInit {
  showTable: Boolean = false;
  loop: boolean = true;
  cohort: string = '22-23';
  moduleSkillJson: ModuleSkillJSON[];
  skillJson: Skill[] = [];
  entries: number[] = [];
  i: number = 1;

    constructor(private service: HttpService) {}

  ngOnInit(): void {
      this.getModuleSkills();
      this.getSkill();
  }

  isActive() {
    this.showTable = !this.showTable;
  }

    counter(i: number) {
        return new Array(i);
    }

    getSkill() {
        this.service.getSkill(this.skillJson);
    }

    getModuleSkills() {
        this.service.getModuleSkill(this.moduleSkillJson);
        this.entriesLooper(this.moduleSkillJson);
    }

    entriesLooper(moduleSKills: ModuleSkillJSON[]): number[] {
        for (let modulesSKill of moduleSKills) {
            this.entries.push(modulesSKill.entry);
        }
        return this.entries;
    }

}

export interface Skill {
    id?: string;
    skillGroupName: string;
    skillGroupType: string;
    skillDetailName: string;
    skillDetailType: string;
}

export interface ModuleSkillJSON {
    moduleCode: string;
    moduleName: string;
    skill: Array<Skill>[];
    entry: number;
    exist: number;
    id?: string;
}

Any idea how to solve it?

Answer 1

I assume HttpService is a wrapper around HttpClient - if so, yay, wrapping things, happy days.

The error suggests that's the issue - that service isn't being provided by anything - either as a big ol' singleton by being provided in the app.module.ts , nor in a sub module nor in the component itself.

Somewhere , there has to be a providers: [HttpService] line.

Outside of that, and I wonder if it's misleading, you're injecting an ElementRef into the component?

How's that working? Typically those are used with @ViewChild() for example, and unless you're creating the components yourself to be able to pass one in, where is the app getting this ElementRef from in order to inject it?

Answer 2

问题是 A 类 (ModuleSkillCollection) 正在 B 类 (HttpService) 的构造函数中初始化，而 B 类正在 A 类的构造函数中初始化。