导入的服务始终为空

Question

我的组件中导入了以下服务，但不知何故它始终为空。

这是我的应用模块：

import { HttpClientModule } from '@angular/common/http';
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';

import { TodayComponent } from './components/today/today.component';
import { WeekComponent } from './components/week/week.component';


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

我的服务

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { HttpClient } from '@angular/common/http';

@Injectable({
  providedIn: 'root'
})

export class TodayService {

  constructor(private http: HttpClient) { }

  public today(object?): Observable<any> {
    return this.http.get(`https://api.openweathermap.org/data/2.5/weather`, { params: object });
  }

}

我使用它的组件：

import { TodayService } from '../../services/today.service';

  constructor(
    public todayService: TodayService,
    @Inject(DOCUMENT) private document: Document) {
  }

  public SUB_today: Subscription;
  public success(pos: any) {
    var crd = pos.coords;
    this.SUB_today = this.todayService.today({lat: crd.latitude, lon: crd.longitude, appid: '**************'}).subscribe((res)=>{
      this.today = res;
      this.playingWithBG();
    })
  }

一切似乎都是正确的，我在编译器中没有收到任何错误，但是每当我运行我得到的代码：

ERROR TypeError: Cannot read properties of null (reading 'todayService')

直接链接错误与以下代码部分：this.SUB_today = this.todayService.today

Answer 1

尝试在构造函数中注入一个 todaySErvice 的对象，实际上它是空的，因为你不使用它。

Answer 2

错误实际上说 this 是 null。所以在这里：this.todayService，您正在尝试阅读 null.todayService。

this 怎么可能是 null？由于您调用函数 success 的方式（如问题评论中所述）

navigator.geolocation.getCurrentPosition(this.success, this.error);

您可以显式绑定 this :

navigator.geolocation.getCurrentPosition(this.success.bind(this), this.error.bind(this));

或提供一个 lambda :

navigator.geolocation.getCurrentPosition(() => this.success(), () => this.error());

导入的服务始终为空

Imported service is always null

service

constructor

angular