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[英]How to fix ERROR Error: Uncaught (in promise): NullInjectorError: StaticInjectorError(AppModule)[HomeComponent -> HttpHeaders]
[英]Getting error as "NullInjectorError: StaticInjectorError(AppModule)[ContactService -> HttpHeaders]"
我嘗試了所有可能的解決方案,例如在 app.module.ts 中導入 HttpClientModule 以及搜索此錯誤消息時給出的所有建議,但沒有解決我的問題。 我是否錯過了 .ts 文件中的任何設置。
//contact.service.ts
import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { HttpClientModule } from '@angular/common/http';
import { Contact } from './contact';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';
@Injectable({
providedIn: 'root'
})
export class ContactService {
constructor(private http:HttpClient, headers:HttpHeaders) { }
//retrewing contacts
getContacts(){
return this.http.get('http://localhost:3000/api/contacts')
.pipe(map(res => res));
}
// Adding contacts
addContacts(newContact){
var headers = new HttpHeaders();
headers.append('Content-Type','application/json');
return this.http.post('http://localhost:3000/api/add',newContact, {headers:headers})
.pipe(map(res => res));
}
//delete contacts
deleteContacts(id){
return this.http.delete('http://localhost:3000/api/delete'+id)
.pipe(map(res => res));
}
}
我的contacts.component.ts
import { Component, OnInit } from '@angular/core';
import { ContactService } from '../contact.service';
import { Contact } from '../contact';
import { HttpClientModule } from '@angular/common/http';
@Component({
selector: 'app-contacts',
templateUrl: './contacts.component.html',
styleUrls: ['./contacts.component.css'],
providers: [ContactService]
})
export class ContactsComponent implements OnInit {
contacts : any;
contact : Contact;
first_name : string;
last_name : string;
phone_no : string;
constructor(private contactService:ContactService) { }
ngOnInit() {
this.contactService.getContacts()
.subscribe(contacts=>
this.contacts = contacts);
}
}
我的 app.module.ts
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';
import { ContactsComponent } from './contacts/contacts.component';
import { HttpClientModule } from '@angular/common/http';
import { HttpClient } from '@angular/common/http';
@NgModule({
declarations: [
AppComponent,
ContactsComponent
],
imports: [
BrowserModule,
AppRoutingModule,
HttpClientModule
],
providers: [HttpClientModule],
bootstrap: [AppComponent]
})
export class AppModule { }
我已在上述所有內容中添加了 httpclientmodule,但仍然收到錯誤消息,我是否需要添加更多設置。
沒有HttpHeaders
提供者。 您不注入HttpHeaders
實例,您只需根據需要創建實例,您已經在這樣做了。
您可以通過從ContactService
構造函數中刪除注入的HttpHeaders
來解決此問題。
export class ContactService {
constructor(private http:HttpClient) { }
}
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