意外的值'HttpClient'

Question

这是我的app.module.ts文件

import { BrowserModule } from '@angular/platform-browser';
import { ErrorHandler, NgModule } from '@angular/core';
import { IonicApp, IonicErrorHandler, IonicModule } from 'ionic-angular';
import { SplashScreen } from '@ionic-native/splash-screen';
import { StatusBar } from '@ionic-native/status-bar';
import { HttpClient } from '@angular/common/http';

import { MyApp } from './app.component';
import { HomePage } from '../pages/home/home';
import { DataProvider } from '../providers/data/data';

@NgModule({
  declarations: [
    MyApp,
    HomePage,
  ],
  imports: [
    BrowserModule,
    HttpClient,
    IonicModule.forRoot(MyApp)
  ],
  bootstrap: [IonicApp],
  entryComponents: [
    MyApp,
    HomePage
  ],
  providers: [
    StatusBar,
    SplashScreen,
    {provide: ErrorHandler, useClass: IonicErrorHandler},
    DataProvider
  ]
})
export class AppModule {}

我收到这样的错误:

Uncaught Error: Unexpected value 'HttpClient' imported by the module
'AppModule'. Please add a @NgModule annotation.
    at syntaxError (compiler.js:486)
    at compiler.js:15240
    at Array.forEach (<anonymous>)
    at CompileMetadataResolver.getNgModuleMetadata (compiler.js:15215)
    at JitCompiler._loadModules (compiler.js:34413)
    at JitCompiler._compileModuleAndComponents (compiler.js:34374)
    at JitCompiler.compileModuleAsync (compiler.js:34268)
    at CompilerImpl.compileModuleAsync (platform-browser-dynamic.js:239)
    at PlatformRef.bootstrapModule (core.js:5578)
    at Object.199 (main.ts:5) syntaxError @ compiler.js:486 (anonymous) @ compiler.js:15240
CompileMetadataResolver.getNgModuleMetadata @ compiler.js:15215
JitCompiler._loadModules @ compiler.js:34413
JitCompiler._compileModuleAndComponents @ compiler.js:34374
JitCompiler.compileModuleAsync @ compiler.js:34268
CompilerImpl.compileModuleAsync @ platform-browser-dynamic.js:239
PlatformRef.bootstrapModule @ core.js:5578 199 @ main.ts:5
__webpack_require__ @ bootstrap c2d88ebb0bb27539f897:54 webpackJsonpCallback @ bootstrap c2d88ebb0bb27539f897:25 (anonymous) @
main.js:1

Answer 1

你必须在导入import模块HttpClientModule和引用.

// reference the module
import { HttpClientModule } from '@angular/common/http';

  imports: [
    BrowserModule,
    HttpClientModule, // import the module
    IonicModule.forRoot(MyApp)
  ]

Answer 2

您正在使用HttpClient模块而不是HttpClientModule. 因此，将两个导入中的HttpClientwith替换HttpCLientModule为

import { HttpClientModule } from '@angular/common/http';

和

  imports: [
    BrowserModule,
    HttpClientModule, 
    IonicModule.forRoot(MyApp)
  ]

Answer 3

Angular 4.3 引入了一个新模块 ，HttpClientModule它是对现有HttpModule.

import { HttpModule } from '@angular/http';

to:

import { HttpClientModule } from '@angular/common/http';

第二步是用新服务替换服务 Http 的每个实例HttpClient。

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

@Injectable()
export class UserService {

  constructor(private http: HttpClient) {}

  list(): Observable<UserModel> {
    return this.http.get('/api/users');
  }
}