Angular Service单例构造函数多次调用

时间:2018-07-24 15:43:44

标签: angular singleton angular-services angular-router angular-module

我正在尝试使用存储已验证用户详细信息的应用程序范围服务(UserService)。我已经设置了一些路由,但发现每个路由都实例化了UserService。我希望他们共享相同的UserService。

我创建了一个包含TestService作为提供程序的CoreModule,并将其导入到AppModule中。

core.module.ts:

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { TestService } from '../test.service';

@NgModule({
  imports: [
    CommonModule
  ],
  declarations: [],
  providers: [
    TestService
  ]
})
export class CoreModule { }

test.service.ts:

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})
export class TestService {
  constructor() { console.log('testService constructor called');}
}

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { AdminComponent } from './layout/admin/admin.component';
import { AppComponent } from './app.component';
import { AppRoutingModule } from './app-routing.module';


import { CoreModule } from './core/core.module';

@NgModule({
  declarations: [
    AppComponent,
    AdminComponent,
  ],
  imports: [
    BrowserModule,
    AppRoutingModule,
    FormsModule,
    CoreModule
  ],
  providers: [
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

app-routing.module.ts

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { Routes, RouterModule } from '@angular/router';
import { BasicLoginComponent } from './basic-login/basic-login.component';
import { HttpClientModule } from '@angular/common/http';
import { AdminComponent } from './layout/admin/admin.component';    

const routes: Routes = [
  {
    path: '',
    component: AdminComponent,
    children: [
      {
        path: 'home',
        loadChildren: './dashboard/dashboard.module#DashboardModule'
      },
      {
        path: 'user/profile',
        loadChildren: './user-profile/user-profile.module#UserProfileModule'
      }
    ]

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

我已经将TestService注入DashboardComponent和UserProfileComponent构造函数中。但是,当在其中两个组件之间路由时,两次调用TestService构造函数。

这似乎很简单,但是我却无法正确解决。谁能为我指出正确的方向进行故障排除?

*编辑

dashboard.component.ts

import {AfterViewInit, Component, OnInit, ViewEncapsulation} from '@angular/core';
/*import {NotificationsService} from 'angular2-notifications';*/

import { UserService } from '../user.service.js';
import { LocalStorageService } from '../../../node_modules/ngx-webstorage';
import { TestService } from '../test.service.js';

@Component({
  selector: 'app-dashboard',
  templateUrl: './dashboard.component.html',
  styleUrls: ['./dashboard.component.scss'],
  encapsulation: ViewEncapsulation.None
})
export class DashboardComponent implements OnInit, AfterViewInit {


  constructor(private userService:UserService, private localSt:LocalStorageService,
  private testService:TestService) { // private servicePNotify: NotificationsService
  }


  ngOnInit() {

  }

}

user-profile-component.ts:

import {Component, OnInit} from '@angular/core';
import {animate, style, transition, trigger} from '@angular/animations';
import {Http} from '@angular/http';
import { TestService } from '../test.service';

@Component({
  selector: 'app-user-profile',
  templateUrl: './user-profile.component.html',
  styleUrls: [
    './user-profile.component.scss',
    '../../assets/icon/icofont/css/icofont.scss'
  ],

})
export class UserProfileComponent implements OnInit {

  constructor(public http: Http, private userService: UserService,
  private testService:TestService) {
  }

  ngOnInit() {

  }

}

2 个答案:

答案 0 :(得分:10)

您已将TestService声明为-

@Injectable({
  providedIn: 'root'
})

这意味着您要添加到AppRoot模块。

无需在CoreModule中显式添加,因此从CoreModule的提供者中删除。删除以下内容-

providers: [
    TestService
  ]

TestSevice中添加CoreModule中的RootModule时,就是constructor被多次调用的原因。

因此,请使用上方的任意一个。

答案 1 :(得分:0)

@Injectable({ providedIn: 'root' })

  • 带有providedIn选项的root意味着该服务在整个应用程序中都可以作为singleton服务使用。
  • 如果您未添加到任何模块的提供者列表,则不会抱怨类似No provider for xxxservice的{​​{1}} bcz这样的错误。
  • 如果确实添加到列表中,将导致创建新的服务实例,这将给您带来比预期错误的结果。

注意:请确保使用该概念以获得更好的结果。