Ionic 3、Angular 4 中的单例 [英] Singletons in Ionic 3, Angular 4

问题描述

我将服务定义为类，如下所示:

I am defining service as class, something like this:

@Injectable()
export class MyService {
 ...
}

在其他组件或页面中，我只使用 import 命令导入该类.

In other components or pages, I am importing that class with just import command.

import { MyService } from '../pages/services/myservice';

在构造函数中:

constructor(public _MyService: MyService)

在我的主 app.module.ts 中，我将该类服务添加为提供者.

In my main app.module.ts I have added that class service as provider.

providers: [someOtherThings, MyService, someOtherThings]

在 Ionic 2 中，一切正常.服务是单例的.

In Ionic 2, things are working as expected. Service is singleton.

但在使用 angular 4 的 Ionic 3 中，看起来每个组件都在创建该类的新实例.

But in Ionic 3, which uses angular 4, it looks like every component is creating new instance of that class.

是否有一些新方法可以在 Angular 4 中创建单例服务类?

Is there some new way of creating singleton services classes in angular 4?

推荐答案

我使用 ionic 3 和延迟加载 Angular 4 并且没有问题.要使其成为单例，请确保您的应用程序模块提供服务.并删除 @Component 上使用该服务的提供程序.

Im using ionic 3 with lazyload an angular 4 and not having the issues. To make it singleton make sure your app module provide the service. and remove providers on @Component that use the service.

应用模块

@NgModule({
  ...

  providers: [
    StatusBar,
    SplashScreen,
    { provide: ErrorHandler, useClass: IonicErrorHandler },
    Singleton // the service or provider to be single ton
  ]
})
export class AppModule { }

服务

import { Injectable } from '@angular/core';
import 'rxjs/add/operator/map';

@Injectable()
export class Singleton {

  data = "init data";
  constructor() {
    console.log('Hello Singleton Provider');
  }

  set(data){
    this.data = data;
  }

  log(){
    console.log(this.data);   
  }
}

在离子页面上的服务案例

首页

import { Component } from '@angular/core';
import { IonicPage, NavController, NavParams } from 'ionic-angular';
import { Singleton } from '../../providers/singleton';

@IonicPage()
@Component({
  selector: 'page-first',
  templateUrl: 'first.html'
})
export class FirstPage {
  constructor(public navCtrl: NavController, public navParams: 
  NavParams,private single:Singleton) {
  }

  ionViewDidLoad() {
    console.log('ionViewDidLoad First');
    this.single.log(); // log init data;
    this.single.set("First singleton data");
  }

}

第二页

import { Component } from '@angular/core';
import { IonicPage, NavController, NavParams } from 'ionic-angular';
import { Singleton } from '../../providers/singleton';

@IonicPage()
@Component({
  selector: 'page-second',
  templateUrl: 'second.html'
})
export class SecondPage {
  constructor(public navCtrl: NavController, public navParams: 
  NavParams,private single:Singleton) {
  }

  ionViewDidLoad() {
    console.log('ionViewDidLoad Second');
    this.single.log(); // log First singleton data
  }

}

第三页如果在组件上添加提供程序，它会创建新实例

Third Page it create new instance if providers added on component

import { Component } from '@angular/core';
import { IonicPage, NavController, NavParams } from 'ionic-angular';
import { Singleton } from '../../providers/singleton';

@IonicPage()
@Component({
  selector: 'page-second',
  templateUrl: 'second.html',
  providers:[Singleton] // wrong because its create a new instance
})
export class ThirdPage {
  constructor(public navCtrl: NavController, public navParams: 
  NavParams,private single:Singleton) {
  }

  ionViewDidLoad() {
    console.log('ionViewDidLoad ThirdPage');
    this.single.log(); // log init data
  }

}

确保删除组件上的提供程序以使其成为单例.

make sure to remove the providers on component to make it singleton.

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