Javascript 实例化 Injectable 类时未调用 ngOnInit
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StackOverFlow
ngOnInit not being called when Injectable class is Instantiated
提问by Levi Fuller
Why isn't ngOnInit()called when an Injectableclass is resolved?
为什么ngOnInit()在Injectable解决类时不调用？
Code
代码
import {Injectable, OnInit} from 'angular2/core';
import { RestApiService, RestRequest } from './rest-api.service';
@Injectable()
export class MovieDbService implements OnInit {
constructor(private _movieDbRest: RestApiService){
window.console.log('FROM constructor()');
}
ngOnInit() {
window.console.log('FROM ngOnInit()');
}
}
Console Output
控制台输出
FROM constructor()
回答by Sasxa
Lifecycle hooks, like OnInit()work with Directives and Components. They do not work with other types, like a service in your case. From docs:
生命周期钩子，就像OnInit()使用指令和组件一样。它们不适用于其他类型，例如您的服务。从文档：
A Component has a lifecycle managed by Angular itself. Angular creates it, renders it, creates and renders its children, checks it when its data-bound properties change and destroy it before removing it from the DOM.
Directive and component instances have a lifecycle as Angular creates, updates, and destroys them.
组件具有由 Angular 本身管理的生命周期。Angular 创建它，渲染它，创建并渲染它的子元素，在它的数据绑定属性改变时检查它，并在将它从 DOM 中删除之前销毁它。
指令和组件实例在 Angular 创建、更新和销毁它们时具有生命周期。
回答by SBD580
I don't know about all the lifecycle hooks, but as for destruction, ngOnDestroyactually get called on Injectable when it's provider is destroyed (for example an Injectable supplied by a component).
我不知道所有的生命周期钩子，但至于销毁，ngOnDestroy当它的提供者被销毁时，实际上会在 Injectable 上被调用（例如一个由组件提供的 Injectable）。
From the docs :
来自 docs :
Lifecycle hook that is called when a directive, pipe or serviceis destroyed.
当指令、管道或服务被销毁时调用的生命周期钩子。
Just in case anyone is interested in destructioncheck thisquestion:
以防万一有人对破坏感兴趣，请检查这个问题：
回答by AJ Richardson
Note: this answer applies only to Angular components and directives, NOT services.
注意：此答案仅适用于 Angular 组件和指令，不适用于服务。
I had this same issue when ngOnInit(and other lifecycle hooks) were not firing for my components, and most searches led me here.
当ngOnInit（和其他生命周期钩子）没有为我的组件触发时，我遇到了同样的问题，并且大多数搜索将我带到这里。
The issue is that I was using the arrow function syntax (=>) like this:
问题是我使用了这样的箭头函数语法 ( =>)：
class MyComponent implements OnInit {
// Bad: do not use arrow function
public ngOnInit = () => {
console.log("ngOnInit");
}
}
Apparently that does not work in Angular 6. Using non-arrow function syntax fixes the issue:
显然这在 Angular 6 中不起作用。使用非箭头函数语法解决了这个问题：
class MyComponent implements OnInit {
public ngOnInit() {
console.log("ngOnInit");
}
}
回答by Eduardo A EDUARDO Fernandez Di
I had to call a function once my dataService was initialized, instead, I called it inside the constructor, that worked for me.
一旦我的 dataService 被初始化，我就必须调用一个函数，相反，我在构造函数中调用了它，这对我有用。
回答by HSN KH
import {Injectable, OnInit} from 'angular2/core';
import { RestApiService, RestRequest } from './rest-api.service';
import {Service} from "path/to/service/";
@Injectable()
export class MovieDbService implements OnInit {
userId:number=null;
constructor(private _movieDbRest: RestApiService,
private instanceMyService : Service ){
// do evreything like OnInit just on services
this._movieDbRest.callAnyMethod();
this.userId = this.instanceMyService.getUserId()
}
