Question

我有一个像根目录这样的全局常量，我希望每个组件都可以访问。在另一个stackoverflow问题中，答案是创建一个常量类并将其导入到每个组件。

有没有办法引导常量类，以便应用程序中的每个组件都可以访问它而无需任何其他导入？

到目前为止我有这个但它不起作用，我如何提升常量类然后在我的组件中访问？

constants.ts

export class Constants{
  root_dir: string;

  constructor(){
      this.root_dir = 'http://google.com/'
    }
  }

main.ts

import {bootstrap} from 'angular2/platform/browser'
import {Constants} from './constants'

bootstrap([
  provide(Constants, {useClass: Constants})
]);

random.component.ts

import {Component, bind} from 'angular2/core';
import {Injector} from 'angular2/core';

@Component({
    selector: 'my-app',
    template: `{{test}}`
})

export class RandomComponent{
    test: string;

    constructor(){
        this.test = injector.get(Constants.root_dir);
    }
}

Answer 1

回答你的问题：

使用Constants类的所有组件都需要导入常量文件。
为了使用Constants类，你需要将它注入任何消费组件的构造函数中，从random.component.ts中删除injector.get（）函数，如下所示：

export class App {
  constructor(constants: Constants) {
    this.url = constants.root_dir;
  }
}

您也可以将常量类装饰为@Injectable并将@Inject装入组件的构造函数中。

Here is a working plunker.

在应用程序级别引导共享常量是有益的，这样只能创建一个类的实例并在所有组件之间共享。

Answer 2

import {Component,bind,provide} from 'angular2/core';

import {bootstrap} from 'angular2/platform/browser';
import {FORM_DIRECTIVES} from 'angular2/form';
import {Directive, ElementRef, Renderer, Input,ViewChild,AfterViewInit} from 'angular2/core';
import {Constants} from 'src/constants'
import {ViewChild, Component, Injectable} from 'angular2/core';

@Component({
selector: 'my-app', 
  template: `{{test}}`,
})


export class App {
    test: string;

    constructor(cs:Constants){
        this.test = cs.root_dir;
    }
}

bootstrap(App, [Constants]);

<强> Demo

Answer 3

import {Component} from 'angular2/core'
import { Constants } from './constants'

@Component({
    selector: 'test',
    template: `  
                    Constants: <strong>{{ urlTemplate }}</strong>

              `
    providers:[Constants]

})

export class AppComponent{

  constructor(constants: Constants){
    this.urlTemplate = constants.root_dir;
  }

}

您可以在Constants

中添加providers:[Constants]

装饰者@Injectable在这种情况下没有必要，但谷歌建议总是使用你可以在这里看到：https://angular.io/docs/ts/latest/guide/dependency-injection.html#!#why-injectable-

/*
We recommend adding @Injectable() to every service class, even those that don't have dependencies and, therefore, do not technically require it. Here's why:
Future proofing: No need to remember @Injectable when we add a dependency later.
Consistency: All services follow the same rules, and we don't have to wonder why a decorator is missing
*/

//@Injectable() 
export class Constants{
  root_dir: string;

  constructor(){
      this.root_dir = 'http://google.com/'
    }
  }

`Plunker`

关于@Inject使用，你可以在这里阅读： what is the difference between using (@Inject(Http) http: Http) or not

现在，如果您想要全局，可以添加bootstrap

//main entry point
import {bootstrap} from 'angular2/platform/browser';
import {AppComponent} from './app';
import { Constants } from './constants';


bootstrap(AppComponent, Constants)
  .catch(err => console.error(err));

//import { Injectable } from 'angular2/core'

//@Injectable()
export class Constants{
root_dir: string;

  constructor(){
      this.root_dir = 'http://google.com/'
    }
  }

import {Component, Inject} from 'angular2/core'
import { Constants } from './constants';

@Component({
    selector: 'test',
    template: `  
                    Constants: <strong>{{ urlTemplate }}</strong>

              `

})


export class AppComponent{

  constructor(@Inject (Constants) constants: Constants){
    this.urlTemplate = constants.root_dir;
  }

}

Angular 2全局常量提供者注入方法

3 个答案:

`Plunker`

`Plunker`