Where to save settings like API url in Ionic2 app?

This question already has an answer here:

Ionic2/Angular2 - Read a custom config file 2 answers

I have several settings which should be in a configuration file.

For example: URL of APIs

Where is the best place for it in Ionic 2?

回答1:

From Angular 2/4 Docs:

Non-class dependencies

What if the dependency value isn't a class? Sometimes the thing we want to inject is a string, function, or object.

Applications often define configuration objects with lots of small facts (like the title of the application or the address of a web API endpoint) but these configuration objects aren't always instances of a class.

One solution to choosing a provider token for non-class dependencies is to define and use an OpaqueToken

So you would need to define a config object with the urls and so on, and then an OpaqueToken to be able to use it when injecting the object with your configuration.

I included all my configuration in the app-config.ts file

// Although the ApplicationConfig interface plays no role in dependency injection, 
// it supports typing of the configuration object within the class.
export interface ApplicationConfig {
  appName: string;
  apiEndpoint: string;
}

// Configuration values for our app
export const MY_CONFIG: ApplicationConfig = {
  appName: 'My new App',
  apiEndpoint: 'http://www...'
};

// Create a config token to avoid naming conflicts
export const MY_CONFIG_TOKEN = new OpaqueToken('config');

What OpaqueToken is may be confusing at first, but it just a string that will avoid naming conflicts when injecting this object. You can find an amazing post about this here.

Then, you just need to include it in the page you need it like this:

import { NavController } from 'ionic-angular/index';
import { Component, OpaqueToken, Injectable, Inject } from "@angular/core";

// Import the config-related things
import { MY_CONFIG_TOKEN, MY_CONFIG, ApplicationConfig } from 'app-config.ts';

@Component({
  templateUrl:"home.html",
  providers: [{ provide: MY_CONFIG_TOKEN, useValue: MY_CONFIG }]
})
export class HomePage {

  private appName: string;
  private endPoint: string;

  constructor(@Inject(MY_CONFIG_TOKEN) private config: ApplicationConfig) {
    this.appName = config.appName;
    this.endPoint = config.apiEndpoint;
  }
}

Please notice how to include it in the providers array

providers: [{ provide: MY_CONFIG_TOKEN, useValue: MY_CONFIG }]

And how to tell the injector how it should obtain the instance of the config object

@Inject(MY_CONFIG_TOKEN) private config: ApplicationConfig

UPDATE

OpaqueToken has been deprecated since v4.0.0 because it does not support type information, use InjectionToken<?> instead.

So instead of these lines:

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

// Create a config token to avoid naming conflicts
export const MY_CONFIG_TOKEN = new OpaqueToken('config');

Now we should use

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

// Create a config token to avoid naming conflicts
export const MY_CONFIG_TOKEN = new InjectionToken<ApplicationConfig>('config');

回答2:

Save them in a class singleton ( generally an anti-pattern) or even better Namespace equivalent.

class Singleton {
    /* ... lots of singleton logic ... */
    public someMethod() { ... }
}

// Using
var x = Singleton.getInstance();
x.someMethod();

Namespace equivalent

namespace Singleton {
    export function someMethod() { ... }
}
// Usage
Singleton.someMethod();
var x = Singleton; // If you need to alias it for some reason

回答3:

You may use either WebSQL or SQLite table or LocalStorage since both methods are very well supported by Ionic and hybrid Apps frameworks.