当 Ionic 2 中的值发生变化时检索本地存储值

Retrieve localstorage value when value is change in Ionic 2(当 Ionic 2 中的值发生变化时检索本地存储值)

问题描述

我正在使用 ionic 2 框架，并尝试使用本地存储来存储网络状态

I am using ionic 2 framework and I have tried using local storage to store a network status

this.local = new Storage(LocalStorage);
this.local.set("status", this.status);

有两个值可以动态分配给状态，强"和弱".

There are 2 values that, "Strong" and "Weak" that can be assigned to status dynamically.

我能够在每个页面初始化时获取我的本地存储状态"值的初始值.

I am able to get my the initial value of my local storage "status" value on initialization of every page.

toCheckStatus();
function toCheckStatus()
{
    self.local = new Storage(LocalStorage);
    self.local.get('status').then((value) => 
    {
        console.log("status", value);
    });
}

这将返回一个强"或弱"，这正是我想要的，但是否有任何方法或事件可以动态(在状态"值更改时)调用toCheckStatus()"函数?

this will return me a "Strong" or "Weak", which is what I want, but is there any methods or event to dynamically (On "status" value change) call "toCheckStatus()" function?

工作流程示例(伪代码):

Workflow Example (pseudo-code):

1. 在应用程序启动时 -> 检查互联网状态(后台将不断检查并更新本地存储值)
2. 将状态存储到本地存储
3. 调用函数获取值(我的值变化时如何动态调用这个函数，有什么方法吗?)
4. 如果状态为弱 -> 显示弱图标
5. 如果状态为强 -> 显示强图标

推荐答案

我的值变化时如何动态调用这个函数，有什么方法吗?

How to dynamically call this function when my value change, is there any method?

更好的解决方案是使用 observables.您可以在方法中使用 observables 在属性更改时发出事件，然后执行您需要执行的代码.

A better solution will be using observables. You can use observables in your methods to emit events when a property is changed and then execute the code you need to execute.

这是一个非常简单的使用observables的例子:

This is a very simple example of using observables:

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

@Injectable()
export class StorageService {

    private storageObserver: any;
    public storage: any;

    constructor(...) {
        this.storageObserver= null;

        this.storage= Observable.create(observer => {
            this.storageObserver= observer;
        });
    }

    public yourMethod(): void { 

        // This method changes the value of the storage
        // ...

        // Notify to the subscriptor that the value has changed
        this.storageObserver.next(newValue);
    }

然后在你的页面中:

@Component({
  templateUrl: 'build/pages/my-new-page/my-new-page.html',
  providers: [..., StorageService ]
})
export class MyNewPage {

    constructor(..., private storageService : StorageService ) {

        // Initialize all the things you need
        // ... 

        this.storageService.storage.subscribe((newValue) => {
                // This code will execute when the property has changed and also
                // you'll have access to the object with the information that
                // your service sent in the next() call.
                this.doWhatYouWant(newValue);
        });
    }
}

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如果您需要更新视图中的某些内容，因为后台发生了更改，您必须让 Angular 知道该更改.一种方法是使用 Zones.您可以查看我的答案这里 知道该怎么做.

If you need to update something in the view, beacuse of something that has changed in the background, you will have to let Angular know of that change. One way to do it is by using Zones. You can check my answer here to know how to do it.

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