Caching API responses is a crucial aspect of app development, allowing applications to run more efficiently and provide seamless user experiences. In this guide, we’ll explore how to implement a custom caching mechanism in Ionic using Capacitor, focusing on storing JSON data retrieved from APIs. By the end of this tutorial, you’ll have a firm understanding of caching principles and how to apply them in your Ionic applications.

Understanding the Need for API Caching

Caching API responses can significantly enhance the performance of your application, especially in scenarios where:

• The API responses may take time to retrieve due to network latency.
• Data needs to be frequently accessed, but the underlying API may impose rate limits.
• Users may have intermittent connectivity, requiring the app to operate offline or with cached data.

Using a third-party package for caching may seem convenient, but if the package remains unmaintained, it’s better to implement your own solution. This tutorial walks you through building a simple yet effective caching mechanism leveraging Ionic and Capacitor.

Prerequisites

Before we begin, ensure you have the following prerequisites:

• Basic knowledge of Ionic and Capacitor
• Node.js and npm installed on your system
• An existing Ionic project (or you can create a new blank Ionic application)

Setting Up Your Ionic Project

Start by creating a new blank Ionic application if you don’t already have one:

ionic start MyIonicApp blank
cd MyIonicApp

Installing Required Packages

We need two services to separate API logic and caching logic. First, install the necessary storage dependency:

npm install @ionic/storage-angular

If you want to use SQLite for better performance especially on mobile devices, install the following plugin:

npm install cordova-sqlite-storage

Then, install the required SQLite driver for Ionic Storage:

npm install @ionic/storage-sqlite

Importing Necessary Modules

In your app module, import the necessary modules to set up Ionic Storage:

import { IonicStorageModule } from '@ionic/storage-angular';

@NgModule({
  // ... other imports
  imports: [
    IonicStorageModule.forRoot()
  ],
})
export class AppModule {}

Creating the Caching Service

Next, we will create a caching service that handles the storage and retrieval of cached data. Generate a new service using Ionic CLI:

ionic generate service caching

In the generated service file, import the storage library and implement methods for caching requests:

import { Injectable } from '@angular/core';
import { Storage } from '@ionic/storage-angular';
import { from } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class CachingService {
  constructor(private storage: Storage) {
    this.init();
  }

  private async init() {
    await this.storage.create();
  }

  async cacheRequest(url: string, data: any) {
    const validUntil = Date.now() + 10000; // Cache for 10 seconds
    await this.storage.set(url, { data, validUntil });
  }

  async getCachedRequest(url: string) {
    const cachedData = await this.storage.get(url);
    if (!cachedData) return null;
    if (Date.now() > cachedData.validUntil) {
      await this.storage.remove(url);
      return null;
    }
    return cachedData.data;
  }

  async clearCache() {
    await this.storage.clear();
  }
}

Integrating Caching with API Service

Now that we have our caching service ready, we can integrate it into our API service to manage data retrieval:

1. Generate an API service:

ionic generate service api

2. Inside your API service, import the CachingService and the HttpClient:

import { HttpClient } from '@angular/common/http';
import { CachingService } from './caching.service';

@Injectable({
  providedIn: 'root'
})
export class ApiService {
  constructor(private http: HttpClient, private cachingService: CachingService) {}

  getUsers() {
    const url = 'https://randomuser.me/api/';
    return from(this.cachingService.getCachedRequest(url)).pipe(
      switchMap(cachedData => {
        if (cachedData) {
          return of(cachedData);
        } else {
          return this.http.get(url).pipe(tap(data => this.cachingService.cacheRequest(url, data)));
        }
      })
    );
  }
}

Displaying Cached Data in Your Component

Finally, you can now use your API service in your components to fetch and display user data while benefiting from caching:

import { Component } from '@angular/core';
import { ApiService } from '../services/api.service';

@Component({
  selector: 'app-home',
  templateUrl: 'home.page.html',
  styleUrls: ['home.page.scss'],
})
export class HomePage {
  users: any[] = [];

  constructor(private apiService: ApiService) { }

  ngOnInit() {
    this.loadUsers();
  }

  loadUsers() {
    this.apiService.getUsers().subscribe(data => {
      this.users = data.results;
    });
  }
}

Conclusion

By implementing a caching mechanism, you can significantly improve your app’s performance and user experience. This tutorial covers the essentials of setting up an effective caching layer using Ionic, Capacitor, and SQLite, allowing for smooth offline functionality and reduced API calls.

The code snippets provided in this article can be adapted to fit specific use cases, ensuring your application runs smoothly regardless of network conditions. Happy coding!