How to communicate App with Server without internet connection?

Communicating Apps with Servers Offline

In the realm of mobile application development, it’s often desirable for apps to function seamlessly, even when an internet connection is unavailable. This article explores various techniques for enabling communication between apps and servers without relying on an active internet connection.

Offline Data Storage

Local Databases

Local databases provide a robust solution for storing app data offline. Popular choices include:

• SQLite: An embedded database commonly used in Android and iOS apps.
• Realm: An object-oriented database offering fast performance and ease of use.

File Storage

Simple file storage mechanisms can be utilized for storing data offline. Options include:

• Plain Text Files: Suitable for storing small amounts of data in a human-readable format.
• JSON Files: A popular choice for storing structured data in a human-readable format.
• Binary Files: Efficient for storing large amounts of data in a compact format.

Synchronization Strategies

Background Synchronization

Once an internet connection becomes available, the app can synchronize the local data with the server. This process typically involves:

• Uploading Changes: Sending data from the local database to the server.
• Downloading Updates: Fetching updated data from the server and merging it with the local database.

Push Notifications

Push notifications can be used to inform users about updates or changes that need to be synchronized with the server.

Code Example (Android – SQLite)

Database Class

package com.example.offlineApp;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class OfflineDatabaseHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "offline_data.db";
    private static final int DATABASE_VERSION = 1;

    public OfflineDatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // Create tables and define their structure
        db.execSQL("CREATE TABLE items (id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, description TEXT)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Handle database upgrades
    }
}

Data Storage Class

package com.example.offlineApp;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class DataStorage {

    private OfflineDatabaseHelper dbHelper;

    public DataStorage(Context context) {
        dbHelper = new OfflineDatabaseHelper(context);
    }

    public void saveItem(String name, String description) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("name", name);
        values.put("description", description);
        db.insert("items", null, values);
        db.close();
    }

    public Cursor getAllItems() {
        SQLiteDatabase db = dbHelper.getReadableDatabase();
        return db.query("items", null, null, null, null, null, null);
    }
}

Data Retrieval in Activity

package com.example.offlineApp;

import android.database.Cursor;
import android.os.Bundle;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        DataStorage storage = new DataStorage(this);
        Cursor cursor = storage.getAllItems();
        TextView textView = findViewById(R.id.dataTextView);

        if (cursor.moveToFirst()) {
            StringBuilder data = new StringBuilder();
            do {
                data.append("Name: ").append(cursor.getString(1)).append("\n");
                data.append("Description: ").append(cursor.getString(2)).append("\n\n");
            } while (cursor.moveToNext());
            textView.setText(data.toString());
        } else {
            textView.setText("No data available");
        }
    }
}

Comparison Table

Conclusion

Developing apps that function seamlessly even in the absence of an internet connection requires careful consideration of data storage and synchronization techniques. By leveraging local databases, file storage, and appropriate synchronization strategies, developers can empower their apps to provide a consistent and reliable user experience, regardless of network connectivity.