Learn about android internals(dive deep into the system)

Android Architecture

Layers of Android

Android’s architecture is built in a layered structure, each layer providing specific functionalities and abstracting the lower layers:

• Application Layer: This is where user-installed apps reside, interacting with the system through the framework layer.
• Application Framework Layer: Provides core system services like Activity Manager, Content Providers, and Notification Manager for apps to use.
• Android Runtime (ART): Responsible for executing Dalvik bytecode, which is compiled from Java source code. ART enhances performance through Ahead-of-Time (AOT) compilation.
• Libraries Layer: Contains various libraries for system functionalities, including graphics (OpenGL), multimedia (Media Framework), databases (SQLite), and network protocols.
• Linux Kernel: The bedrock of Android, providing device drivers, memory management, process scheduling, and security features.

Key Components

• Activity Manager: Manages the lifecycle of activities (screens) within apps.
• Content Provider: Allows apps to share data with each other.
• Notification Manager: Handles system-wide notifications displayed to the user.
• Package Manager: Manages the installation, removal, and update of apps.
• Service Manager: Manages system-wide services, such as the power manager and the location service.

Process Management

Zygote Process

The Zygote process is a foundational process in Android, responsible for:

• Preloading common system libraries and resources.
• Forking new processes for each Android app.
• Creating a shared virtual machine (VM) instance for all apps, reducing startup times and memory consumption.

Process States

Android processes can be in different states based on their activity:

Process Priorities

Android prioritizes processes based on their importance and current usage:

• Foreground: Highest priority, essential for the user’s current activity.
• Visible: High priority, important for the user’s overall experience.
• Background: Medium priority, running processes not directly used by the user.
• Empty: Low priority, processes that have minimal resource usage.

Memory Management

Dalvik Heap

The Dalvik heap is a memory space where Android apps allocate their objects. It’s managed by a garbage collector that reclaims unused memory.

Low Memory Killer

The Low Memory Killer is a system service that monitors memory usage and kills processes that are consuming excessive memory when the system is under pressure.

Virtual Memory

Android uses virtual memory to allow processes to access more memory than physically available. The system manages swapping between RAM and storage to optimize memory usage.

Android Binder

Inter-Process Communication (IPC)

Android Binder is a mechanism for inter-process communication, enabling apps and system components to communicate with each other even if they run in different processes.

Client-Server Model

Binder uses a client-server model where a client process can send requests to a server process and receive responses.

Benefits of Binder

• Security: Binder provides a secure way to communicate between processes, ensuring that only authorized processes can access sensitive data.
• Performance: Binder is highly efficient, minimizing overhead and maximizing communication speed.
• Flexibility: Binder supports a wide range of data types and allows for complex communication scenarios.

Android System Services

Services Overview

Android system services are background processes that provide core functionalities to the system and apps. They are managed by the Service Manager.

Key Services

• Activity Manager: Manages the lifecycle of activities and provides window management.
• Power Manager: Controls the system’s power state, including screen brightness and sleep mode.
• Location Manager: Provides location services using GPS, Wi-Fi, and other sensors.
• Notification Manager: Handles system-wide notifications, allowing apps to send alerts to the user.
• WindowManager: Manages the display and its elements, including windows and views.

Example Code: Using the Location Service

package com.example.myapplication;

import android.Manifest;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

public class MainActivity extends AppCompatActivity {

    private TextView locationTextView;
    private LocationManager locationManager;
    private LocationListener locationListener;

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

        locationTextView = findViewById(R.id.locationTextView);

        locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
        locationListener = new LocationListener() {
            @Override
            public void onLocationChanged(Location location) {
                locationTextView.setText("Latitude: " + location.getLatitude() + "\nLongitude: " + location.getLongitude());
            }

            @Override
            public void onStatusChanged(String provider, int status, Bundle extras) {}

            @Override
            public void onProviderEnabled(String provider) {}

            @Override
            public void onProviderDisabled(String provider) {}
        };

        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            // Request permission
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 1);
            return;
        }
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        if (requestCode == 1 && grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
        }
    }
}

// This code snippet demonstrates how to use the Location service, which is one of Android's system services. 
// The code first checks if the app has permission to access the user's location.
// If permission is granted, the app requests location updates from the GPS provider.
// Once the location is updated, the code sets the text view with the latitude and longitude.

Conclusion

Understanding Android internals is crucial for building robust, efficient, and secure apps. This article provided a comprehensive overview of key components, processes, and system services, allowing you to dive deeper into the complexities of the Android operating system.