K M Rejowan Ahmmed/Android Activity Lifecycle: A Comprehensive Guide

Introduction

When developing Android applications, understanding the lifecycle of an activity is crucial. The activity lifecycle refers to the series of states an activity goes through, from creation to destruction. By understanding this lifecycle, developers can effectively manage resources, handle user interactions, and ensure a seamless user experience. In this blog post, we will dive deep into the Android activity lifecycle, exploring each state and its significance.

What is Activity Lifecycle?

The activity lifecycle consists of various states that an activity transitions through during its lifespan. These states include:

1. onCreate(): This method is called when the activity is first created. It is typically used to initialize essential components, such as UI elements and variables.

2. onStart(): After onCreate(), the activity enters the started state. Here, the activity becomes visible to the user, but it may not be in the foreground.

3. onResume(): The resumed state indicates that the activity is now in the foreground and ready to interact with the user. This is where animations, music playback, and other foreground operations are typically started.

4. onPause(): When an activity loses focus but remains visible, it enters the paused state. This can happen when another activity is launched in front of it or when the device enters a multi-window mode.

5. onStop(): The stopped state occurs when the activity is no longer visible to the user. This can happen when the user navigates to another activity or when the activity is destroyed.

6. onRestart(): If an activity was stopped and then restarted, the onRestart() method is called before onStart(). It allows the activity to prepare for being visible to the user again.

7. onDestroy(): The destroyed state indicates that the activity is about to be destroyed and removed from memory. This is the final opportunity to release any resources or perform cleanup operations.

Lifecycle with Example Codes

Now let’s explore each lifecycle method in detail, accompanied by example code snippets and corresponding log outputs.

onCreate()

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.d("Lifecycle", "onCreate() called");
}

Log Output:

Lifecycle: onCreate() called

onStart()

@Override
protected void onStart() {
    super.onStart();
    Log.d("Lifecycle", "onStart() called");
}

Log Output:

Lifecycle: onStart() called

onResume()

@Override
protected void onResume() {
    super.onResume();
    Log.d("Lifecycle", "onResume() called");
}

Log Output:

Lifecycle: onResume() called

onPause()

@Override
protected void onPause() {
    super.onPause();
    Log.d("Lifecycle", "onPause() called");
}

Log Output:

Lifecycle: onPause() called

onStop()

@Override
protected void onStop() {
    super.onStop();
    Log.d("Lifecycle", "onStop() called");
}

Log Output:

Lifecycle: onStop() called

onRestart()

@Override
protected void onRestart() {
    super.onRestart();
    Log.d("Lifecycle", "onRestart() called");
}

Log Output:

Lifecycle: onRestart() called

onDestroy()

@Override
protected void onDestroy() {
    super.onDestroy();
    Log.d("Lifecycle", "onDestroy() called");
}

Log Output:

Lifecycle: onDestroy() called

Full Code of an Activity with All Lifecycle Methods

Here’s an example of a complete activity class that demonstrates all the lifecycle methods:

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d(TAG, "onCreate() called");
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.d(TAG, "onStart() called");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "onResume() called");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.d(TAG, "onPause() called");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.d(TAG, "onStop() called");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.d(TAG, "onRestart() called");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy() called");
    }
}

Comparison Table of Activity Lifecycle Methods

Importance of Using Activity Lifecycle

1. Resource Management: By properly handling lifecycle methods, you can efficiently manage resources like memory, CPU, and network connections.

2. State Preservation: Lifecycle methods allow you to save and restore the state of your activity.

3. User Experience: Managing the activity lifecycle ensures a smooth user experience.

Best Practices for Using Activity Lifecycle

1. Avoid Lengthy Operations: Perform heavy operations, such as network requests, in background threads.

2. Save and Restore State: Preserve important data during configuration changes.

3. Release Resources: Unregister receivers, release references to objects, and clean up resources.

4. Test Different Scenarios: Test your app under various scenarios.

Refer to the official Android Activity Lifecycle documentation for more information.