Creatnig an Activity in Android

1. Extend the Activity class or its subclasses
2. Declare the Activity in AndroidManifest.xml
3. Create a layout and set it in Activity's onCreate method

Example manifest declaration:

<activity
    android:name=".TestActivity"
    android:exported="true"
    android:theme="@style/Theme.AppCompat.Light.NoActionBar"
    android:screenOrientation="portrait">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

Activity Lifecycle Methods

Key lifecycle callbacks:

Starting:
onCreate -> onStart -> onResume

Background:
onPause -> onStop

Returning:
onRestart -> onStart -> onResume

Exiting:
onPause -> onStop -> onDestroy

Activity Launch Modes

Four launch modes defined in manifest:

1. standard (default) - Creates new instance each time
2. singleTop - Reuses if already at top of stack
3. singleTask - Reuses if exists in stack, clears above
4. singleInstance - Global singleton in separtae stack

Example singleTop implementation:

<activity
    android:name=".MainActivity"
    android:launchMode="singleTop"
    android:exported="true">
</activity>

Fragment Fundamentals

Key characteristics:

• Has independent lifecycle
• Depends on host Activity
• Can be retrieved via FragmentManager

Basic fragment creation:

public class SampleFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_sample, container, false);
    }
}

Fragment Communication Patterns

1. Public Methods:

// In Activity
public void updateData(String data) { /*...*/ }

// In Fragment
((HostActivity) getActivity()).updateData("New data");

2. Interface Callbacks:

// In Fragment
public interface DataListener {
    void onDataReceived(String data);
}

// In Activity
public class MainActivity implements SampleFragment.DataListener {
    @Override
    public void onDataReceived(String data) { /*...*/ }
}

Fragment Back Stack Management

Proper back stack handling:

getParentFragmentManager().beginTransaction()
    .hide(currentFragment)
    .add(R.id.container, newFragment)
    .addToBackStack(null)
    .commit();