Finish all previous activities

Signals among activities

Sometimes you might want to wipe the slate due to an event, say a user decides to sign out. Here, Intent.FLAG_ACTIVITY_CLEAR_TOP works with Intent.EXTRA to allow all activities to handle the logout intent:

Intent logoutIntent = new Intent(context, HomeActivity.class);
logoutIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
logoutIntent.putExtra("LOGOUT", true); // Tag, you're it!
startActivity(logoutIntent);
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Meanwhile, HomActivity's onNewIntent method scans for the logout signal:

@Override
protected void onNewIntent(Intent intent) {
    super.onNewIntent(intent);
    if (intent.getBooleanExtra("LOGOUT", false)) {
        finish();  // Sayonara!
        startActivity(new Intent(this, LoginActivity.class)); // Welcome back, stranger!
    }
}
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This is like telling HomeActivity to pack up and go back to the login screen.

Android version variations

For signing out, it's common to use finishAffinity() to end the whole task, making sure no activities are left hanging around like awkward dinner guests:

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
    finishAffinity(); // See ya later, alligator!
} else {
    ActivityCompat.finishAffinity(this); // Old-school send-off
}


Mastering the stack and task dance

It's crucial to ensure all activities are in the same task for FLAG_ACTIVITY_CLEAR_TOP to work right. Mixing tasks is like stirring up a cocktail of unpredictable behaviors in the back stack. For scenarios where tasks might be mixed or an activity must be relocated to the top of an existing stack, you can whip up this concoction: FLAG_ACTIVITY_CLEAR_TOP | FLAG_ACTIVITY_NEW_TASK.

Exit plan for nested activities

For effectively steering nested activities, design a custom exit signal. This becomes handy when wrestling with deep hierarchies in your application:

// Within a nested activity lost deep inside your app:
Intent exitIntent = new Intent(context, HomeActivity.class);
exitIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
exitIntent.putExtra("EXIT", true); // Abandon ship!
startActivity(exitIntent);
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Upon receiving this custom bat signal, HomeActivity can dutifully finish itself and perform any required cleaning routines.

Special considerations

Handling the unexpected

Just a heads up! When using clear top with single or multiple instances of activities, note that FLAG_ACTIVITY_SINGLE_TOP will avoid creating a new instance if the target activity is already at the top. But sometimes, life (and you) might want something else. For such moments, isTaskRoot() helps check if the activity is the root of a task.

The influence of launch modes

Different launch modes in your AndroidManifest.xml like singleTop, singleTask, or singleInstance can change the game for flags like FLAG_ACTIVITY_CLEAR_TOP. Always stay aware of your activity launch modes.

Intermediary activities

What about those middling activities which aren't at the top, nor at the bottom but need to perform specific exit operations? For such cases, broadcasting a custom exit intent might just be your knight in shining armor.