Is it necessary to declare a BroadcastReceiver in the Android manifest file?

Declaring a BroadcastReceiver in the Android manifest is not always necessary. If you want your BroadcastReceiver to respond to system or global events even when the app is not running, then it should be registered in the manifest using the <receiver> tag.

However, if the BroadcastReceiver is used only within the app and should only operate while the app is active, it can be registered dynamically in code using registerReceiver(). This approach is often used for local or temporary events.

Example of dynamic registration:

BroadcastReceiver receiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        // handle event
    }
};

// Registration
context.registerReceiver(receiver, new IntentFilter("ACTION_NAME"));

// Unregistration
context.unregisterReceiver(receiver);

In summary: declare in the manifest if the receiver needs to operate constantly and respond to system broadcast messages; otherwise, dynamic registration is sufficient.