Why is PendingIntent used instead of a regular Intent?

PendingIntent allows you to pass an Intent to another application so that it can execute it on behalf of your application at a later time, even if your application has been closed.

Main reasons to use PendingIntent:

• Notifications: Launching an activity or service when a notification is tapped, even if the app is not active at that moment.
• Home screen widgets: Triggering an action in the app when interacting with a widget.
• Alarms and deferred tasks: Executing app code at a specific time or under certain conditions using AlarmManager.
• SMS and other broadcast receivers: Performing an action in the app upon receiving a broadcast intent.

A regular Intent is executed immediately within your app's context. PendingIntent, on the other hand, is a wrapper around an Intent that grants permission to another app to execute this Intent with the same rights as if your app performed it.

When creating a PendingIntent, you need to choose the type of component to be launched: an activity (getActivity), a service (getService), or a broadcast receiver (getBroadcast). Flags are also specified to define the behavior of the PendingIntent, such as how to handle existing intents (FLAG_UPDATE_CURRENT, FLAG_CANCEL_CURRENT).

Example of creating a PendingIntent to launch an activity:

// Create an intent to launch MainActivity
Intent intent = new Intent(context, MainActivity.class);
// Wrap the intent in a PendingIntent
// requestCode is used to identify the pending intent
// FLAG_UPDATE_CURRENT: if such a pending intent already exists, update it with new data
PendingIntent pendingIntent = PendingIntent.getActivity(
    context,
    0,
    intent,
    PendingIntent.FLAG_UPDATE_CURRENT
);