Overview of Lifecycle-Aware Components

Introduction

Android UI controllers, such as activities and fragments, have a well-defined lifecycle, and their associated events are triggered during the lifecycle of the UI controller. While developing an application, it’s common practice to perform actions for dependent services and components in these lifecycles. Over time, these make the code cluttered and difficult to manage.

Recently, Google introduced the AndroidX lifecycle package to tackle this problem. This package provides interfaces that can be used to build components whose behavior can be modified based on the state of the parent UI controller.

In this lesson, we’ll learn about some key concepts to build lifecycle-aware components.

Lifecycle observer

The lifecycle of any UI component is comprised of events and states.

• Event refers to the callback methods dispatched by the Android framework during the lifecycle of a component. For example, when an activity is created, the onCreate event callback is triggered, or when the activity is paused, the onPause event callback is triggered.
• State refers to the different possible states of the UI component during its lifecycle. For example, an activity can be in an initialized, paused, or destroyed state.

Now that we understand these terms, let’s learn how we can define a lifecycle observer. We can implement the DefaultLifecycleObserver interface to override the lifecycle events in our class component. For example, let’s assume we have a component with a counter whose value can be incremented or decremented. We want to reset the counter every time the parent UI component is paused. To achieve this behavior, we can override the onPause method in our class component.