FRAGMENT LIFECYCLE HOW TO
FRAGMENT LIFECYCLE ANDROID

onPause: Called when the system is about to start resuming another activity.At that moment this activity is already at the top of the activity stack and is visible to the user. onResume: It always runs before the application appears to the user.onStart: This method is always executed right after the onCreate and whenever the activity returns from background to foreground through onRestart.onCreate(activities) / onCreateView(fragments): The only required method (that is, it needs to be overwritten by the class that extends Activity) defines what the layout of that activity is (with the 'setContentView' method) and where the XML components are mapped to the code.So let's put together all this information: In this case, if we call this activity again, as it was destroyed, then it will start its flow from the onCreate because it needs to be re-created and added again in the stack.

Now when we enter the background (we pressed home or another activity entered in front of it) it goes to the onStop method and when it comes back to the foreground it executes the onRestart methods and then the onStart and onResume normally, since it was only in the background and does not need to be re-created.Īnd finally when the activity is destroyed, for any reason (for example, pressing the back button) it follows the following flow: onStop and onDestroy in which all the resources of this activity are released and it exits the system activity stack. After that it will go through the onStart and soon after the 'onResume', in which the activity is already visible on the screen. When an activity is coming to the foreground and becoming visible to the user, it goes through the onCreate method that creates the activity layout, from the XML.

The only mandatory callback that we should override is onCreate for the activity and onCreateView for fragment, because we define the layout and do the mapping of the UI components inside of them. But what is the correct execution order, and which ones do we need to implement? In the image we can see a lot of callbacks. The following image compares both lifecycles: on the left, the activity, and on the right, the fragment: The fragment lifecycle is embedded within the activity lifecycle but has some details and extra steps in it. Within this, you can handle when the activity is destroyed, paused, resumed, or created. When an application is opened and shows its first activity, it follow a specific lifecycle. The fragment's lifecycle is directly affected by the host activity's lifecycle - in other words, a fragment cannot be instantiated alone! And it must always be embedded in an activity. You can think of a fragment as a modular section of an activity, which has its own lifecycle, receives its own input events, and to which you can add or remove while the activity is running (sort of like a 'sub activity' that you can reuse in different activities). You can combine multiple fragments in a single activity to build a multi-pane UI and reuse a fragment in multiple activities.

Fragment represents a behavior or a portion of user interface in an Activity.

FRAGMENT LIFECYCLE HOW TO

(UI components and how to build a layout will be discussed in another article). In other words, it is responsible for creating a window to hold your UI components. Activity is the part where the user will interacts with your application.

FRAGMENT LIFECYCLE ANDROID

In this first article we will talk about activities, fragments, show example codes, and look at the lifecycle of the Android application. Android's user interface is mainly based on direct manipulation, using touch gestures that loosely correspond to real-world actions, such as swiping, tapping and pinching, to manipulate on-screen objects, along with a virtual keyboard for text input.'Īs the most of you know, the Android system runs its features using applications. 'Android is a mobile operating system developed by Google, based on the Linux kernel and designed primarily for touchscreen mobile devices such as smartphones and tablets. Let's start with a little history: What is Android? In this collection of articles about Android, I will guide you through the basic topics that you'll need to get started in this mobile world - even if you're completely new to the Android operating system.

Fragment lifecycle