Fragments in Android are a modular part of an Activity that represents a portion of the User Interface (UI) on the screen. They provide flexibility in designing UI layouts that can adapt to different screen sizes and orientations.
Fragments are tightly linked to their host Activity’s lifecycle. They can only exist within an Activity and their lifecycle is directly affected by the lifecycle of the hosting Activity. This means that if the hosting Activity is paused, the Fragment’s methods and operations related to that Activity will also be paused.
One of the advantages of using Fragments is their dynamic nature. They can be added, removed, or replaced dynamically while the Activity is running. This allows for dynamic UI changes and better adaptability of the application based on user interactions or changes in device orientation.
By using Fragments, developers can create modular and reusable components of the UI, making it easier to manage and update different sections of the application’s interface. It also allows for better code organization and separation of concerns.
Types of Android Fragments
There are three main types of Android fragments:
- Single-frame Fragments: These fragments are used to display a single view on the screen. They are typically used for handheld devices, such as smartphones.
- List Fragments: These fragments are used to display a list of items on the screen. They are typically used for tablets and other larger devices.
- Fragment Transactions: These fragments are used to transition between different fragments. They can be used to create a variety of effects, such as adding, removing, and replacing fragments.
Fragment Lifecycle in Android:
Here is an overview of the Fragment lifecycle:
This method is called when the Fragment is first created. It is typically used for initializing essential components and setting up the Fragment’s state.
In this method, you inflate the Fragment’s layout and initialize its user interface. It returns the root View of the Fragment, which will be displayed on the screen.
This method is called after the onCreateView() method. It is often used for further initialization of the Fragment’s user interface elements, such as setting up listeners or accessing the inflated Views.
This callback is invoked when the Fragment becomes visible to the user. At this point, the Fragment is in the foreground and can start interacting with the user.
onResume() is called when the Fragment gains focus and becomes active. It is the appropriate place to start animations, acquire resources, or resume ongoing tasks.
When the Fragment loses focus, the onPause() method is called. It is used to pause or release any resources that are no longer needed while the Fragment is not visible.
This callback is invoked when the Fragment is no longer visible to the user. It indicates that the Fragment is going into the background and should stop any ongoing operations or releases resources.
When the Fragment is being destroyed, onDestroyView() is called. It allows you to clean up resources associated with the Fragment’s View hierarchy.
This method is called before the Fragment is completely destroyed. It is typically used for releasing any remaining resources or performing final cleanup tasks.
onDetach() is called when the Fragment is detached from its hosting Activity. It signifies the end of the Fragment’s lifecycle.
This method is called before the Fragment is destroyed to allow it to save any dynamic data that needs to persist across configuration changes (such as screen rotation). You can save data in a Bundle object and retrieve it later in the onCreate() or onCreateView() methods.
After the Fragment is recreated following a configuration change, the onViewStateRestored() method is called. It allows you to retrieve any saved state from the Bundle and restore the Fragment’s previous state.
This callback is called after the hosting Activity’s onCreate() method has completed. It is commonly used for communication between the Fragment and its parent Activity, such as retrieving references to Activity-level objects or setting up callbacks.
This method is invoked when the visibility of the Fragment changes. It is primarily used when working with ViewPager or FragmentPagerAdapter to determine when a Fragment becomes visible or hidden to the user.
onAttach() is called when the Fragment is associated with its hosting Activity. It provides you with a reference to the Activity, which you can use to communicate with the Activity or access its methods and data.
By calling setRetainInstance(true) in the Fragment’s onCreate() method, you can retain the Fragment instance across configuration changes. This means the Fragment will not be destroyed and recreated but will retain its state.
It’s important to note that the Fragment lifecycle is closely tied to the hosting Activity’s lifecycle. Fragments may go through their lifecycle multiple times if they are added, removed, or replaced within the Activity. Properly managing the Fragment lifecycle is crucial for maintaining a stable and responsive user interface.