livedata

LiveData is an observable data holder class from Android Jetpack that is designed to hold a value and propagate changes to its observers. It is commonly used within the MVVM architecture to expose data from a ViewModel to the UI.

A defining feature of LiveData is its lifecycle awareness. Observers must be bound to a LifecycleOwner, such as an Activity or Fragment, and LiveData delivers updates only when the owner is in an Active state (STARTED or RESUMED). This helps prevent memory leaks and unnecessary work when the UI is not visible. When a lifecycle owner becomes active, it receives the latest value if one is available.

In typical usage, a ViewModel holds a private MutableLiveData<T> and exposes a public LiveData<T>. UI components observe this LiveData, using the view’s lifecycle as the bound owner. Updates are posted via setValue on the main thread or postValue from a background thread, ensuring thread-safe delivery to observers.

LiveData supports transformations and composition. Transformations.map and Transformations.switchMap provide derived data streams, and MediatorLiveData can observe multiple sources and merge them into a single output. These tools enable reactive and modular data flows within an app.

Limitations include that LiveData does not fetch data by itself and is not a persistence mechanism. It does not automatically survive process death. For persistence or complex data handling, LiveData is typically used in conjunction with repositories, databases such as Room, and other data sources.