Here is a concise answer to the question "When to use Fragments vs Activities in Android?":
Activities are the main building blocks of an Android app, representing a single screen with a user interface. They are responsible for managing the UI, handling user input, and orchestrating the app's lifecycle events[1][2][3]. Activities are typically used as the top-level components of an app's structure[2].
Fragments, on the other hand, are reusable pieces of UI that can be embedded within Activities. They have their own lifecycle, UI, and behavior[1][2][3]. Fragments are useful in the following scenarios:
When you want to create modular, reusable components for your UI[2]
When you need to adapt to different screen sizes and orientations[2]
To build dynamic and flexible interfaces, especially on tablets with larger screens[3]
To break down a complex UI into smaller, more manageable pieces[3]
In many cases, a combination of Activities and Fragments is the best approach[2]. Activities serve as the entry points to your app, while Fragments provide the building blocks for creating complex UIs within those Activities[2].
