![]() This is a bit tedious, but it might prove necessary at some point for legacy projects. It is certainly possible to take an app that has several activities and rewite it such that it has one activity and several fragments. In modern, Jetpack-centric app development, often we define our fragments at the outset, as part of building our UI. Third party libraries might offer fragments as part of their API, for you to use or subclass as appropriate. We will see an example of this in the next chapter, with a Google-supplied Jetpack library offering a fragment that we use directly. However, libraries can also contribute fragment implementations. Many fragments you will write yourself, just as you write your activities and other application code. Of the two, dynamic fragments are much more common. The second approach is for cases where the fragment might be swapped out for another fragment, or whether the fragment might be conditionally shown based on user input, screen size, or other criteria (“dynamic fragments”). The first approach is for cases where the fragment will always be shown (“static fragments”) by the activity. Having FragmentContainerView elements in layout resources, where you then supply the fragments to put in those containers at runtime.Where?įragments will appear on the screen where you tell them to appear. Having multiple fragments on the screen at once, perhaps to take better advantage of larger screen sizes on tablets, Chromebooks, etc.įunctionally, fragments are Java/Kotlin classes, extending from a base Fragment class.Having one activity switch between fragments based on user input.However, at that point, you can use fragments in different ways, with two main patterns being: You define a fragment, much like you might define an activity, with layouts and lifecycle methods and so on. Rather, you should think of fragments as being units of UI reuse. What?įragments are not activities, though they can be used by activities.įragments are not containers (i.e., subclasses of ViewGroup), though typically they create a ViewGroup. Here, we will apply those six questions to help frame what we are talking about with respect to fragments. In the world of journalism, the basics of any news story consist of six questions, the Five Ws and How. This chapter will cover basic uses of fragments. Jetpack specifically advocates having an app be a single activity, with fragments for each “screen” of information. While fragments are not required, Google strongly encourages their use. Over time, fragments were used in more places and for more reasons. The original vision for fragments was to make it easier to support early Android tablets, allowing you to assemble tablet-sized UIs by snapping together a bunch of phone-sized UIs that you use individually on phones. Activities will always exist, but many times we use an activity mostly as a simple container for other UI logic.Īnd, frequently, that UI logic is held in fragments. Development is moving away from using activities as the core foundation of our UI. Activities are fine, but they are fairly inflexible.
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