Dilemma when to use Fragments vs Activities

Question

I know that Activities are designed to represent a single screen of my application  while Fragments are designed to be reusable UI layouts with logic embedded inside of them  Until not long ago  I developed an application as it said that they should be developed  I created an Activity to represent a screen of my application and used Fragments for ViewPager or Google Maps  I rarely created a ListFragment or other UI that can be reused several times  Recently I stumbled on a project that contains only 2 Activities one is a SettingsActivity and other one is the MainActivity  The layout of the MainActivity is populated with many hidden full screen UI fragments and only one is shown  In the Activity logic there are many FragmentTransitions between the different screens of the application  What I like about this approach is that because the application uses an ActionBar  it stays intact and does not move with the screen switching animation  which is what happens with Activity switching  This give a more fluent feel to those screen transitions  So I guess what I m asking is to share your current development manner regarding this topic  I know it might look like an opinion based question at first look but I look at it as an Android design and architecture question    Not really an opinion based one  UPDATE  01 05 2014   Following this presentation by Eric Burke from Square   which I have to say is a great presentation with a lot of useful tools for android developers  And I am not related in any way to Square  http   www infoq com presentations Android-Design  From my personal experience over the past few months  I found that the best way to construct my applications is to create groups of fragments that come to represent a flow in the application and present all those fragments in one Activity  So basically you will have the same number of Activities in your application as the number of flows  That way the action bar stays intact on all the flow s screens  but is being recreated on changing a flow which makes a lot of sense  As Eric Burke states and as I have come to realize as well  the philosophy of using as few Activities as possible is not applicable for all situations because it creates a mess in what he calls the  quot God quot  activity

User · Answer

An Activity is a user interface component that are mainly used to construct a single screen of application, and represents the main focus of attention on a screen.

In contrast, Fragments, introduced in Honeycomb(3.0) as tablets emerged with larger screens, are reusable components that are attached to and displayed within activities.

Fragments must be hosted by an activity and an activity can host one or more fragments at a time. And a fragment’s lifecycle is directly affected by its host activity’s lifecycle.

While it’s possible to develop a UI only using Activities, this is generally a bad idea since their code cannot later be reused within other Activities, and cannot support multiple screens. In contrast, these are advantages that come with the use of Fragments: optimized experiences based on device size and well-structured, reusable code.

User · Answer

Experts will tell you   When I see the UI  I will know whether to use an Activity or a Fragment   In the beginning this will not have any sense  but in time  you will actually be able to tell if you need Fragment or not    There is a good practice I found very helpful for me  It occurred to me while I was trying to explain something to my daughter    Namely  imagine a box which represents a screen  Can you load another screen in this box  If you use a new box  will you have to copy multiple items from the 1st box  If the answer is Yes  then you should use Fragments  because the root Activity can hold all duplicated elements to save you time in creating them  and you can simply replace parts of the box    But don t forget that you always need a box container  Activity  or your parts will be dispersed  So one box with parts inside   Take care not to misuse the box  Android UX experts advise  you can find them on YouTube  when we should explicitly load another Activity  instead to use a Fragment  like when we deal with the Navigation Drawer which has categories   Once you feel comfortable with Fragments  you can watch all their videos  Even more they are mandatory material    Can you right now look at your UI and figure out if you need an Activity or a Fragment  Did you get a new perspective  I think you did

User · Answer

Since Jetpack  Single-Activity app is the preferred architecture  Usefull especially with the Navigation Architecture Component   source

User · Answer

Well  according to Google s lectures  maybe here  I don t remember    you should consider using Fragments whenever it s possible  as it makes your code easier to maintain and control   However  I think that on some cases it can get too complex  as the activity that hosts the fragments need to navigate communicate between them   I think you should decide by yourself what s best for you  It s usually not that hard to convert an activity to a fragment and vice versa   I ve created a post about this dillema here  if you wish to read some further

User · Answer

Why I prefer Fragment over Activity in ALL CASES    Activity is expensive  In Fragment  views and property states are separated - whenever a fragment is in backstack  its views will be destroyed  So you can stack much more Fragments than Activity  Backstack manipulation  With FragmentManager  it s easy to clear all the Fragments  insert more than on Fragments and etcs  But for Activity  it will be a nightmare to manipulate those stuff  A much predictable lifecycle  As long as the host Activity is not recycled  the Fragments in the backstack will not be recycled  So it s possible to use FragmentManager  getFragments   to find specific Fragment  not encouraged

User · Answer

I use Fragments for better user experience  For example if you have a Button and you want to run let s say a webservice when you click it  I attach a Fragment to the parent Activity    if  id    R id forecast         ForecastFragment forecastFragment   new ForecastFragment        FragmentManager fm   getSupportFragmentManager        FragmentTransaction ft   fm beginTransaction        ft replace R id main content  forecastFragment       ft addToBackStack  backstack        forecastFragment setArguments b       ft commit        In that way the user won t have to move in another activity   And secondly I prefer Fragments because you can handle them easily during rotation

User · Answer

Almost always use fragments  If you know that the app you are building will remain very small  the extra effort of using fragments may not be worth it  so they can be left out  For larger apps  the complexity introduced is offset by the flexibility fragments provide  making it easier to justify having them in the project  Some people are very opposed to the additional complexity involved with fragments and their lifecycles  so they never use them in their projects  An issue with this approach is that there are several APIs in Android that rely on fragments  such as ViewPager and the Jetpack Navigation library  If you need to use these options in your app  then you must use fragments to get their benefits  Excerpt From  Kristin Marsicano     Android Programming  The Big Nerd Ranch Guide  4th Edition     Apple Books

User · Answer

There s more to this than you realize  you have to remember than an activity that is launched does not implicitly destroy the calling activity  Sure  you can set it up such that your user clicks a button to go to a page  you start that page s activity and destroy the current one  This causes a lot of overhead  The best guide I can give you is      Start a new activity only if it makes sense to have the main activity and this one open at the same time  think of multiple windows    A great example of when it makes sense to have multiple activities is Google Drive  The main activity provides a file explorer  When a file is opened  a new activity is launched to view that file  You can press the recent apps button which will allow you to go back to the browser without closing the opened document  then perhaps even open another document in parallel to the first

User · Answer

In my opinion it s not really relevant  The key factor to consider is    how often are you gonna reuse parts of the UI  menus for example    is the app also for tablets    The main use of fragments is to build multipane activities  which makes it perfect for Tablet Phone responsive apps

User · Answer

Don t forget that an activity is application s block component which can be shared and started through Intent  So each activity in your application should solve only one kind of task  If you have only one task in your application then I think you need only one activity and many fragments if needed  Of course you can reuse fragments in future activities which solve another tasks  This approach will be clear and logical separation of tasks  And you no need to maintain one activity with different intent filter parameters for different sets of fragments  You define tasks at the design stage of the development process based on requirements

User · Answer

use one activity per application to provide base for fragment  use fragment for screen    fragments are lite weight as compared to activites fragments are reusable  fragments are better suited for app which support both phone  amp  tablet

User · Answer

It depends what you want to build really  For example the navigation drawer uses fragments  Tabs use fragments as well  Another good implementation is where you have a listview  When you rotate the phone and click a row the activity is shown in the remaining half of the screen  Personally I use fragments and fragment dialogs as it is more professional  Plus they are handled easier in rotation

User · Answer

You are free to use one of those   Basically  you have to evaluate which is the best one to your app  Think about how you will manage the business flow and how to store manage data preferences   Think about  how Fragments store garbage data  When you implement the fragment  you have a activity root to fill with fragment s   So  if your trying to implement a lot of activities with too much fragments  you have to consider performance on your app  coz you re manipulating  coarsely speaks  two context lifecycle  remember the complexity   Remember  should I use fragments  Why shouldn t I   regards

User · Answer

My philosophy is this   Create an activity only if it s absolutely absolutely required  With the back stack made available for committing bunch of fragment transactions  I try to create as few activities in my app as possible  Also  communicating between various fragments is much easier than sending data back and forth between activities   Activity transitions are expensive  right  At least I believe so - since the old activity has to be destroyed paused stopped  pushed onto the stack  and then the new activity has to be created started resumed   It s just my philosophy since fragments were introduced

User · Answer

Thing I did  Using less fragment when possible  Unfortunately  it s possible in almost case  So  I end up with a lot of fragments and a little of activities  Some drawbacks I ve realized     ActionBar  amp  Menu  When 2 fragment has different title  menu  that    will hard to handle  Ex  when adding new fragment  you can change action bar title  but when pop it from backstack there is no way to restore the old title  You may need an Toolbar in every fragment for this case  but let believe me  that will spend you more time     When we need startForResult  activity has but fragment hasn t  Don t have transition animation by default   My solution for this is using an Activity to wrap a fragment inside  So we have separate action bar  menu  startActivityForResult  animation

User · Answer

The one big advantage of a fragment over activity is that   the code which is used for fragment can be used for different activities  So  it provides re-usability of code in application development

[android] Dilemma: when to use Fragments vs Activities:

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