Best practice for instantiating a new Android Fragment

Question

I have seen two general practices to instantiate a new Fragment in an application   Fragment newFragment   new MyFragment      and  Fragment newFragment   MyFragment newInstance      The second option makes use of a static method newInstance   and generally contains the following method   public static Fragment newInstance          MyFragment myFragment   new MyFragment        return myFragment      At first  I thought the main benefit was the fact that I could overload the newInstance   method to give flexibility when creating new instances of a Fragment - but I could also do this by creating an overloaded constructor for the Fragment   Did I miss something   What are the benefits of one approach over the other  Or is it just good practice

User · Answer

I m lately here  But somethings I just known that might help you a bit   If you are using Java  there is nothing much to change  But for kotlin developers  here is some following snippet I think that can make you a basement to run on    Parent fragment    inline fun  lt reified T   SampleFragment gt  newInstance text  String   T       return T  class java newInstance   apply           arguments   Bundle   also   it putString  key text arg   text               Normal call   val f  SampleFragment   SampleFragment newInstance  ABC      or val f   SampleFragment newInstance lt SampleFragment gt   ABC      You can extend the parent init operation in child fragment class by    fun newInstance    ChildSampleFragment       val child   UserProfileFragment newInstance lt ChildSampleFragment gt   XYZ          Do anything with the current initialized args bundle here        with child arguments            return child      Happy coding

User · Answer

Best way to instantiate the fragment is use default Fragment instantiate method or create factory method to instantiate the the fragment  Caution  always create one empty constructor in fragment other while restoring fragment memory will throw run-time exception

User · Answer

use this code 100  fix your problem  enter this code in firstFragment  public static yourNameParentFragment newInstance          Bundle args   new Bundle        args putBoolean  yourKey  yourValue       YourFragment fragment   new YourFragment        fragment setArguments args       return fragment      this sample send boolean data  and in SecendFragment  yourNameParentFragment name  yourNameParentFragment newInstance       Bundle bundle     bundle sellDiamondFragments2 getArguments      boolean a  bundle getBoolean  yourKey         must value in first fragment is static   happy code

User · Answer

The only benefit in using the newInstance   that I see are the following    You will have a single place where all the arguments used by the fragment could be bundled up and you don t have to write the code below everytime you instantiate a fragment   Bundle args   new Bundle    args putInt  someInt   someInt   args putString  someString   someString      Put any other arguments myFragment setArguments args    Its a good way to tell other classes what arguments it expects to work faithfully though you should be able to handle cases if no arguments are bundled in the fragment instance     So  my take is that using a static newInstance   to instantiate a fragment is a good practice

User · Answer

If Android decides to recreate your Fragment later  it s going to call the no-argument constructor of your fragment  So overloading the constructor is not a solution   With that being said  the way to pass stuff to your Fragment so that they are available after a Fragment is recreated by Android is to pass a bundle to the setArguments method   So  for example  if we wanted to pass an integer to the fragment we would use something like   public static MyFragment newInstance int someInt        MyFragment myFragment   new MyFragment         Bundle args   new Bundle        args putInt  someInt   someInt       myFragment setArguments args        return myFragment      And later in the Fragment onCreate   you can access that integer by using   getArguments   getInt  someInt   0     This Bundle will be available even if the Fragment is somehow recreated by Android   Also note  setArguments can only be called before the Fragment is attached to the Activity   This approach is also documented in the android developer reference  https   developer android com reference android app Fragment html

User · Answer

You can use smth like this  val fragment   supportFragmentManager fragmentFactory instantiate classLoader  YourFragment  class java name   because this answer now is Deprecated

User · Answer

Since the questions about best practice  I would add  that very often good idea to use hybrid approach for creating fragment when working with some REST web services  We can t pass complex objects  for example some User model  for case of displaying user fragment  But what we can do  is to check in onCreate that user  null and if not - then bring him from data layer  otherwise - use existing   This way we gain both ability to recreate by userId in case of fragment recreation by Android and snappiness for user actions  as well as ability to create fragments by holding to object itself or only it s id  Something likes this   public class UserFragment extends Fragment       public final static String USER ID  user id       private User user      private long userId        Override     public void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           userId   getArguments   getLong USER ID           if user  null                                 Recreating here user from user id i e requesting from your data model                 which could be services  direct request to rest  or data layer sitting                on application model                             user   bringUser                         public static UserFragment newInstance User user  long user id           UserFragment userFragment   new UserFragment            Bundle args   new Bundle            args putLong USER ID user id           if user  null               userFragment user user                    userFragment setArguments args           return userFragment              public static UserFragment newInstance long user id           return newInstance null user id              public static UserFragment newInstance User user           return newInstance user user id

User · Answer

While  yydl gives a compelling reason on why the newInstance method is better      If Android decides to recreate your Fragment later  it s going to call   the no-argument constructor of your fragment  So overloading the   constructor is not a solution    it s still quite possible to use a constructor  To see why this is  first we need to see why the above workaround is used by Android   Before a fragment can be used  an instance is needed  Android calls YourFragment    the no arguments constructor  to construct an instance of the fragment  Here any overloaded constructor that you write will be ignored  as Android can t know which one to use    In the lifetime of an Activity the fragment gets created as above and destroyed multiple times by Android  This means that if you put data in the fragment object itself  it will be lost once the fragment is destroyed   To workaround  android asks that you store data using a Bundle  calling setArguments     which can then be accessed from YourFragment  Argument bundles are protected by Android  and hence are guaranteed to be persistent   One way to set this bundle is by using a static newInstance method   public static YourFragment newInstance  int data        YourFragment yf   new YourFragment          See this code gets executed immediately on your object construction        Bundle args   new Bundle        args putInt  data   data       yf setArguments args       return yf      However  a constructor   public YourFragment int data        Bundle args   new Bundle        args putInt  data   data       setArguments args       can do exactly the same thing as the newInstance method   Naturally  this would fail  and is one of the reasons Android wants you to use the newInstance method   public YourFragment int data        this data   data     Don t do this     As further explaination  here s Android s Fragment Class          Supply the construction arguments for this fragment   This can only    be called before the fragment has been attached to its activity  that    is  you should call it immediately after constructing the fragment   The    arguments supplied here will be retained across fragment destroy and    creation      public void setArguments Bundle args        if  mIndex  gt   0            throw new IllegalStateException  Fragment already active              mArguments   args      Note that Android asks that the arguments be set only at construction  and guarantees that these will be retained   EDIT  As pointed out in the comments by  JHH  if you are providing a custom constructor that requires some arguments  then Java won t provide your fragment with a no arg default constructor  So this would require you to define a no arg constructor  which is code that you could avoid with the newInstance factory method   EDIT  Android doesn t allow using an overloaded constructor for fragments anymore  You must use the newInstance method

User · Answer

There is also another way   Fragment instantiate context  MyFragment class getName    myBundle

User · Answer

setArguments   is useless  It only brings a mess   public class MyFragment extends Fragment        public String mTitle      public String mInitialTitle       public static MyFragment newInstance String param1            MyFragment f   new MyFragment            f mInitialTitle   param1          f mTitle   param1          return f              Override     public void onSaveInstanceState Bundle state            state putString  mInitialTitle   mInitialTitle           state putString  mTitle   mTitle           super onSaveInstanceState state               Override     public View onCreateView LayoutInflater inflater  ViewGroup container  Bundle state            if  state    null                mInitialTitle   state getString  mInitialTitle                mTitle   state getString  mTitle

User · Answer

Some kotlin code   companion object       fun newInstance first  String  second  String    SampleFragment           return SampleFragment   apply               arguments   Bundle   apply                   putString  firstString   first                  putString  secondString   second                                    And you can get arguments with this   val first  String by lazy   arguments  getString  firstString       default   val second  String by lazy   arguments  getString  secondString       default

User · Answer

Best practice to instance fragments with arguments in android is to have static factory method in your fragment   public static MyFragment newInstance String name  int age        Bundle bundle   new Bundle        bundle putString  name   name       bundle putInt  age   age        MyFragment fragment   new MyFragment        fragment setArguments bundle        return fragment      You should avoid setting your fields with the instance of a fragment  Because whenever android system recreate your fragment  if it feels that the system needs more memory  than it will recreate your fragment by using constructor with no arguments   You can find more info about best practice to instantiate fragments with arguments here

User · Answer

I disagree with yydi answer saying      If Android decides to recreate your Fragment later  it s going to call   the no-argument constructor of your fragment  So overloading the   constructor is not a solution    I think it is a solution and a good one  this is exactly the reason it been developed by Java core language    Its true that Android system can destroy and recreate your Fragment  So you can do this   public MyFragment         An empty constructor for Android System to use  otherwise exception may occur     public MyFragment int someInt        Bundle args   new Bundle        args putInt  someInt   someInt       setArguments args       It will allow you to pull someInt from getArguments   latter on  even if the Fragment been recreated by the system  This is more elegant solution than static constructor   For my opinion static constructors are useless and should not be used  Also they will limit you if in the future you would like to extend this Fragment and add more functionality to the constructor  With static constructor you can t do this   Update   Android added inspection that flag all non-default constructors with an error  I recommend to disable it  for the reasons mentioned above

User · Answer

I believe I have a much simpeler solution for this   public class MyFragment extends Fragment      private String mTitle     private List lt MyObject gt  mObjects      public static MyFragment newInstance String title  List lt MyObject gt  objects     MyFragment myFrag   new MyFragment       myFrag mTitle   title     myFrag mObjects   objects     return myFrag

[android] Best practice for instantiating a new Android Fragment

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