Android Pass data extras to a fragment

Question

I m new to Android programming and I m having problems while passing an ArrayList of a Parcelable to a fragment  This is the Activity that is launched working well   where feedlist is an ArrayList of a parcelable Music   Intent in   new Intent context  ListMusicsActivity class    in putExtra  arrayMusic   feedList   activity startActivity in     The fragment Activity onCreate   method    Override protected void onCreate Bundle savedInstanceState        super onCreate savedInstanceState       setContentView R layout activitymusiclist        if savedInstanceState    null                ListMusicFragment frag   new ListMusicFragment            frag setArguments getIntent   getExtras               The Fragment code   public class ListMusicFragment extends SherlockFragment   private ArrayList lt Music gt  listMusics   new ArrayList lt Music gt     private ListView listMusic     Override public View onCreateView LayoutInflater inflater  ViewGroup container       Bundle savedInstanceState        listMusics    ArrayList lt Music gt   getArguments   getSerializable  arrayMusic        View view   inflater inflate R layout musiclistview  container  false       listMusic    ListView  view findViewById R id musicListView       listMusic setAdapter new MusicBaseAdapter getActivity    listMusics         return view        I think the problem is in the line   listMusics    ArrayList lt Music gt   getArguments   getSerializable  arrayMusic      Finally this is my Music class   public class Music implements Parcelable   private String url  private String artist  private String title  private String duration  private String info url  private String lyrics    public Music String url  String artist  String title       String duration  String lyrics  String info url        this url   url      this artist   artist      this title   title      this duration   duration      this lyrics   lyrics      this info url   info url     public Music Parcel in        url   ParcelUtils readString in       artist   ParcelUtils readString in       title   ParcelUtils readString in       duration   ParcelUtils readString in       info url   ParcelUtils readString in       lyrics   ParcelUtils readString in      public String getUrl         return url     public String getArtist         return artist     public String getTitle         return title     public String getDuration         return duration     public String getLyrics         return lyrics     public String getInfo         return info url      Override public int describeContents         return 0       Override public void writeToParcel Parcel dest  int flags        ParcelUtils writeString dest  url       ParcelUtils writeString dest  artist       ParcelUtils writeString dest  title       ParcelUtils writeString dest  duration       ParcelUtils writeString dest  lyrics       ParcelUtils writeString dest  info url      public static final Parcelable Creator lt Music gt  CREATOR        new Parcelable Creator lt Music gt           public Music createFromParcel Parcel in                return new Music in              public Music   newArray int size                return new Music size                When I run this code the problem I get is a java lang NullPointerException in the Fragment onCreateView   method  I would appreciate a lot if someone pointed me in the right direction to see where I am failing   EDIT  Problem solved  I just needed to add this line to the fragment Activity onCreate   method othwewise the getArguments   would return null    getSupportFragmentManager   beginTransaction        add android R id content  frag  commit      And add this to the fragment code    Override     public void onActivityCreated Bundle savedInstanceState        super onActivityCreated savedInstanceState        Bundle bundle   getArguments        if bundle    null                listMusics   bundle getParcelableArrayList  arrayMusic            listMusic setAdapter new MusicBaseAdapter getActivity    listMusics              where  listMusics is an ArrayList of Parcelable Music

User · Answer

I prefer Serializable   no boilerplate code  For passing data to other Fragments or Activities the speed difference to a Parcelable does not matter   I would also always provide a helper method for a Fragment or Activity  this way you always know  what data has to be passed  Here an example for your ListMusicFragment   private static final String EXTRA MUSIC LIST    music list    public static ListMusicFragment createInstance List lt Music gt  music        ListMusicFragment fragment   new ListMusicFragment        Bundle bundle   new Bundle        bundle putSerializable EXTRA MUSIC LIST  music       fragment setArguments bundle       return fragment      Override public View onCreateView                     Bundle bundle   intent getArguments        List lt Music gt  musicList    List lt Music gt  bundle getSerializable EXTRA MUSIC LIST

User · Answer

There is a simple why that I prefered to the bundle due to the no duplicate data in memory  It consists of a init public method for the fragment   private ArrayList lt Music gt  listMusics   new ArrayList lt Music gt     private ListView listMusic    public static ListMusicFragment createInstance List lt Music gt  music        ListMusicFragment fragment   new ListMusicFragment        fragment init music       return fragment     public void init List lt Music gt  music       this listMusic   music      Override public View onCreateView LayoutInflater inflater  ViewGroup container       Bundle savedInstanceState         View view   inflater inflate R layout musiclistview  container  false       listMusic    ListView  view findViewById R id musicListView       listMusic setAdapter new MusicBaseAdapter getActivity    listMusics         return view        In two words  you create an instance of the fragment an by the init method  u can call it as u want  you pass the reference of your list without create a copy by serialization to the instance of the fragment  This is very usefull because if you change something in the list u will get it in the other parts of the app and ofcourse  you use less memory

User · Answer

Two things  First I don t think you are adding the data that you want to pass to the fragment correctly  What you need to pass to the fragment is a bundle  not an intent  For example if I wanted send an int value to a fragment I would create a bundle  put the int into that bundle  and then set that bundle as an argument to be used when the fragment was created    Bundle bundle   new Bundle    bundle putInt key  value   fragment setArguments bundle     Second to retrieve that information you need to get the arguments sent to the fragment  You then extract the value based on the key you identified it with  For example in your fragment   Bundle bundle   this getArguments    if  bundle    null        int i   bundle getInt key  defaulValue       What you are getting changes depending on what you put  Also the default value is usually null but does not need to be  It depends on if you set a default value for that argument    Lastly I do not think you can do this in onCreateView  I think you must retrieve this data within your fragment s onActivityCreated method  My reasoning is as follows  onActivityCreated runs after the underlying activity has finished its own onCreate method  If you are placing the information you wish to retrieve within the bundle durring your activity s onCreate method  it will not exist during your fragment s onCreateView  Try using this in onActivityCreated and just update your ListView contents later

User · Answer

great answer by  Rarw  Try using a bundle to pass information from one fragment to another

[java] Android: Pass data(extras) to a fragment

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