Basic communication between two fragments

Question

I have one activity - MainActivity  Within this activity I have two fragments  both of which I created declaratively within the xml    I am trying to pass the String of text input by the user into Fragment A to the text view in Fragment B  However  this is proving to be very difficult  Does anyone know how I might achieve this   I am aware that a fragment can get a reference to it s activity using getActivity    So I m guessing I would start there

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Update  Ignore this answer  Not that it doesn t work  But there are better methods available  Moreover  Android emphatically discourage direct communication between fragments  See official doc  Thanks user  Wahib Ul Haq for the tip    Original Answer  Well  you can create a private variable and setter in Fragment B  and set the value from Fragment A itself   FragmentB java  private String inputString             public void setInputString String string      inputString   string      FragmentA java    go to fragment B  FragmentB frag    new FragmentB    frag setInputString YOUR STRING     create your fragment transaction object  set animation etc fragTrans replace ITS ARGUMENTS    Or you can use Activity as you suggested in question

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Have a look at the Android developers page  http   developer android com training basics fragments communicating html DefineInterface  Basically  you define an interface in your Fragment A  and let your Activity implement that Interface  Now you can call the interface method in your Fragment  and your Activity will receive the event  Now in your activity  you can call your second Fragment to update the textview with the received value  Your Activity implements your interface  See FragmentA below   public class YourActivity implements FragmentA TextClicked       Override     public void sendText String text              Get Fragment B         FraB frag    FragB              getSupportFragmentManager   findFragmentById R id fragment b           frag updateText text             Fragment A defines an Interface  and calls the method when needed  public class FragA extends Fragment       TextClicked mCallback       public interface TextClicked          public void sendText String text               Override     public void onAttach Activity activity            super onAttach activity               This makes sure that the container activity has implemented            the callback interface  If not  it throws an exception         try               mCallback    TextClicked  activity            catch  ClassCastException e                throw new ClassCastException activity toString                       must implement TextClicked                         public void someMethod            mCallback sendText  YOUR TEXT                Override     public void onDetach             mCallback   null       gt  avoid leaking  thanks  Deepscorn         super onDetach              Fragment B has a public method to do something with the text  public class FragB extends Fragment       public void updateText String text              Here you have it

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Consider my 2 fragments A and B  and Suppose I need to pass data from B to A   Then create an interface in B  and pass the data to the Main Activity  There create another interface and pass data to fragment A   Sharing a small example   Fragment A looks like  public class FragmentA extends Fragment implements InterfaceDataCommunicatorFromActivity   public InterfaceDataCommunicatorFromActivity interfaceDataCommunicatorFromActivity  String data    Override public View onCreateView LayoutInflater inflater  ViewGroup container          Bundle savedInstanceState           TODO Auto-generated method stub     return super onCreateView inflater  container  savedInstanceState       Override public void updateData String data           TODO Auto-generated method stub     this data   data        data is updated here which is from fragment B     Override public void onAttach Activity activity           TODO Auto-generated method stub     super onAttach activity       try           interfaceDataCommunicatorFromActivity    InterfaceDataCommunicatorFromActivity  activity        catch  ClassCastException e            throw new ClassCastException activity toString                       must implement TextClicked                  FragmentB looks like  class FragmentB extends Fragment   public InterfaceDataCommunicator interfaceDataCommunicator    Override public void onCreate Bundle savedInstanceState           TODO Auto-generated method stub     super onCreate savedInstanceState           call this inorder to send Data to interface     interfaceDataCommunicator updateData  data       public interface InterfaceDataCommunicator       public void updateData String data       Override public void onAttach Activity activity           TODO Auto-generated method stub     super onAttach activity       try           interfaceDataCommunicator    InterfaceDataCommunicator  activity        catch  ClassCastException e            throw new ClassCastException activity toString                       must implement TextClicked                  Main Activity is  public class MainActivity extends Activity implements InterfaceDataCommunicator   public InterfaceDataCommunicatorFromActivity interfaceDataCommunicatorFromActivity    Override protected void onCreate Bundle savedInstanceState        super onCreate savedInstanceState       setContentView R layout activity main       Override public boolean onCreateOptionsMenu Menu menu           Inflate the menu  this adds items to the action bar if it is present      getMenuInflater   inflate R menu main  menu       return true      Override public void updateData String data           TODO Auto-generated method stub     interfaceDataCommunicatorFromActivity updateData data       public interface InterfaceDataCommunicatorFromActivity       public void updateData String data

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Take a look at https   github com greenrobot EventBus or http   square github io otto   or even     http   nerds weddingpartyapp com tech 2014 12 24 implementing-an-event-bus-with-rxjava-rxbus

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The nicest and recommended way is to use a shared ViewModel    https   developer android com topic libraries architecture viewmodel sharing  From Google doc   public class SharedViewModel extends ViewModel   private final MutableLiveData lt Item gt  selected   new MutableLiveData lt Item gt      public void select Item item        selected setValue item      public LiveData lt Item gt  getSelected         return selected        public class MasterFragment extends Fragment   private SharedViewModel model  public void onCreate Bundle savedInstanceState        super onCreate savedInstanceState       model   ViewModelProviders of getActivity    get SharedViewModel class       itemSelector setOnClickListener item - gt            model select item                 public class DetailFragment extends Fragment   public void onCreate Bundle savedInstanceState        super onCreate savedInstanceState       SharedViewModel model   ViewModelProviders of getActivity    get SharedViewModel class       model getSelected   observe this    item - gt            Update the UI                ps  two fragments never communicate directly

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Learn   setTargetFragment      Where   startActivityForResult     establishes a relationship between 2 activities    setTargetFragment     defines the caller called relationship between 2 fragments

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Some of the other examples  and even the documentation at the time of this writing  use outdated onAttach methods  Here is a full updated example     Notes   You don t want the Fragments talking directly to each other or to the Activity  That ties them to a particular Activity and makes reuse difficult  The solution is to make an callback listener interface that the Activity will implement  When the Fragment wants to send a message to another Fragment or its parent activity  it can do it through the interface  It is ok for the Activity to communicate directly to its child fragment public methods  Thus the Activity serves as the controller  passing messages from one fragment to another    Code  MainActivity java  public class MainActivity extends AppCompatActivity implements GreenFragment OnGreenFragmentListener        private static final String BLUE TAG    blue       private static final String GREEN TAG    green       BlueFragment mBlueFragment      GreenFragment mGreenFragment        Override     protected void onCreate Bundle savedInstanceState            super onCreate savedInstanceState           setContentView R layout activity main               add fragments         FragmentManager fragmentManager   getSupportFragmentManager             mBlueFragment    BlueFragment  fragmentManager findFragmentByTag BLUE TAG           if  mBlueFragment    null                mBlueFragment   new BlueFragment                fragmentManager beginTransaction   add R id blue fragment container  mBlueFragment  BLUE TAG  commit                       mGreenFragment    GreenFragment  fragmentManager findFragmentByTag GREEN TAG           if  mGreenFragment    null                mGreenFragment   new GreenFragment                fragmentManager beginTransaction   add R id green fragment container  mGreenFragment  GREEN TAG  commit                            The Activity handles receiving a message from one Fragment        and passing it on to the other Fragment      Override     public void messageFromGreenFragment String message            mBlueFragment youveGotMail message             GreenFragment java  public class GreenFragment extends Fragment        private OnGreenFragmentListener mCallback        Override     public View onCreateView LayoutInflater inflater  ViewGroup container  Bundle savedInstanceState            View v   inflater inflate R layout fragment green  container  false            Button button   v findViewById R id button           button setOnClickListener new View OnClickListener                  Override             public void onClick View v                    String message    Hello  Blue  I m Green                    mCallback messageFromGreenFragment message                                      return v                This is the interface that the Activity will implement        so that this Fragment can communicate with the Activity      public interface OnGreenFragmentListener           void messageFromGreenFragment String text                 This method insures that the Activity has actually implemented our        listener and that it isn t null       Override     public void onAttach Context context            super onAttach context           if  context instanceof OnGreenFragmentListener                mCallback    OnGreenFragmentListener  context            else               throw new RuntimeException context toString                           must implement OnGreenFragmentListener                          Override     public void onDetach             super onDetach            mCallback   null            BlueFragment java  public class BlueFragment extends Fragment        private TextView mTextView        Override     public View onCreateView LayoutInflater inflater  ViewGroup container  Bundle savedInstanceState            View v   inflater inflate R layout fragment blue  container  false           mTextView   v findViewById R id textview           return v                This is a public method that the Activity can use to communicate        directly with this Fragment     public void youveGotMail String message            mTextView setText message             XML  activity main xml   lt  xml version  1 0  encoding  utf-8   gt   lt LinearLayout     xmlns android  http   schemas android com apk res android      android layout width  match parent      android layout height  match parent      android orientation  vertical      android padding  16dp  gt        lt  -- Green Fragment container -- gt       lt FrameLayout         android id    id green fragment container          android layout width  match parent          android layout height  0dp          android layout weight  1          android layout marginBottom  16dp    gt        lt  -- Blue Fragment container -- gt       lt FrameLayout         android id    id blue fragment container          android layout width  match parent          android layout height  0dp          android layout weight  1    gt    lt  LinearLayout gt    fragment green xml   lt  xml version  1 0  encoding  utf-8   gt   lt LinearLayout xmlns android  http   schemas android com apk res android                android orientation  vertical                android background   98e8ba                android padding  8dp                android layout width  match parent                android layout height  match parent  gt        lt Button         android id    id button          android text  send message to blue          android layout width  wrap content          android layout height  wrap content   gt    lt  LinearLayout gt    fragment blue xml   lt  xml version  1 0  encoding  utf-8   gt   lt LinearLayout xmlns android  http   schemas android com apk res android                android orientation  vertical                android background   30c9fb                android padding  16dp                android layout width  match parent                android layout height  match parent  gt        lt TextView         android id    id textview          android text  TextView          android textSize  24sp          android layout width  wrap content          android layout height  wrap content   gt    lt  LinearLayout gt

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There is a simple way to implement communication between fragments of an activity using architectural components  Data can be passed between fragments of an activity using ViewModel and LiveData   Fragments involved in communication need to use the same view model objects which is tied to activity life cycle  The view model object contains livedata object to which data is passed by one fragment and the second fragment listens for changes on LiveData and receives the data sent from fragment one   For complete example see http   www zoftino com passing-data-between-android-fragments-using-viewmodel

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I recently created a library that uses annotations to generate those type casting boilerplate code for you  https   github com zeroarst callbackfragment  Here is an example  Click a TextView on DialogFragment triggers a callback to MainActivity in onTextClicked then grab the MyFagment instance to interact with   public class MainActivity extends AppCompatActivity implements MyFragment FragmentCallback  MyDialogFragment DialogListener    private static final String MY FRAGM    MY FRAGMENT   private static final String MY DIALOG FRAGM    MY DIALOG FRAGMENT     Override protected void onCreate Bundle savedInstanceState        super onCreate savedInstanceState       setContentView R layout activity main        getSupportFragmentManager   beginTransaction            add R id lo fragm container  MyFragmentCallbackable create    MY FRAGM           commit         findViewById R id bt  setOnClickListener new View OnClickListener              Override         public void onClick View v                MyDialogFragmentCallbackable create   show getSupportFragmentManager    MY DIALOG FRAGM                        Toast mToast    Override public void onClickButton MyFragment fragment        if  mToast    null          mToast cancel        mToast   Toast makeText this   Callback from     fragment getTag       to     this getClass   getSimpleName    Toast LENGTH SHORT       mToast show        Override public void onTextClicked MyDialogFragment fragment        MyFragment myFragm    MyFragment  getSupportFragmentManager   findFragmentByTag MY FRAGM       if  myFragm    null            myFragm updateText  Callback from     fragment getTag       to     myFragm getTag

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I give my activity an interface that all the fragments can then use  If you have have many fragments on the same activity  this saves a lot of code re-writing and is a cleaner solution   more modular than making an individual interface for each fragment with similar functions  I also like how it is modular  The downside  is that some fragments will have access to functions they don t need          public class MyActivity extends AppCompatActivity     implements MyActivityInterface            private List lt String gt  mData             Override         public List lt String gt  getData   return mData             Override         public void setData List lt String gt  data  mData   data               public interface MyActivityInterface            List lt String gt  getData             void setData List lt String gt  data              public class MyFragment extends Fragment             private MyActivityInterface mActivity            private List lt String gt  activityData             public void onButtonPress                  activityData   mActivity getData                        Override         public void onAttach Context context                super onAttach context               if  context instanceof MyActivityInterface                    mActivity    MyActivityInterface  context                else                   throw new RuntimeException context toString                               must implement MyActivityInterface                                      Override         public void onDetach                 super onDetach                mActivity   null

[android] Basic communication between two fragments

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