Communicating between a fragment and an activity - best practices

Question

This question is mostly to solicit opinions on the best way to handle my app   I have three fragments being handled by one activity   Fragment A has one clickable element the photo and Fragment B has 4 clickable elements the buttons   The other fragment just displays details when the photo is clicked   I am using ActionBarSherlock       The forward and back buttons need to change the photo to the next or previous poses  respectively   I could keep the photo and the buttons in the same fragment  but wanted to keep them separate in case I wanted to rearrange them in a tablet     I need some advice - should I combine Fragments A and B   If not  I will need to figure out how to implement an interface for 3 clickable items     I considered using Roboguice  but I am already extending using SherlockFragmentActivity so that s a no go   I saw mention of Otto  but I didn t see good tutorials on how to include in a project  What do you think best design practice should be     I also need help figuring out how to communicate between a fragment and an activity   I d like to keep some data  global  in the application  like the pose id   Is there some example code I can see besides the stock android developer s information   That is not all that helpful     BTW  I m already storing all the information about each pose in a SQLite database   That s the easy part

User · Accepted Answer

The easiest way to communicate between your activity and fragments is using interfaces. The idea is basically to define an interface inside a given fragment A and let the activity implement that interface.

Once it has implemented that interface, you could do anything you want in the method it overrides.

The other important part of the interface is that you have to call the abstract method from your fragment and remember to cast it to your activity. It should catch a ClassCastException if not done correctly.

There is a good tutorial on Simple Developer Blog on how to do exactly this kind of thing.

I hope this was helpful to you!

User · Answer

It is implemented by a Callback interface            First of all  we have to make an interface    public interface UpdateFrag        void updatefrag           In the Activity do the following code    UpdateFrag updatfrag    public void updateApi UpdateFrag listener            updatfrag   listener         from the event from where the callback has to fire in the Activity    updatfrag updatefrag         In the Fragment implement the interface in CreateView do the   following code       Home getActivity    updateApi new UpdateFrag              Override         public void updatefrag                        your stuff

User · Answer

The suggested method for communicating between fragments is to use callbacks listeners that are managed by your main Activity   I think the code on this page is pretty clear  http   developer android com training basics fragments communicating html  You can also reference the IO 2012 Schedule app  which is designed to be a de-facto reference app   It can be found here  http   code google com p iosched   Also  here is a SO question with good info  How to pass data between fragments

User · Answer

There are severals ways to communicate between activities  fragments  services etc  The obvious one is to communicate using interfaces  However  it is not a productive way to communicate  You have to implement the listeners etc   My suggestion is to use an event bus  Event bus is a publish subscribe pattern implementation   You can subscribe to events in your activity and then you can post that events in your fragments etc   Here on my blog post you can find more detail about this pattern and also an example project to show the usage

User · Answer

I made a annotation library that can do the cast for you  check this out  https   github com zeroarst callbackfragment    CallbackFragment public class MyFragment extends Fragment         Callback     interface FragmentCallback          void onClickButton MyFragment fragment                 private FragmentCallback mCallback        Override     public void onClick View v            switch  v getId                  case R id bt1                 mCallback onClickButton this                   break              case R id bt2                    Because we give mandatory   false so this might be null if not implemented by the host                  if  mCallbackNotForce    null                  mCallbackNotForce onClickButton this                   break                      It then generates a subclass of your fragment  And just add it to FragmentManager   public class MainActivity extends AppCompatActivity implements MyFragment FragmentCallback         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               Toast mToast        Override     public void onClickButton MyFragment fragment            if  mToast    null              mToast cancel            mToast   Toast makeText this   Callback from     fragment getTag    Toast LENGTH SHORT           mToast show

User · Answer

I m not sure I really understood what you want to do  but the suggested way to communicate between fragments is to use callbacks with the Activity  never directly between fragments  See here http   developer android com training basics fragments communicating html

User · Answer

There is the latest techniques to communicate fragment to activity without any interface follow the steps Step 1- Add the dependency in gradle implementation  androidx fragment fragment 1 3 0-rc01

User · Answer

You can create declare a public interface with a function declaration in the fragment and implement the interface in the activity  Then you can call the function from the fragment

User · Answer

I am using Intents to communicate actions back to the main activity  The main activity is listening to these by overriding onNewIntent Intent intent   The main activity translates these actions to the corresponding fragments for example   So you can do something like this   public class MainActivity extends Activity         public static final String INTENT ACTION SHOW FOO    show foo       public static final String INTENT ACTION SHOW BAR    show bar         Override    protected void onNewIntent Intent intent            routeIntent intent           private void routeIntent Intent intent           String action   intent getAction           if  action    null                               switch  action                case INTENT ACTION SHOW FOO                     for example show the corresponding fragment                 loadFragment FooFragment                   break              case INTENT ACTION SHOW BAR                  loadFragment BarFragment                   break                                     Then inside any fragment to show the foo fragment   Intent intent   new Intent context  MainActivity class   intent setAction INTENT ACTION SHOW FOO      Prevent activity to be re-instantiated if it is already running     Instead  the onNewEvent   is triggered intent addFlags Intent FLAG ACTIVITY SINGLE TOP   Intent FLAG ACTIVITY CLEAR TOP   getContext   startActivity intent

User · Answer

To communicate between an Activity and Fragments  there are several options  but after lots of reading and many experiences  I found out that it could be resumed this way    Activity wants to communicate with child Fragment    Simply write public methods in your Fragment class  and let the Activity call them Fragment wants to communicate with the parent Activity    This requires a bit more of work  as the official Android link https   developer android com training basics fragments communicating suggests  it would be a great idea to define an interface that will be implemented by the Activity  and which will establish a contract for any Activity that wants to communicate with that Fragment  For example  if you have FragmentA  which wants to communicate with any activity that includes it  then define the FragmentAInterface which will define what method can the FragmentA call for the activities that decide to use it  A Fragment wants to communicate with other Fragment    This is the case where you get the most  complicated  situation  Since you could potentially need to pass data from FragmentA to FragmentB and viceversa  that could lead us to defining 2 interfaces  FragmentAInterface which will be implemented by FragmentB and FragmentAInterface which will be implemented by FragmentA  That will start making things messy  And imagine if you have a few more Fragments on place  and even the parent activity wants to communicate with them  Well  this case is a perfect moment to establish a shared ViewModel for the activity and it s fragments  More info here https   developer android com topic libraries architecture viewmodel   Basically  you need to define a SharedViewModel class  that has all the data you want to share between the activity and the fragments that will be in need of communicating data among them    The ViewModel case  makes things pretty simpler at the end  since you don t have to add extra logic that makes things dirty in the code and messy  Plus it will allow you to separate the gathering  through calls to an SQLite Database or an API  of data from the Controller  activities and fragments

[android] Communicating between a fragment and an activity - best practices

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