将列表从“主要活动”传递到选项卡Fragment RecyclerView

Question

I have activity which have 4 tabs and each tab has RecyclerView . I fetch Json data in MainActivity and then convert it into a List.

The challenge here is to pass the list to each RecyclerView in each Fragment in each tab.

Answer 1

Simplest way would be using ViewModel like this:

ViewModel:

public class SharedViewModel extends ViewModel {
    private List<Item> list_1= ArrayList<Item>();
    private List<Item> list_2= ArrayList<Item>();

    public void setList_1(List<Item> list) {
        list_1 = list
    }

    public List<Item> getList_1() {
        return list_1 ;
    }

    public void setList_2(List<Item> list) {
        list_2 = list
    }

    public List<Item> getList_2() {
        return list_2 ;
    }
}

MainActivity:

public class MainActivity extends AppCompatActivity {

    SharedViewModel model;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_acticity);
        model = ViewModelProviders.of(this).get(SharedViewModel.class);

        // Getting your lists here
        model.setList_1(list_1);
        model.setList_2(list_2);

    }
}

Fragment_1:

public class Fragment_1 extends Fragment {

    private SharedViewModel model;
    List<Item> list_1 = new ArrayList<>();

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
        list_1 = model.getList_1();
    }
}

Fragment_2:

public class Fragment_2 extends Fragment {

    private SharedViewModel model;
    List<Item> list_2 = new ArrayList<>();

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
        list_2 = model.getList_2();
    }
}

But, better way is more complex. More info here Guide to App Architecture

Answer 2

You might consider using a BoradcastReceiver in your Fragment . So when the lists for the fragments are updated, you send a broadcast from your MainActivity and the broadcast will be received in the Fragments.

You just have to register BroadcastReceiver in your Fragment like this.

private BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        // Get extra data included in the Intent
        // You might consider sending a list to be passed to the adapter of the RecyclerView. 
        String data = intent.getStringExtra("data");
        // Update your RecyclerView with data. 
    }
};

Register the receiver in the Fragment inside your onResume function.

@Override
protected void onResume() {
    // Register to receive messages.
    // We are registering an observer (mMessageReceiver) to receive Intents
    // with actions named "update-frag-1-recyclerview".
    LocalBroadcastManager.getInstance(this).registerReceiver(
            mMessageReceiver, new IntentFilter("update-frag-1-recyclerview"));
    super.onResume();
}

And un-register the receiver in onPause function in your Fragment .

@Override
protected void onPause() {
    // Unregister since the Fragment is paused.
    LocalBroadcastManager.getInstance(this).unregisterReceiver(
            mMessageReceiver);
    super.onPause();
}

Now from your Activity when the data is received and you are now ready to pass the data to your fragments, just send the broadcasts accordingly to be received by your fragments. I am showing one.

Intent intent = new Intent("update-frag-1-recyclerview");
// You can also include some extra data.
intent.putExtra("data", "This is some data!");
LocalBroadcastManager.getInstance(this).sendBroadcast(intent);

This will trigger the onReceive function in your Fragment1 as you are listening to the event which is update-frag-1-recyclerview from Fragment1 . You can do the same thing for other fragments as well. Keep in mind that I am only sending just one data which is String . You might consider sending a list as well as an extra along with the intent to be received in the Fragment .

Hope that helps!