How to inform recyclerview adapter of new item inserted into data

Question

I know that notifyItemInserted(position) is used, but in most of the examples I have seen it gets triggered with help of Click Listeners.

But in my case I want adapter to know the change and update its view when a button in another activity is pressed.

How can I achieve this?

Consider below example scenario: 1) App starts with Activity A

2) Activity A contains recyclerview

3) As Currently data is empty no items is shown in recyclerview

4) Somehow I got into Activity B

4) I updated the data and pressed Button

5) As new data is there, recyclerview is now having a single view with updated data

Answer 1

If it suits you, make a global instance of List of data model you want to update RecyclerView from.

List<DataModel> dataModelList = new ArrayList<>();

You can do this in a class extending Application class or somewhere else where you want.

Now in ActivityA

public class ActivityA extends AppCompatActivity {
    YourAdapter adapter;
    RecyclerView recyclerView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    recyclerView = (RecyclerView) findViewById(R.id.recyclerView);

    adapter = new YourAdapter(YourClassWhereYouPutDataModelList.dataModelList)
    recyclerView.setAdapter(adapter);


    @Override
    protected void onResume() {
        super.onResume();
        adapter.notifyDataSetChanged();
    }
}

Now in your ActivityB

public class ActivityA extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        findViewById(R.id.button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //your code to get value
                YourClassWhereYouPutDataModelList.dataModelList.add(YourValue);
                //Now it's up to you, either finish it using finish() or continue working
                //Whenever you go to ActivityA, RecyclerView will be updated
            }
        });
    }
}