Passing data From Activity to Fragment using interface

Question

I want to pass data from an activity to a fragment, using an interface. Please have a look at the code snippets below:

Interface:

public interface FragmentCommunicator {

   public void passData(String name);
}

MainActivity:

public class MainActivity extends AppCompatActivity{

    FragmentCommunicator fragmentCommunicator;
    private Fragment fragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button b = (Button) findViewById(R.id.button);
        b.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                fragment= new Fragment();
                fragmentCommunicator = (FragmentCommunicator) getApplication();
                fragmentCommunicator.passData("hello");
                getSupportFragmentManager().beginTransaction().replace(R.id.container ,fragment).commit();

            }
        });

    }
}

Fragment:

public class Fragment extends android.support.v4.app.Fragment implements FragmentCommunicator {

    FragmentCommunicator communicator;
    Context c;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment, null);

        return view;
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        this.c = context;

    }
    @Override
    public void passData(String name) {
        Toast.makeText(c, name, Toast.LENGTH_SHORT).show();
    }
}

I just want to pass some string when I click on button, (or some other event) to launch a fragment, and when the fragment is launched, it should show a toast containing that string...

Please help any help would be appreciated.

How to pass from activity to fragment - http://stackoverflow.com/a/9245510/6254066 — AgileNinja, May 09 '16 at 16:46
@AgileNinja I said I want to pass data using interface not by bundle. — Akshay Sood, May 09 '16 at 17:27

score 10 · Accepted Answer · edited May 28 '19 at 10:43

10

Write this line of code after onCreate method.

public void passVal(FragmentCommunicator fragmentCommunicator) {
    this.fragmentCommunicator = fragmentCommunicator;
}

Something like this

public class MainActivity extends AppCompatActivity{

FragmentCommunicator fragmentCommunicator;
private Fragment fragment;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button b = (Button) findViewById(R.id.button);

    fragment= new Fragment();

    //App is crasing for this line. Working fine by removing it
    //fragmentCommunicator = (FragmentCommunicator) getApplication();

    //fragmentCommunicator.passData("hello");
    getSupportFragmentManager().beginTransaction().replace(R.id.container ,fragment).commit();

    b.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            fragmentCommunicator.passData("Hello");

        }
    });

  }

   //Here is new method
   public void passVal(FragmentCommunicator fragmentCommunicator) {
       this.fragmentCommunicator = fragmentCommunicator;

   }
}

Then write this line of code into onCreateView() of your fragment. Something like this

@Override 
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup  container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment, null);

((MainActivity) getActivity()).passVal(new FragmentCommunicator() {
       @Override
       public void passData(String name) {
           Toast.makeText(c, name, Toast.LENGTH_SHORT).show();
       }
   });
  return view;
}

Note: no need to implement FragmentCommunicator interface in your fragment. Hope it works. It works for me. I have tested

edited May 28 '19 at 10:43

Community

1
1

answered May 09 '16 at 17:57

Masum

4,879
2
23
28

from where should I start my fragment? i.e beginTransaction? – Akshay Sood May 09 '16 at 18:13
Code is updated try again. – Masum May 09 '16 at 18:18
1

java.lang.ClassCastException: android.app.Application cannot be cast to com.example.akshaysood.interfacecallback.FragmentCommunicator – Akshay Sood May 09 '16 at 18:21
Do you want to pass value by pressing any button or fragment initial time? – Masum May 09 '16 at 18:26
I want to pass the value with click on the button and at the same time the fragment should be launched – Akshay Sood May 09 '16 at 18:29
So Why are you using interface? you can do that easily with setArgument of bundle. Interface purpose is you can any time passing value to fragment from activity. its not wise in launch time – Masum May 09 '16 at 18:31
I want to know this one also – Akshay Sood May 09 '16 at 19:19
fragmentCommunicator = (FragmentCommunicator) getApplication(); What this line does? – Kanagalingam Jun 23 '18 at 13:56
This answer was helpful for setting Interfaces while using Navigation components – Ariel Oct 10 '20 at 04:35

score 1 · Answer 2 · edited May 23 '17 at 12:13

1

Activities contain fragments, you shouldn't need to pass anything. One technique would be to store your data in the activity scope and get a reference to it with getActivity().

Best practice to reference the parent activity of a fragment?

As far as the code you posted, I don't see where you call your pass data method within the fragment. I would suggest calling it in onviewcreated().

I will attempt to provide some sample code later as doing this on my mobile device is proving difficult.

Try passdata (getActivity ().someStringVariable);

edited May 23 '17 at 12:13

Community

1
1

answered May 09 '16 at 17:30

JimENewtron

83
4

how will I pass the data and access the data can you write a simple example? – Akshay Sood May 09 '16 at 17:37

score 0 · Answer 3 · answered May 09 '16 at 18:19

In your Fragment class, have a TAG field. Naming a fragment Fragment can be a bit confusing as it is the same name as an Android Fragment, so I will use ExampleFragment:

public class ExampleFragment extends android.support.v4.app.Fragment implements FragmentCommunicator {
    public static final String TAG = "ExampleFragment";

    // ...
}

Now, when you replace the fragment in the activity, make sure to pass the TAG:

getSupportFragmentManager().beginTransaction().replace(R.id.container ,fragment, ExampleFragment.TAG).commit();

Note that in your case it would be Fragment.TAG, but I used ExampleFragment to clarify that Fragment.TAG is not part of the Android SDK.

To get a reference of your fragment in your activity, use the FragmentManager to find your fragment:

Fragment myFragment = getSupportFragmentManager().findFragmentByTag(ExampleFragment.TAG);

You can then make sure that myFragment is not null and cast it to FragmentCommunicator:

if (myFragment != null) {
    fragmentCommunicator = (FragmentCommunicator) myFragment;
}

Note that in your example fragmentCommunicator = (FragmentCommunicator) getApplication(); is invalid because it is your fragment that is implementing the interface, not your application.

Passing data From Activity to Fragment using interface

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