listener

AbcActivity.java

package com.bullhead.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Toast;

public class AbcActivity extends AppCompatActivity implements FragmentOne.Listener{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_abc);
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.container,new FragmentOne())
                .commit();
    }

    @Override
    public void onButtonClick() {
        Toast.makeText(this,"Button clicked.",Toast.LENGTH_LONG).show();
    }
}

FragmentOne.java

package com.bullhead.myapplication;

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import butterknife.ButterKnife;
import butterknife.OnClick;

public class FragmentOne extends Fragment {
    public interface Listener{
        void onButtonClick();
    }
    private Listener listener;

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        listener= (Listener) context;
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_one, container, false);
        ButterKnife.bind(this,view);
        return view;
    }

    @OnClick({R.id.btnClick})
    public void onClick(View view){
        listener.onButtonClick();
    }
}

FragmentTwo.java

package com.bullhead.myapplication;

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import butterknife.BindView;
import butterknife.ButterKnife;

public class FragmentTwo extends Fragment {
    @BindView(R.id.tvClick)
    TextView tvClick;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fargment_two, container, false);
        ButterKnife.bind(this,view);
        return view;
    }

    public void buttonClicked() {
        tvClick.setText("Button clicked.");
    }
}

MainActivity.java

package com.bullhead.myapplication;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity implements FragmentOne.Listener{
    private FragmentOne fragmentOne;
    private FragmentTwo fragmentTwo;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        fragmentOne=new FragmentOne();
        fragmentTwo=new FragmentTwo();
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.frameOne,fragmentOne)
                .commit();
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.frameTwo,fragmentTwo)
                .commit();
    }


    @Override
    public void onButtonClick() {
        Intent intent=new Intent(this,AbcActivity.class);
        startActivity(intent);
    }
}