Btukfyl

So, i am doing this for learning purposes,

What exactly i want to do is :

Create two fragments,
First fragment has a button which when pressed replaces the fragment View on the main activity with the second fragment, second fragment just contains a textview saying "This is second fragment" but when i tried to do it,
the first fragment is loaded two times and on button pressed, first instance stays where as the second instance is changed to the second fragment. Can you guys tell me what am i doing wrong : (i am attaching the code as well the the screenshots)

MainActivity.java :

package com.femindharamshi.fragmenttrials;



import android.support.v4.app.FragmentTransaction;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.Toast;



public class MainActivity extends AppCompatActivity implements FirstFragment.OnFragmentInteractionListener {



    FragmentTransaction fragmentTransaction;



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);



        fragmentTransaction = getSupportFragmentManager().beginTransaction();

        FirstFragment newFrament = new FirstFragment();

        fragmentTransaction.add(R.id.fragmentView, newFrament);

        fragmentTransaction.commit();



    }



    @Override

    public void onFragmentInteraction() {

        Toast.makeText(this, "Button in fragment pressed!", Toast.LENGTH_SHORT).show();

        fragmentTransaction = getSupportFragmentManager().beginTransaction();

        SecondFragment newFragment = new SecondFragment();

        fragmentTransaction.replace(R.id.fragmentView, newFragment);

        fragmentTransaction.commit();

    }

}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context=".MainActivity">



    <fragment

        android:id="@+id/fragmentView"

        android:name="com.femindharamshi.fragmenttrials.FirstFragment"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:layout_alignParentStart="true"

        android:layout_alignParentTop="true"/>

</RelativeLayout>

FirstFragment.java

package com.femindharamshi.fragmenttrials;



import android.content.Context;

import android.net.Uri;

import android.os.Bundle;

import android.support.v4.app.Fragment;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.Button;



public class FirstFragment extends Fragment {



    private OnFragmentInteractionListener mListener;



    Button button;



    public FirstFragment() {

        // Required empty public constructor

    }



    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment

        View view = inflater.inflate(R.layout.fragment_first, container, false);



        button = view.findViewById(R.id.button);



        button.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View view) {

                onButtonPressed();

            }

        });



        return view;

    }



    public void onButtonPressed() {

        if (mListener != null) {

            mListener.onFragmentInteraction();

        }

    }



    @Override

    public void onAttach(Context context) {

        super.onAttach(context);

        if (context instanceof OnFragmentInteractionListener) {

            mListener = (OnFragmentInteractionListener) context;

        } else {

            throw new RuntimeException(context.toString()

                    + " must implement OnFragmentInteractionListener");

        }

    }



    @Override

    public void onDetach() {

        super.onDetach();

        mListener = null;

    }

    public interface OnFragmentInteractionListener {

        void onFragmentInteraction();

    }

}

SecondFragment.java

package com.femindharamshi.fragmenttrials;



import android.os.Bundle;

import android.support.v4.app.Fragment;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;





public class SecondFragment extends Fragment {





    public SecondFragment() {

        // Required empty public constructor

    }





    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment

        return inflater.inflate(R.layout.fragment_second, container, false);

    }





    @Override

    public void onDetach() {

        super.onDetach();

    }

}

Problem : Also, without mentioning android:name="com.femindharamshi.fragmenttrials.FirstFragment" in the main activity, the app crashes. What if i don't want to load a fragment when the activity start, why do i have to mention this ? and even if i load secondFragment in this, is it okay ? even though in the name it says FirstFragment?

What if i don't want to assign the in the main activity with a fragment class before hand, and want to do it programmatically ?

Screenshots :