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Android App NullPointer Exception Help

harleyquin
harleyquin Member Posts: 2 Green Ribbon
edited Jan 27, 2022 5:40AM in Java Programming

Code for my android app it is a app that demonstrates how to communicate with multiple fragments in one activity. But the textview in the text fragment is not being updated after an item of the listview is selected. The textview should update when an item in the listview is selected but it is crashing due to a null pointer exception. I am learning from notes that are are from 2016 and some things are depreciated. I think it is the listener.OnFragmentInteraction it says listener points to null.

 fragment_text.xml
    <?xml version="1.0" encoding="utf-8"?>
    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/TextFragment_layout1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".TextFragment">
    
    
        <TextView
            android:id="@+id/textView1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="16dp"
            android:text="@string/welcome" />
    
    </FrameLayout>
    
    TextFragment.java
    package com.example.tourguide;
    
    import android.content.res.Resources;
    import android.net.Uri;
    import android.os.Bundle;
    
    import androidx.fragment.app.Fragment;
    
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;
    import android.widget.ListView;
    import android.widget.TextView;
    
    /**
     * A simple {@link Fragment} subclass.
     * Use the {@link TextFragment#newInstance} factory method to
     * create an instance of this fragment.
     */
    public class TextFragment extends Fragment
    {
        TextView textView;
    
    
        // TODO: Rename parameter arguments, choose names that match
        // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
        private static final String ARG_PARAM1 = "param1";
        private static final String ARG_PARAM2 = "param2";
    
        // TODO: Rename and change types of parameters
        private String mParam1;
        private String mParam2;
    
        public TextFragment() {
            // Required empty public constructor
        }
    
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment TextFragment.
         */
        // TODO: Rename and change types and number of parameters
        public static TextFragment newInstance(String param1, String param2) 
        {
            TextFragment fragment = new TextFragment();
            Bundle args = new Bundle();
            args.putString(ARG_PARAM1, param1);
            args.putString(ARG_PARAM2, param2);
            fragment.setArguments(args);
            return fragment;
        }
    
        @Override
        public void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            if (getArguments() != null)
            {
                mParam1 = getArguments().getString(ARG_PARAM1);
                mParam2 = getArguments().getString(ARG_PARAM2);
            }
    
        }
    
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup 
        container,
                                 Bundle savedInstanceState)
        {
            View view = inflater.inflate(R.layout.fragment_text, container, 
        false);
            textView = view.findViewById(R.id.textView1);
            return view;
        }
    
        public void updateTextView(int index)
        {
            if(index==0)
            {
                
        textView.setText(getResources().getString(R.string.set_Richmond));
            }
            else if(index==1)
            {
                
        textView.setText(getResources().getString(R.string.set_Vancouver));
            }
            else if(index==2)
            {
                
        textView.setText(getResources().getString(R.string.set_Toronto));
            }
            else if(index==3)
            {
                
        textView.setText(getResources().getString(R.string.set_New_West));
            }
            else if(index==4)
            {
                
        textView.setText(getResources().getString(R.string.set_Montreal));
            }
            else if(index==5)
            {
                
        textView.setText(getResources().getString(R.string.set_Aldergrove));
            }
        }
    
            public interface OnFragmentInteractionListener
        {
            public void onFragmentInteraction(int index);
        }
    }
    
    fragment_list.xml
    
    <?xml version="1.0" encoding="utf-8"?>
    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/ListFragment_layout1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".ListFragment">
    
        <ListView
            android:id="@+id/listView1"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:dividerHeight="32dp" />
    
    </FrameLayout>
    
    package com.example.tourguide;
    
    import android.content.res.Resources;
    import android.net.Uri;
    import android.os.Bundle;
    
    import androidx.fragment.app.Fragment;
    
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;
    import android.widget.AdapterView;
    
    import android.widget.ListView;
    
    /**
     * A simple {@link Fragment} subclass.
     * Use the {@link ListFragment#newInstance} factory method to
     * create an instance of this fragment.
     */
    public class ListFragment extends Fragment implements 
    AdapterView.OnItemClickListener
    {
        ListView listView;
        String[] array;
        String listStr;
        private OnFragmentInteractionListener listener;
    
    
    
        // TODO: Rename parameter arguments, choose names that match
        // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
        private static final String ARG_PARAM1 = "param1";
        private static final String ARG_PARAM2 = "param2";
    
        // TODO: Rename and change types of parameters
        private String mParam1;
        private String mParam2;
    
        public ListFragment() {
            // Required empty public constructor
        }
    
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment ListFragment.
         */
        // TODO: Rename and change types and number of parameters
        public static ListFragment newInstance(String param1, String param2) 
        {
            ListFragment fragment = new ListFragment();
            Bundle args = new Bundle();
            args.putString(ARG_PARAM1, param1);
            args.putString(ARG_PARAM2, param2);
            fragment.setArguments(args);
            return fragment;
        }
    
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            if (getArguments() != null)
            {
                mParam1 = getArguments().getString(ARG_PARAM1);
                mParam2 = getArguments().getString(ARG_PARAM2);
            }
        }
    
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup 
        container, Bundle savedInstanceState)
        {
            View view = inflater.inflate(R.layout.fragment_list, container, 
            false);
            listView = view.findViewById(R.id.listView1);
            array = 
            getResources().getStringArray(R.array.string_array_cities);
            ArrayAdapter<String> adapter = new ArrayAdapter<String> 
            (getActivity(), android.R.layout.simple_list_item_1, array);
            listView.setAdapter(adapter);
            listView.setOnItemClickListener(this);
            return view;
        }
    
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int 
        index, long id)
        {
            if(listener != null)
            {
                listener.onFragmentInteraction(index); //pass index of array
            }
        }
    
        public interface OnFragmentInteractionListener
        {
            public void onFragmentInteraction(int index);
        }
    }
    
    activity_main.xml
    
    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout 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:id="@+id/LinearLayout_1"
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">
    
        <androidx.fragment.app.FragmentContainerView
            android:id="@+id/fragmentContainerView1_list"
            android:name="com.example.tourguide.ListFragment"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1"
            tools:layout="@layout/fragment_list" />
    
        <androidx.fragment.app.FragmentContainerView
            android:id="@+id/fragmentContainerView2_text"
            android:name="com.example.tourguide.TextFragment"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1"
            tools:layout="@layout/fragment_text" />
    </LinearLayout>
    
    package com.example.tourguide;
    
    import androidx.appcompat.app.AppCompatActivity;
    import androidx.fragment.app.FragmentManager;
    
    import android.app.Fragment;
    import android.net.Uri;
    import android.os.Bundle;
    
    public class MainActivity extends AppCompatActivity implements 
    TextFragment.OnFragmentInteractionListener, 
    ListFragment.OnFragmentInteractionListener
    {
    
        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
        }
    
    
        @Override
        public void onFragmentInteraction(int index)
        {
            FragmentManager manager = getSupportFragmentManager();
            TextFragment textFragment = 
   (TextFragment)manager.findFragmentById(R.id.fragmentContainerView2_text);
            textFragment.updateTextView(index);
        }
    
    }
    
        strings.xml
    
        <resources>
        <string name="app_name">Tour Guide</string>
        <string name="hello_blank_fragment">Hello blank fragment</string>
        <string name="text_box">default</string>
        <string name="welcome">Welcome to the Tour Guide App</string>
    
        <string name="set_Richmond">Richmond is a quite city with many nice 
        hidden scenic places. A small town named Steveston is found on the 
        south 
        west part
        of the city and is well known for having good seafood and nice 
        places to visit like Garry Point and the west and south dykes. 
        </string>
    
        <string name="set_Vancouver">Vancouver is one of Canadas biggest 
        cities and has a lot to offer like the malls and many towers, 
        beaches, 
        parks.</string>
    
        <string name="set_Toronto">Toronto is Canadas biggest city on the 
        east coast and home to the TSX and Maple Leafs.</string>
    
        <string name="set_New_West">New West is a city east of Vancouver but 
        close by and has nice parks and ice rinks like Moody Park and Queens 
        Park.
        Queens Park home of the New West Royals.</string>
      
        <string name="set_Montreal">Monteal is famous for their smoked meat 
        and they speak french.</string>
    
        <string name="set_Aldergrove">Aldergrove is a quite town and is east 
        of Langley not too far and is a nice place.</string>
    
        <string-array name="string_array_cities">
            <item>Richmond</item>
            <item>Vancouver</item>
            <item>Toronto</item>
            <item>New West</item>
            <item>Montreal</item>
            <item>Aldergrove</item>
        </string-array>
    
    
    </resources>


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