Develop Reference

Invoke Virtual Method on null object reference

I am trying to implement fragments for a project in Android Studio. The point of the project is to select a color from a spinner in one fragment then pass it to the parent activity and then pass it from the parent activity to the second fragment to change the background color of the second fragment. The problem I am having is my listener in the palette activity is set to null despite the fact I invoke it in the onAttach function.
This is my code for the Fragment that causes the app to crash
package edu.temple.palettecolorapp;
import android.content.Context;
import android.graphics.Color;
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.AdapterView;
import android.widget.Spinner;
/**
* A simple {#link Fragment} subclass.
* Activities that contain this fragment must implement the
* {#link PaletteFragment.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {#link PaletteFragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class PaletteFragment extends Fragment {
private String colorArr[];
private String translationArr[];
Context parent;
private final String mParam1 = "colors";
private final String mParam2 = "translation";
public OnFragmentInteractionListener mListener;
public PaletteFragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
*
* #return A new instance of fragment PaletteFragment.
*/
// TODO: Rename and change types and number of parameters
public static PaletteFragment newInstance(String colors[], String translation[]) {
PaletteFragment fragment = new PaletteFragment();
Bundle args = new Bundle();
args.putStringArray("colors", colors);
args.putStringArray("translation", translation);
fragment.setArguments(args);
return fragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
this.colorArr = getArguments().getStringArray(mParam1);
this.translationArr = getArguments().getStringArray(mParam2);
}
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
this.parent = context;
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) parent;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
// this.parent = context;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_palette, container, false);
Spinner spinner = v.findViewById(R.id.spinner);
PaletteAdapter pa = new PaletteAdapter(parent,colorArr,translationArr);
spinner.setAdapter(pa);
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
#Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String c = colorArr[position];
mListener.onColorSelection(c);
}
#Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
return v;
}
#Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
public void onColorSelection(String color);
}
}
This is in the main activity
package edu.temple.palettecolorapp;
import android.content.Intent;
import android.content.res.Resources;
import android.net.Uri;
import android.support.constraint.ConstraintLayout;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.AdapterView;
import android.widget.Spinner;
import android.content.Context;
import android.graphics.Color;
import android.view.View;
public class PaletteActivity extends AppCompatActivity implements PaletteFragment.OnFragmentInteractionListener {
PaletteFragment master;
ColorFragment subject;
FragmentTransaction ft;
private final String colors[] = {"blue", "green", "purple", "red", "gray", "cyan", "magenta", "yellow", "lime"};
private boolean isSelected = false;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Context context = getApplicationContext();
Resources res = context.getResources();
String title = res.getString(R.string.palette_title);
setTitle(title);
setContentView(R.layout.activity_palette);
String translation[] = res.getStringArray(R.array.colors);
PaletteFragment master = PaletteFragment.newInstance(colors,translation);
ColorFragment subject = ColorFragment.newInstance("magenta");
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.add(R.id.fragment1,master);
ft.replace(R.id.fragment2,subject);
ft.addToBackStack(null);
ft.commit();
}
#Override
public void onColorSelection(String color) {
subject.updateBackgroundColor(color);
}
}
I am having trouble in this portion of the fragment in the 'onCreateView' method
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_palette, container, false);
Spinner spinner = v.findViewById(R.id.spinner);
PaletteAdapter pa = new PaletteAdapter(parent,colorArr,translationArr);
spinner.setAdapter(pa);
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
#Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String c = colorArr[position];
mListener.onColorSelection(c);
}
#Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
return v;
}
The 'mListener.onColorSelection' call causes the error and this is what the output is
E/AndroidRuntime: FATAL EXCEPTION: main
Process: edu.temple.palettecolorapp, PID: 14867
java.lang.NullPointerException: Attempt to invoke virtual method 'void edu.temple.palettecolorapp.ColorFragment.updateBackgroundColor(java.lang.String)' on a null object reference
at edu.temple.palettecolorapp.PaletteActivity.onColorSelection(PaletteActivity.java:45)
at edu.temple.palettecolorapp.PaletteFragment$1.onItemSelected(PaletteFragment.java:87)
at android.widget.AdapterView.fireOnSelected(AdapterView.java:944)
at android.widget.AdapterView.dispatchOnItemSelected(AdapterView.java:933)
at android.widget.AdapterView.access$300(AdapterView.java:53)
at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:898)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Edit2: added ColorFragment 'updateBackgroundColor' method
import android.content.Context;
import android.graphics.Color;
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.TextView;
/**
* A simple {#link Fragment} subclass.
* Activities that contain this fragment must implement the
* to handle interaction events.
* Use the {#link ColorFragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class ColorFragment extends Fragment {
private View v;
TextView t;
String color;
private final String KEY = "color";
public ColorFragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters
* #return A new instance of fragment ColorFragment.
*/
// TODO: Rename and change types and number of parameters
public static ColorFragment newInstance() {
ColorFragment fragment = new ColorFragment();
return fragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
this.color = getArguments().getString(KEY);
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
v = inflater.inflate(R.layout.fragment_color, container, false);
t = v.findViewById(R.id.textView);
t.setBackgroundColor(Color.BLACK);
return v;
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
}
#Override
public void onDetach() {
super.onDetach();
}
public void updateBackgroundColor(String c){ // causing problems
t.setBackgroundColor(Color.parseColor(c));
}
}

Apparently ColorFragment subject in PaletteActivity is null when calling #onColorSelection().
Please check the assignment of value for the variable and make sure it is not null.
#Override
public void onColorSelection(String color) {
subject.updateBackgroundColor(color);
}
EDIT:
change the line:
ColorFragment subject = ColorFragment.newInstance("magenta");
TO:
subject = ColorFragment.newInstance("magenta");

VideoView starts playing in a wrong fragment using viewpager

Problem: I have a viewPager with 3 fragments, the first one has a videoView. When I change to the second fragment, the video stops and when I change to the third, the same. But when I change from the third fragment to the second one, the video starts playing in the background.
I want the video to play only in the first fragment. How can i solve this problem? Thanks
Here is my code:
Activity Adapter:
import android.net.Uri;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class ActivitySwipe extends AppCompatActivity implements
HomeFragment.OnFragmentInteractionListener ,
CamaraFragment.OnFragmentInteractionListener
, SearchFragment.OnFragmentInteractionListener{
/**
* The {#link android.support.v4.view.PagerAdapter} that will provide
* fragments for each of the sections. We use a
* {#link FragmentPagerAdapter} derivative, which will keep every
* loaded fragment in memory. If this becomes too memory intensive, it
* may be best to switch to a
* {#link android.support.v4.app.FragmentStatePagerAdapter}.
*/
private SectionsPagerAdapter mSectionsPagerAdapter;
/**
* The {#link ViewPager} that will host the section contents.
*/
private ViewPager mViewPager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_swipe);
/* Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);*/
// Create the adapter that will return a fragment for each of the three
// primary sections of the activity.
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
final HomeFragment homeFragment = new HomeFragment();
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
/* FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});*/
mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
public void onPageScrollStateChanged(int state) {}
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
public void onPageSelected(int position) {
// Check if this is the page you want.
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_activity_swipe, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
#Override
public void onFragmentInteraction(Uri uri) {
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
public PlaceholderFragment() {
}
/**
* Returns a new instance of this fragment for the given section
* number.
*/
public static Fragment newInstance(int sectionNumber) {
Fragment fragment = null;
switch (sectionNumber){
case 1 : fragment=new HomeFragment();
break;
case 2 : fragment=new CamaraFragment();
break;
case 3 : fragment=new SearchFragment();
break;
}
return fragment;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_activity_swipe, container, false);
TextView textView = (TextView) rootView.findViewById(R.id.section_label);
textView.setText(getString(R.string.section_format, getArguments().getInt(ARG_SECTION_NUMBER)));
return rootView;
}
}
/**
* A {#link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a PlaceholderFragment (defined as a static inner class below).
return PlaceholderFragment.newInstance(position + 1);
}
#Override
public int getCount() {
// Show 3 total pages.
return 3;
}
}
}
Here is my 1st fragment:
import android.content.Context;
import android.media.MediaPlayer;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.VideoView;
/**
* A simple {#link Fragment} subclass.
* Activities that contain this fragment must implement the
* {#link HomeFragment.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {#link HomeFragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class HomeFragment extends Fragment{
// 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";
VideoView videoview;
MediaPlayer mediap;
int position;
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private OnFragmentInteractionListener mListener;
public HomeFragment() {
// 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 HomeFragment.
*/
// TODO: Rename and change types and number of parameters
public static HomeFragment newInstance(String param1, String param2) {
HomeFragment fragment = new HomeFragment();
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);
setUserVisibleHint(false);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v= inflater.inflate(R.layout.fragment_home, container, false);
videoview = (VideoView) v.findViewById(R.id.video1);
videoview.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
#Override
public void onPrepared( MediaPlayer mp) {
mp.setLooping(true);
mediap=mp;
}
});
Uri uri = Uri.parse("android.resource://" + getActivity().getPackageName() + "/" + R.raw.vid5);
videoview.setVideoURI(uri);
videoview.requestFocus();
videoview.start();
return v;
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser) {
resume();
}
else {
pause();
}
}
#Override
public void setMenuVisibility(final boolean visible) {
super.setMenuVisibility(visible);
if (visible&&isResumed()) {
resume();
}else{
pause();
}
}
#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");
}
}
public void pause(){
//NOT videoview.pause(); Needn't save Stop position
if (mediap != null){
mediap.pause();
}
}
public void resume(){
//NOT videoview.resume();
if (mediap != null){
mediap.start(); //Video will begin where it stopped
}
}
#Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
And my 2nd fragment:
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;
/**
* A simple {#link Fragment} subclass.
* Activities that contain this fragment must implement the
* {#link CamaraFragment.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {#link CamaraFragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class CamaraFragment extends Fragment {
// 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;
private OnFragmentInteractionListener mListener;
public CamaraFragment() {
// 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 CamaraFragment.
*/
// TODO: Rename and change types and number of parameters
public static CamaraFragment newInstance(String param1, String param2) {
CamaraFragment fragment = new CamaraFragment();
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) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_camara, container, false);
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
#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;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}

When you use an FragmentPagerAdapter, it pre-loads your fragments to left and right of your fragment in focus. So when you scroll from position 0 to 1 to 2, the fragment in position 0 is removed. When you then scroll back to position 1, the fragment in position 0 is re-loaded, which triggers creating the view. If you look at your HomeFragment, you trigger playing video when in OnCreateView().
To resolve this, you need to change how you trigger playing the video from when the Fragment is created to instead be activated when it scrolls into view. You are already halfway there with your empty OnPageChangeListener. You should check the position in onPageSelected() and start the video there instead of in the Fragment's OnCreateView

You have to override setUserVisibleHint method in a fragment where you play video.
public void setUserVisibleHint
#Override
public void setUserVisibleHint(boolean isVisibleToUser)
{
super.setUserVisibleHint(isVisibleToUser);
if (this.isVisible())
{
if (!isVisibleToUser)
{
//pause or stop video
} else {
//play your video
}
}
}

How to create fragment interaction?

These are the imports I have for the fragment class.
import android.os.Bundle;
import android.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
Class being initialized
public class FragmentDemo extends Fragment {
Public constructor is empty and must stay that way
public FragmentDemo() {
}
It must be attached to an activity, the interface depends on said activity
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
Inflating layout for fragment
View result = inflater.inflate(R.layout.fragment_fragment_demo, container, false);
TextView textView = (TextView)result.findViewById(R.id.textView2);
Button button = (Button)result.findViewById(R.id.button2);
textView.setText("HEY, THIS IS A TEST!");
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Log.e("FRAGMENT", "BUTTON IS WORKING!");
// why no toast?
}
});
return result;
}
}

You must create two classes to make it more clear, one for the interaction of fragments, and a main class.
The first one should look like this:
import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import android.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import org.w3c.dom.Text;
/**
* A simple {#link Fragment} subclass.
* Activities that contain this fragment must implement the
* {#link InteractionFragment.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {#link InteractionFragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class InteractionFragment extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_NAME = "name";
private static final String ARG_LAST_NAME = "lastName";
// TODO: Rename and change types of parameters
private String name;
private String lastName;
private OnFragmentInteractionListener mListener;
public InteractionFragment() {
// 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 InteractionFragment.
*/
// TODO: Rename and change types and number of parameters
// Factory method
public static InteractionFragment newInstance(String param1, String param2) {
InteractionFragment fragment = new InteractionFragment();
Bundle args = new Bundle();
args.putString(ARG_NAME, param1);
args.putString(ARG_LAST_NAME, param2);
fragment.setArguments(args);
return fragment;
}
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
name = getArguments().getString(ARG_NAME);
lastName = getArguments().getString(ARG_LAST_NAME);
}
}
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v = inflater.inflate(R.layout.fragment_interaction, container, false);
TextView nameText = (TextView)v.findViewById(R.id.name);
TextView lastNameText = (TextView)v.findViewById(R.id.last_name);
nameText.setText(name);
lastNameText.setText(lastName);
Button button = (Button)v.findViewById(R.id.button3);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
mListener.somethingHappened("THE BUTTON WAS PRESSED, HOW EXCITING!");
}
});
return v;
}
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
public void onDetach() {
super.onDetach();
mListener = null;
}
public void printALog(){
Log.wtf("PRINTING", "ITS WORKING!");
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
void somethingHappened(String message);
}
}
While the second one should look like this:
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.TransactionTooLargeException;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity implements InteractionFragment.OnFragmentInteractionListener {
InteractionFragment fragment;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
private void addFragment(Fragment f){
// add a fragment through code
// fragment manager - the guy in charge of any fragment related logic
FragmentManager manager = getFragmentManager();
// transactions
FragmentTransaction transaction = manager.beginTransaction();
// actually do the thing
//fragment = InteractionFragment.newInstance("Juan","Perez");
// 3rd parameter - fragment
transaction.add(R.id.container, f, "dude");
transaction.commit();
}
#Override
public void somethingHappened(String message) {
Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
}
public void doSomethingOnFragment(View v){
fragment.printALog();
}
public void swapFragments(View v){
FragmentManager manager = getFragmentManager();
Fragment f = manager.findFragmentByTag("dude");
if(f != null){
Toast.makeText(this, "FRAGMENT BEING REMOVED", Toast.LENGTH_SHORT).show();
FragmentTransaction transaction = manager.beginTransaction();
transaction.remove(f);
transaction.commit();
} else {
Toast.makeText(this, "NO FRAGMENT TO REMOVE", Toast.LENGTH_SHORT).show();
}
}
public void addFragment1(View v){
fragment = InteractionFragment.newInstance("Juan","Perez");
addFragment(fragment);
}
public void addFragment2(View v){
FragmentDemo fd = new FragmentDemo();
addFragment(fd);
}
}

I'm not sure to understand what is your question exactly, so I will assume first that your problem is related to your "Why no toast?" comment.
The thing is you are using the log function, this prints in logcat console, not through toasts.
If you want to display a toast, use
Toast.makeText(context, text, durationInMs).show();
More info here

I'm not sure to understand what is your question exactly, so I will assume first that your problem is related to your "Why no toast?" comment.
The thing is you are using the log function, this prints in logcat console, not through toasts.
If you want to display a toast, use
Toast.makeText(context, text, durationInMs).show();
And because you are in a Fragment the Context used is the activity which has this fragment so to get context we use getActivity(). Hence the Toast will be:
Toast.makeText(getActivity(), text, Toast.LENGTH_SHORT).show();

Attempt to invoke virtual method results in a null pointer exception [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 7 years ago.
import android.app.Activity;
import android.media.MediaPlayer;
import android.media.MediaRecorder;
import android.os.Bundle;
import android.provider.MediaStore;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.ListAdapter;
import android.widget.TextView;
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import umd.frenchpronunciationapp.dummy.DummyContent;
/**
* A fragment representing a list of Items.
* <p/>
* Large screen devices (such as tablets) are supported by replacing the ListView
* with a GridView.
* <p/>
* Activities containing this fragment MUST implement the {#link OnFragmentInteractionListener}
* interface.
*/
public class FragmentList1 extends Fragment implements AbsListView.OnItemClickListener{
// 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;
TextView text1;
private Button button1 = (Button) getView().findViewById(R.id.male);
private Button button2 = (Button) getView().findViewById(R.id.female);
ArrayList <String> phrases = new ArrayList<String> ();
private OnFragmentInteractionListener mListener;
/**
* The fragment's ListView/GridView.
*/
private AbsListView mListView;
/**
* The Adapter which will be used to populate the ListView/GridView with
* Views.
*/
private ListAdapter mAdapter;
// TODO: Rename and change types of parameters
public static FragmentList1 newInstance(String param1, String param2) {
FragmentList1 fragment = new FragmentList1();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
/**
* Mandatory empty constructor for the fragment manager to instantiate the
* fragment (e.g. upon screen orientation changes).
*/
public FragmentList1() {
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
// TODO: Change Adapter to display your content
mAdapter = new ArrayAdapter<DummyContent.DummyItem>(getActivity(),
android.R.layout.simple_list_item_1, android.R.id.text1, DummyContent.ITEMS);
addListenerOnButtonMale();
addListenerOnButtonFemale();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_item, container, false);
// Set the adapter
mListView = (AbsListView) view.findViewById(android.R.id.list);
((AdapterView<ListAdapter>) mListView).setAdapter(mAdapter);
// Set OnItemClickListener so we can be notified on item clicks
mListView.setOnItemClickListener(this);
return view;
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mListener = (OnFragmentInteractionListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnFragmentInteractionListener");
}
}
#Override
public void onDetach() {
super.onDetach();
mListener = null;
}
public void readInPhrases () throws IOException
{
String str;
InputStream myStream = getResources().openRawResource(R.raw.phrases);
BufferedReader reader = new BufferedReader(new InputStreamReader(myStream));
while ((str = reader.readLine()) != null)
{
phrases.add(str);
}
}
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id)
{
if (null != mListener) {
// Notify the active callbacks interface (the activity, if the
// fragment is attached to one) that an item has been selected.
mListener.onFragmentInteraction(DummyContent.ITEMS.get(position).id);
}
text1 = (TextView) getView ().findViewById (R.id.phrase);
try {
readInPhrases();
}
catch (IOException ex)
{
// catches overidden error ioexecption
}
MediaPlayer mp1 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g1));
MediaPlayer mp2 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g2));
MediaPlayer mp3 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g3));
MediaPlayer mp4 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g4));
MediaPlayer mp5 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g5));
MediaPlayer mp6 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g6));
MediaPlayer mp7 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g7));
MediaPlayer mp8 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g8));
MediaPlayer mp9 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g9));
MediaPlayer mp10 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g10));
MediaPlayer mp11 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g11));
MediaPlayer mp12 = MediaPlayer.create (getActivity().getApplicationContext(), (R.raw.g12));
switch (position){
default:
case 0:
text1.setText (phrases.get(0));
// to incorperate male voice, do this and have male and female buttons
// and a variable that holds true or false if button was pressed
//if (male == true)
mp1.start();
//else
//mp... .start ();
break;
case 1:
text1.setText (phrases.get (1));
mp2.start ();
break;
case 2:
text1.setText (phrases.get (2));
mp3.start ();
break;
case 3:
text1.setText (phrases.get (3));
mp4.start ();
break;
case 4:
text1.setText (phrases.get (4));
mp5.start ();
break;
case 5:
text1.setText (phrases.get (5));
mp6.start ();
break;
case 6:
text1.setText (phrases.get (6));
mp7.start ();
break;
case 7:
text1.setText (phrases.get (7));
mp8.start ();
break;
case 8:
text1.setText (phrases.get (8));
mp9.start ();
break;
case 9:
text1.setText (phrases.get (9));
mp10.start ();
break;
case 10:
text1.setText (phrases.get (10));
mp11.start ();
break;
case 11:
text1.setText (phrases.get (11));
mp12.start ();
break;
}
}
public void addListenerOnButtonMale ()
{
//male.setBackgroundResource((R.drawable.malelogo));
button1.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// Perform action on click
}
});
}
public void addListenerOnButtonFemale ()
{
//female.setBackgroundResource((R.drawable.femalelogo));
button2.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
MediaPlayer mp1 = MediaPlayer.create(getActivity().getApplicationContext(), (R.raw.g1));
mp1.start();
}
});
}
/**
* The default content for this Fragment has a TextView that is shown when
* the list is empty. If you would like to change the text, call this method
* to supply the text it should use.
*/
public void setEmptyText(CharSequence emptyText) {
View emptyView = mListView.getEmptyView();
if (emptyView instanceof TextView) {
((TextView) emptyView).setText(emptyText);
}
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p/>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
public void onFragmentInteraction(String id);
}
}
The addition of the addListenerOnButtonMale(); in the onCreate() method causes my app to crash. I looked around for answers that would help with the NullPointerException but they all stated that i needed to declare the button before the method was called and this still doesn't help with anything.

Your onCreate():
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
// TODO: Change Adapter to display your content
mAdapter = new ArrayAdapter<DummyContent.DummyItem>(getActivity(),
android.R.layout.simple_list_item_1, android.R.id.text1, DummyContent.ITEMS);
addListenerOnButtonMale();
addListenerOnButtonFemale();
}
Your addListenerOnButtonMale():
public void addListenerOnButtonMale ()
{
//male.setBackgroundResource((R.drawable.malelogo));
button1.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// Perform action on click
}
});
}
Check your onCreate()... you have not initialised the button1.. Thats why you are getting NullPoitnerException.
Remove the addListenerOnButtonMale(); and addListenerOnButtonFemale(); from your onCreate();
Modify your onCreateView() as below:
First initialise by finding the reference and then, call your methods:
public void onCreateView(){
View view = inflater.inflate(R.layout.fragment_item, container, false);
// Set the adapter
mListView = (AbsListView) view.findViewById(android.R.id.list);
((AdapterView<ListAdapter>) mListView).setAdapter(mAdapter);
// Set OnItemClickListener so we can be notified on item clicks
mListView.setOnItemClickListener(this);
button1 = (Button) view.findViewById(R.id.*button1*);// place id of your button1.
button2 = (Button) view.findViewById(R.id.*button2*);// place id of your button2.
addListenerOnButtonMale();
addListenerOnButtonFemale();
return view;
}

ListView not being destroyed/deflated on orientation change

I've got this problem where when I change the orientation of my device, for some reason the on-screen representation of the ListView associated with my ListFragment is retained, and a new ListView is inflated beneath it. To give you some context, I am creating a very simple app whose purpose is to test some DAO objects I created. I would have preferred to post some screenshots depicting the behavior my app is experiencing, but unfortunately, my reputation is too low at the moment.
The best I could describe it would be that when I change the orientation of the device from portrait to landscape (and vice versa), it inflates a whole new ListView without deflating the previous one. I have been looking into this for a couple of days now, and quite honestly, I am stumped. Any help you guys could offer would be greatly appreciated.
Here is the code for the ListFragment:
package edu.uark.csce.mobile.healthyshopper;
import android.app.ListFragment;
import android.app.LoaderManager.LoaderCallbacks;
import android.content.CursorLoader;
import android.content.Loader;
import android.content.SharedPreferences;
import android.database.Cursor;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
/**
* A fragment representing a list of Items.
* <p />
* <p />
* Activities containing this fragment MUST implement the {#link Callbacks}
* interface.
*/
public class ViewFragment extends ListFragment implements
LoaderCallbacks<Cursor> {
// Class Fields:
private static final String TAG = "healthyshopper.ViewFragment";
private static final int MAIN_DB_LOADER = 0;
// In the final application, any query to the main database needs to return
// at least these fields:
private final String[] NECESSARY_COLUMNS = { DAOContentProvider.FOOD_DES,
DAOContentProvider.FOOD_CALORIES, DAOContentProvider.FOOD_FAT,
DAOContentProvider.FOOD_CARBS, DAOContentProvider.FOOD_PROTEIN };
private final String FROM[] = {DAOContentProvider.FOOD_GROUP, DAOContentProvider.FOOD_DES,
DAOContentProvider.FOOD_MANUFAC, DAOContentProvider.FOOD_PROTEIN,
DAOContentProvider.FOOD_FAT, DAOContentProvider.FOOD_CARBS,
DAOContentProvider.FOOD_CALORIES, DAOContentProvider.FOOD_SERV_SIZE};
private final int TO[] = {R.id.fd_group, R.id.shrt_desc,
R.id.manufac, R.id.protein,
R.id.fat, R.id.carb,
R.id.cal, R.id.amt};
private int threadMode;
private int queryType;
private int foodGroupId;
private CursorLoader loader;
private SimpleCursorAdapter listAdapter;
// Preference Option Constants:
private int UI_THREAD = 0;
private int BRANCHED_THREAD = 1;
private int ALL_ROWS = 0;
private int SPECIFIC_FD_GROUP = 1;
private int LIMITED_ROWS = 2;
private OnFragmentInteractionListener mListener;
/**
* Mandatory empty constructor for the fragment manager to instantiate the
* fragment (e.g. upon screen orientation changes).
*/
public ViewFragment() {
}
/***************************************
* Life cycle callbacks:
*/
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.e(TAG, "in onCreate()");
setRetainInstance(true);
}
#Override
public void onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
if(savedInstanceState == null){
listAdapter = new SimpleCursorAdapter(getActivity(), R.layout.list_node, null, FROM, TO, 0);
setListAdapter(listAdapter);
}
}
#Override
public void onStart(){
super.onStart();
}
#Override
public void onResume(){
super.onResume();
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity()
.getApplicationContext());
Log.d(TAG, preferences.getString("THREADING_MODE", "BLANK"));
//Load testing preferences:
threadMode = Integer.valueOf(preferences.getString("THREADING_MODE","0"));
queryType = Integer.valueOf(preferences.getString("QUERY_TYPE", "0"));
foodGroupId = Integer.valueOf(preferences.getString("FOOD_GROUP", "0")); // Default
if (threadMode == BRANCHED_THREAD) {
loader = (CursorLoader) getLoaderManager().initLoader(
MAIN_DB_LOADER, null, this);
} else {
String[] projection = null;
String selection = null;
if (queryType == SPECIFIC_FD_GROUP) {
Log.d(TAG, "Query Type: " + (getResources().getStringArray(R.array.query_type_select))[queryType]);
selection = DAOContentProvider.FOOD_GROUP + " = " + foodGroupId;
} else if (queryType == LIMITED_ROWS) {
projection = NECESSARY_COLUMNS;
}
/*This is for testing only. Ordinarily, you should NEVER perform Db operations on the UI thread.*/
listAdapter.swapCursor(getActivity().getContentResolver().query(
DAOContentProvider.CONTENT_URI, projection, selection, null, null));
}
}
#Override
public void onPause(){
super.onPause();
}
#Override
public void onStop(){
super.onStop();
}
#Override
public void onDestroyView(){
super.onDestroyView();
Log.e(TAG, "in onDestroyView()");
setListAdapter(null);
listAdapter.swapCursor(null);
listAdapter = null;
}
#Override
public void onDestroy(){
super.onDestroy();
}
#Override
public void onDetach(){
super.onDetach();
}
#Override
public void onListItemClick(ListView l, View v, int position, long id) {
super.onListItemClick(l, v, position, id);
if (null != mListener) {
}
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated to
* the activity and potentially other fragments contained in that activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
public void onFragmentInteraction(String id);
}
/**
* LoaderManager Callbacks;
*/
#Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
switch (id) {
case MAIN_DB_LOADER:
String[] projection = null;
String selection = null;
if (queryType == SPECIFIC_FD_GROUP) {
Log.d(TAG,
"Query Type: "
+ (getResources()
.getStringArray(R.array.query_type_select))[queryType]);
selection = DAOContentProvider.FOOD_GROUP + " = " + foodGroupId;
} else if (queryType == LIMITED_ROWS) {
projection = NECESSARY_COLUMNS;
}
return new CursorLoader(getActivity(),
DAOContentProvider.CONTENT_URI, projection, selection,
null, null);
default:
return null;
}
}
#Override
public void onLoadFinished(Loader<Cursor> arg0, Cursor arg1) {
listAdapter.swapCursor(arg1);
listAdapter.notifyDataSetChanged();
}
#Override
public void onLoaderReset(Loader<Cursor> arg0) {
listAdapter.swapCursor(null);
listAdapter.notifyDataSetChanged();
}
}
And here is the code for its associated Activity:
package edu.uark.csce.mobile.healthyshopper;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
public class TestingActivity extends Activity implements ViewFragment.OnFragmentInteractionListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_testing);
ViewFragment list = new ViewFragment();
getFragmentManager().beginTransaction().add(R.id.test_layout, list).commit();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.testing, menu);
return true;
}
#Override
public void onFragmentInteraction(String id) {
// TODO Auto-generated method stub
}
}

You're using setRetainInstance(true); in your fragment. This makes the fragment to be retained and reused when the activity is re-created.
You can read more detailed description in this question: Further understanding setRetainInstance(true)