Access a method of a Fragment from the ViewPager Activity

Access a method of a Fragment from the ViewPager Activity - android

I have a Fragment with a method setName() that changes an EditText text, by means of the setText function.
What is the best way to call that method from the activity that hosts that fragment by means of a ViewPager?
In other words, how can I access a Fragment's methods (which change that fragment's layout, for example) from the Activity that hosts that fragment by means of a ViewPager?
I am asking this because I have tried several ways, but always with errors.

Best way to do this, just call
CallingFragmentName fragment = (CallingFragmentName) viewPager
.getAdapter()
.instantiateItem(viewPager, viewPager.getCurrentItem());
It will re-instantiate your calling Fragment, so that it will not throw null pointer exception.

I know this is a little late, but I ran into the same problem and maybe it will help others if you already solved it.
The first problem I found with ViewPager is that it is almost impossible to get a reference to a fragment. The fragments are created dynamically in getItem() and therefore you can't set an ID and they are automatically re-taged by the swicher, so you can't find it by tag either. There are some ways out there to do it, but they are all workarounds. (Update data in ListFragment as part of ViewPager)
The way I solved it was using essentially a double Callback. Fragment A has an interface implemented by the Main Activity, the Main Activity has a interface implemented by Fragment B. On e.g. a button clink in Fragment A the callback function in Main Activity is called, which than in turn calls the callback in Fragment B. Look at the code below. I hope I posted everything and it will help. btw, I have only tried this with a ViewPager, but I assume it would work with any sort of Fragment communication.
Main Avtivity java:
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
public class MainActivity extends FragmentActivity implements FragmentA.Caller {
SectionsPagerAdapter mSectionsPagerAdapter;
ViewPager mViewPager;
PassCallToB passOnToB = null;
FragmentManager myManager = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mSectionsPagerAdapter);
}
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
MyManager = fm;
}
#Override
public Fragment getItem(int position) {
Fragment fragment = null;
if(position == 0) {
fragment = new FragmentA();
} else if (position == 1) {
fragment = new FragmentB();
passOnToB = (PassCallToB)fragment;
}
return fragment;
}
#Override
public int getCount() {
return 2;
}
#Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Frag A";
case 1:
return "Frag B";
}
return null;
}
public void setCallback() {
List<Fragment> frags = myManager.getFragments();
for(Fragment fragment : frags) {
if(fragment instanceof FragmentB){
passOnToB = (PassCallToB)fragment;
}
}
}
}
public interface PassCallToB {
public void passItOn();
}
#Override
public void CallB() {
if(passOnToB instanceof Fragment)
passOnToB.passItOn();
else {
mSectionsPagerAdapter.setCallback();
passOnToB.passItOn();
}
}
}
Main Activity xml:
<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
<android.support.v4.view.PagerTitleStrip
android:id="#+id/pager_title_strip"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="top"
android:background="#33b5e5"
android:paddingBottom="4dp"
android:paddingTop="4dp"
android:textColor="#fff" />
</android.support.v4.view.ViewPager>
Fragment A java:
import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
public class FragmentA extends Fragment {
Button btnCallB = null;
Caller listener = null;
public FragmentA() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle inState) {
View rootView = inflater.inflate(R.layout.fragment_a, container, false);
btnCallB = (Button)rootView.findViewById(R.id.btnCallB);
btnCallB.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View view) {
listener.CallB();
}
});
return rootView;
}
public interface Caller {
public void CallB();
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
if (activity instanceof FragmentActivity) {
listener = (Caller) activity;
} else {
throw new ClassCastException(activity.toString() + " must implemenet listener");
}
}
#Override
public void onDetach() {
super.onDetach();
listener = null;
}
}
Fragment A xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:text="This is Fragment A" />
<Button
android:id="#+id/btnCallB"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="#+id/textView1"
android:text="Call Fragment B" />
</RelativeLayout>
Fragment B Java:
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.Toast;
public class FragmentB extends Fragment implements MainActivity.PassCallToB {
public FragmentB() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle inState) {
View rootView = inflater.inflate(R.layout.fragment_b, container, false);
return rootView;
}
#Override
public void passItOn() {
Toast.makeText(getActivity(), "Hello from B", Toast.LENGTH_SHORT).show();
}
}
Fragment B xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:text="This is Fragment B" />
</RelativeLayout>

You can access public methods within the fragments held by your ViewPager. You need to either (1) store a reference to the Fragment when you create it and add it to the list that will back your pager adapter or (2) you need to get a reference to the fragment from the pager adapter itself. For example:
Fragment fragmentA = null; //instance variable
fragmenA = new Fragment(); //whereever you instantiate your fragment
If your method is
public void setName(String args){
//do something
}
all you would do is call that method from the reference to the fragment held by your ViewPager
fragmentA.setName(args);
You pass whatever arguments you need just like calling a regular method. Note this ONLY works if you are calling a method within a fragment from its containing ViewPager or FragmentActivity. If you want to do the reverse, fragment to activity, you need to use an inerface.

Fragment
private static FragmentName instance;
public static synchronized FragmentName getInstance()
{
return instance;
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
instance=this;
....
}
public void methodName()
{...}
Activity
FragmentName.getInstance().methodName();

Related

Android: getArguments() in Fragment returns null, even though I setArguments() inside newInstance()

I want to pass arguments to my PopularMoviesFragment using newInstance() method. I have MainActivity where inside onOptionsItemSelected() I create a fragment using PopularMoviesFragment.newInstance("popularity.desc") and then make a transaction.
Inside the PopularMoviesFragment: I set arguments newInstance(String sortBy) using setArguments(), but when I want to retrieve them inside onCreate(), getArguments() returns null.
Here is the code, PopularMoviesFragment:
public class PopularMoviesFragment extends Fragment {
public static PopularMoviesFragment newInstance(String sortBy) {
PopularMoviesFragment fragment = new PopularMoviesFragment();
Bundle args = new Bundle();
args.putString("sortBy", sortBy);
fragment.setArguments(args);
return fragment;
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
String sortBy = getArguments().getString("sortBy", "");
// java.lang.NullPointerException in the previous line
// Attempt to invoke virtual method 'java.lang.String
// android.os.Bundle.getString(java.lang.String, java.lang.String)'
// on a null object reference
}
}
And inside MainActivity:
#Override
public boolean onOptionsItemSelected(#NonNull MenuItem item) {
int id = item.getItemId();
switch (id) {
case R.id.action_popular_movies:
PopularMoviesFragment fragment = PopularMoviesFragment.newInstance("popularity.desc");
getSupportFragmentManager().beginTransaction()
.replace(R.id.fragment_container, fragment)
.commit();
return true;
default:
return super.onOptionsItemSelected(item);
}
}

I tried the pasted code. It's weird that I didn't get the NullPointerException at all.
TestActivity.java :
package com.example.myapplication;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class TestActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
Button btn_test = findViewById(R.id.btn_test);
btn_test.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
testFragment();
}
});
}
private void testFragment() {
PopularMoviesFragment fragment = PopularMoviesFragment.newInstance("popularity.desc");
getSupportFragmentManager().beginTransaction()
.replace(R.id.container, fragment)
.commit();
}
}
activity_test.xml :
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
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">
<Button
android:text="test"
android:textSize="32sp"
android:textColor="#000"
android:id="#+id/btn_test"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<FrameLayout
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_weight="1"
android:layout_height="wrap_content"></FrameLayout>
</LinearLayout>
PopularMoviesFragment.java:
package com.example.myapplication;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.View;
public class PopularMoviesFragment extends Fragment {
public static PopularMoviesFragment newInstance(String sortBy) {
PopularMoviesFragment fragment = new PopularMoviesFragment();
Bundle args = new Bundle();
args.putString("sortBy", sortBy);
fragment.setArguments(args);
return fragment;
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
String sortBy = getArguments().getString("sortBy", "");
Log.i("test", "sortBy=" + sortBy);
}
}

Override onActivityCreated() method in your Fragment and retrieve the value of sortBy in this method using this line - String sortBy = getArguments().getString("sortBy", ""); instead of the onCreate() method.

Nested fragments - Screen of Frag2 stays empty

I'm suffering through nested fragments. I have a mainactivity which calls a fragment 1 which in turns call a fragment via a button. The fragment frag2 is well instantiated but the screen is blank.
Is there something obvious with my code?
MainActivity
import android.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FragmentManager fragmentManager;
Frag1 f1 = new Frag1();
fragmentManager = getFragmentManager();
fragmentManager.beginTransaction().replace(R.id.content_frame,
f1).commit();
}
}
mainactivity 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="com.narb.nestedfragments.MainActivity">
<FrameLayout
android:id="#+id/content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</RelativeLayout>
Fragment 1 and its xml layout:
import android.app.FragmentTransaction;
import android.content.Context;
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.RelativeLayout;
/**
* A simple {#link Fragment} subclass.
*/
public class Frag1 extends android.app.Fragment {
Context context;
private Button back1;
RelativeLayout rl1;
public Frag1() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootview = null;
rootview = inflater.inflate(R.layout.fragment_frag1, container, false);
return rootview;
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
context = getActivity().getApplicationContext();
initFindView();
back1.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Log.i("frag1","createdview");
//getActivity().getFragmentManager().popBackStackImmediate();
rl1.setVisibility(View.INVISIBLE);
FragmentTransaction ft = getFragmentManager().beginTransaction();
Frag2 f2 = new Frag2();
ft.replace(R.id.fl1, f2);
ft.addToBackStack(null);
ft.commit();
}
});
}
private void initFindView(){
back1 = (Button) getActivity().findViewById(R.id.btn1);
rl1 = (RelativeLayout) getActivity().findViewById(R.id.rl1);
}
}
Is it normal that I need to make my layout frag 1 invisible before calling frag2?
and finally my fragment 2 and its layout. I see the log for frag 2 but the screen is empty:
import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
public class Frag2 extends Fragment {
Context context;
private Button btn2;
public Frag2() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootview;
rootview = inflater.inflate(R.layout.fragment_frag2, container, false);
Log.i("frag2","createdview");
return rootview;
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
context = getActivity().getApplicationContext();
Log.i("frag2","onactivitycreated");
btn2 = (Button) getActivity().findViewById(R.id.btn2);
btn2.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Log.i("frag2","onactivitycreated");
}
});
}
}
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.narb.nestedfragments.Frag2">
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="Test 2" />
<Button
android:id="#+id/btn2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="60dp"
android:text="back"
/>
</RelativeLayout>

if your fragment 1 is having another FrameLayout where you are replacing fragment 2, then instead of getFragmentManager(), use getChildFragmentManager() in fragment 1
otherwise you are passing wrong container id in replace() method R.id.fl1 inside fragment1. you should pass R.id.content_frame there.

You have not posted the fragment1 XML Code. lets assume RelativeLayout (rl1) is your parent layout and you have FrameLayout (fl1) inside the rl1. You are making the parent layout invisible. So the fragment2 can't be visible.
If you don't want to show the fragment1 while showing there is no need for the nested fragment.
You should call like this to load second fragment.
getFragmentManager().beginTransaction()
.replace(R.id.content_frame ,new Frag2());
.addToBackStack(null);
.commit();

use content_frame id of activity_main in Frag1 class
back1.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Log.i("frag1", "createdview");
//getActivity().getFragmentManager().popBackStackImmediate();
rl1.setVisibility(View.INVISIBLE);
FragmentTransaction ft = getFragmentManager().beginTransaction();
Frag2 f2 = new Frag2();
ft.replace(R.id.content_frame, f2);
ft.addToBackStack(null);
ft.commit();
}
});

getSupportFragmentManager().findFragmentById() returns null even though fragment exists

I have a fragment_main.xml inside an activity_main.xml.
The fragment is added inside a Tabbed Activity created from an Android Studio template.
I want to do a change in the Fragment's view from within the Activity. That's why I created an Interface that allows the Fragment to call the Activity during the Fragment's onStart, when I know that the Fragment's view is available for modifications.
I did get this to work if I pass the actual Fragment instance using my interface callback. But I'm still frustrated because I don't understand why this function returns null. Does this have anything to do with reusing fragments in different screen orientations?
I've looked over similar questions here on SO reported with this function returning null. Somebody mentioned that there might be an issue with using import android.support.v4.app.Fragment; as opposed to just android.app.Fragment. I don't think this is my case because getsupportFragmentManager seems to return the correct type of Fragment (v4.app). I have no idea why the v4.app is there, I'm kinda new to all this.
Anyway here's the code, all of it, including imports, because they might be relevant.
package org.axonnsd.musicnexus;
import android.app.Activity;
import android.content.Context;
import android.media.MediaPlayer;
import android.os.Environment;
import android.os.Handler;
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.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.MediaController;
import android.widget.TextView;
import java.io.FileInputStream;
import java.io.IOException;
public class MainActivity extends AppCompatActivity implements OnFragmentReadyListener {
/**
* 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;
private static final String TAG = "MyTabbedApplication";
private Handler handler = new Handler();
/**
* The {#link ViewPager} that will host the section contents.
*/
private ViewPager mViewPager;
#Override
protected void onStop() {
super.onStop();
mediaController.hide();
mediaPlayer.stop();
mediaPlayer.release();
}
#Override
public boolean onTouchEvent(MotionEvent event) {
//the MediaController will hide after 3 seconds - tap the screen to make it appear again
mediaController.show();
return false;
}
public void onFragmentReady(PlaceholderFragment fragment)
{
this.getIntent().putExtra(AUDIO_FILE_NAME,AUDIO_FILE_NAME);
audioFile = this.getIntent().getStringExtra(AUDIO_FILE_NAME);
PlaceholderFragment fragment = (PlaceholderFragment)(getSupportFragmentManager().findFragmentById(R.id.main_audio_view));
//FRAGMENT IS NULL!
fragment.setNowPlayingText(audioFile);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
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());
// 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();
}
});
}
#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_main, 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);
}
/**
* 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";
private TextView _txtNowPlaying;
private MainActivity _parentActivity;
public PlaceholderFragment() {
}
/**
* Returns a new instance of this fragment for the given section
* number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
TextView textView = (TextView) rootView.findViewById(R.id.section_label);
_txtNowPlaying = (TextView)rootView.findViewById(R.id.now_playing_text);
textView.setText(getString(R.string.section_format, getArguments().getInt(ARG_SECTION_NUMBER)));
//notifyActivity(_parentActivity);
return rootView;
}
#Override
public void onAttach(Activity activity)
{
super.onAttach(activity);
_parentActivity = (MainActivity)activity;
}
#Override
public void onAttach(Context context)
{
super.onAttach(context);
if (context instanceof Activity){
_parentActivity = (MainActivity)context;
}
}
#Override
public void onStart()
{
super.onStart();
notifyActivity(_parentActivity);
}
private void notifyActivity(MainActivity activity)
{
activity.onFragmentReady(this);
}
public void setNowPlayingText(String value)
{
_txtNowPlaying.setText(value);
}
}
/**
* 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;
}
#Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "SECTION 1";
case 1:
return "SECTION 2";
case 2:
return "SECTION 3";
}
return null;
}
}
}
I'm pasting the XMLs too, even though they are fine (as I said, it works if I pass the actual fragment).
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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/main_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="org.axonnsd.musicnexus.MainActivity">
<android.support.design.widget.AppBarLayout
android:id="#+id/appbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="#dimen/appbar_padding_top"
android:theme="#style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:layout_scrollFlags="scroll|enterAlways"
app:popupTheme="#style/AppTheme.PopupOverlay">
</android.support.v7.widget.Toolbar>
</android.support.design.widget.AppBarLayout>
<android.support.v4.view.ViewPager
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="#string/appbar_scrolling_view_behavior" />
<android.support.design.widget.FloatingActionButton
android:id="#+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="end|bottom"
android:layout_margin="#dimen/fab_margin"
app:srcCompat="#android:drawable/ic_dialog_email" />
</android.support.design.widget.CoordinatorLayout>
fragment_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:id="#+id/main_audio_view"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="org.axonnsd.musicnexus.MainActivity$PlaceholderFragment">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="Now playing:"
android:textSize="25sp"
android:textStyle="bold"
/>
<TextView
android:id="#+id/now_playing_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="20dip"
android:layout_marginLeft="10dip"
android:layout_marginRight="10dip"
android:layout_gravity="center"
android:text="Now playing.."
android:textSize="16sp"
android:textStyle="italic"
/>
<TextView
android:id="#+id/section_label"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>

First of all, you're using findFragmentById wrong, passing id of root layout of your fragment as a parameter, when it expects an id of a layout that contains your fragment (not layout inside a fragment!)
FragmentPagerAdapter is kinda tricky and getting current fragment is not straightforward. Check this answer:
Getting the current Fragment instance in the viewpager
Replace your:
PlaceholderFragment fragment = (PlaceholderFragment)(getSupportFragmentManager().findFragmentById(R.id.main_audio_view));
//FRAGMENT IS NULL!
with
PlaceholderFragment page = (PlaceholderFragment)
getSupportFragmentManager().findFragmentByTag("android:switcher:" +
R.id.container + ":" + mViewPager.getCurrentItem());

I would try the following, but I'm sure it's not the nicest solution.
I would pass the value of section_number instead of the PlaceholderFragment and get the fragment from the SectionPageAdapter. Something like this:
public void onFragmentReady(int position)
{
this.getIntent().putExtra(AUDIO_FILE_NAME,AUDIO_FILE_NAME);
audioFile = this.getIntent().getStringExtra(AUDIO_FILE_NAME);
PlaceholderFragment fragment = (PlaceholderFragment)mSectionsPagerAdapter.getItem(position);
fragment.setNowPlayingText(audioFile);
}

Android ViewPager keeps crashing with NullPointerException on orientation change

I am trying to add a ViewPager to my Android app as a one-time setup screen for the user. But the problem I am facing is that the app keeps crashing when the orientation of the screen is changed amidst the setup process.
If the app is opened in either portrait or landscape mode and used without any orientation change, it works fine. But if the orientation is changed during runtime, using the method setCurrentItem(int position) on the ViewPager crashes the app.
Here's my Fragment class -
package com.cosine.arc;
import android.content.Context;
import android.graphics.Typeface;
import android.os.Bundle;
import android.support.v4.app.Fragment;
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.TextView;
/**
* A simple {#link Fragment} subclass.
*/
public class WelcomeFragment extends Fragment {
private int mPosition;
private Context mContext;
private ViewPager mPager;
private final int[] welcomeFragments = {R.layout.fragment_welcome1};
public WelcomeFragment() {
// Required empty public constructor
}
public WelcomeFragment(Context context, ViewPager viewPager, int position) {
this.mPosition = position;
this.mContext = context;
this.mPager = viewPager;
}
#Override
public View onCreateView(final LayoutInflater inflater, final ViewGroup container, Bundle savedInstanceState) {
View view = null;
try {
switch (mPosition) {
case 0:
view = inflater.inflate(R.layout.fragment_welcome1, container, false);
Typeface robotoLight = Typeface.createFromAsset(getActivity().getAssets(), "fonts/Roboto-Light.ttf");
TextView welcomeTxt1x2 = (TextView) view.findViewById(R.id.welcome_text_1_2);
Button startButton = (Button) view.findViewById(R.id.welcome_btn_1_1);
startButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
mPager.setCurrentItem(1);
}
});
welcomeTxt1x2.setTypeface(robotoLight);
}
} catch (NullPointerException e) {
e.printStackTrace();
}
return view;
}
}
And here's my FragmentActivity class with the FragmentStatePagerAdapter class within it -
package com.cosine.arc;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.PagerAdapter;
public class IntroActivity extends FragmentActivity {
private static int NUM_PAGES = 3;
private NonSwipeableViewPager mPager;
private PagerAdapter mPagerAdapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_intro);
mPager = (NonSwipeableViewPager) findViewById(R.id.intro_pager);
mPagerAdapter = new IntroSliderAdapter(getSupportFragmentManager());
mPager.setAdapter(mPagerAdapter);
}
#Override
public void onBackPressed() {
if (mPager.getCurrentItem()==0) {
super.onBackPressed();
}
else {
mPager.setCurrentItem(mPager.getCurrentItem()-1);
}
}
public int getCurrentItem() {
return mPager.getCurrentItem();
}
public NonSwipeableViewPager getPagerUpdate() {
return mPager;
}
private class IntroSliderAdapter extends FragmentStatePagerAdapter {
public IntroSliderAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
return new WelcomeFragment(getBaseContext(), mPager, position);
}
#Override
public int getCount() {
return NUM_PAGES;
}
}
}
And here is the error log -
04-07 15:25:13.774 12186-12186/com.cosine.arc E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.cosine.arc, PID: 12186 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setCurrentItem(int)' on a null object reference
at com.cosine.arc.WelcomeFragment$1.onClick(WelcomeFragment.java:58)
at android.view.View.performClick(View.java:5612)
at android.view.View$PerformClick.run(View.java:22288)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6123)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:757)
fragment_welcome1.xml -
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.cosine.arc.WelcomeFragment">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/colorPrimary">
<TextView
android:id="#+id/welcome_text_1_1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="#string/welcome_to_"
android:textColor="#android:color/white"
android:textSize="36sp"
android:padding="16dp"
android:layout_marginTop="16dp"
android:gravity="center"/>
<ImageView
android:id="#+id/welcome_img_1_1"
android:layout_width="150dp"
android:layout_height="150dp"
android:src="#drawable/ic_logo"
android:layout_below="#id/welcome_text_1_1"
android:layout_centerHorizontal="true"/>
<TextView
android:id="#+id/welcome_text_1_2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="#id/welcome_img_1_1"
android:text="#string/lets_get_things_started_"
android:textSize="42sp"
android:textColor="#android:color/white"
android:padding="16dp"
android:layout_marginTop="32dp"/>
<Button
android:id="#+id/welcome_btn_1_1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:background="#android:color/white"
android:text="Start"
android:textColor="#android:color/black"
android:layout_margin="16dp"
android:layout_alignParentRight="true"
android:drawableRight="#mipmap/ic_arrow_right_light"/>
</RelativeLayout>
Please do note that I have two different layout files fragment_welcome1.xml and fragment_welcome1.xml-land.

On orientation change, you will have to save the instance of the fragment if you want to retain the references. Have a look at this answer, hope it helps you. In a nutshell, i think you will need to save the instance of the fragment in your container activity's onSaveInstanceState(), and then recreate your saved fragment when orientation changes.
Please note that making config changes in the manifest is not the recommended way to save the instance of the fragment. Making config changes will lead to memory leaks.

Updating a textView/s in a fragment from an Activity (using ViewPager)

I'm constantly receiving data in MainActivity and I need it to only be written a textView when the fragment that contains the textView is inflated. Obviously the app crashes if I try to write to a textView that is in a fragment currently not in display. I have made a dummy activity to explain my problem and I'm using a countdown timer to represent the data that is continually changing in the MainActivity. The issue resides in MainActivity.
Would someone mind explaining how I can only write to the textView when it is inflated?
Thanks
FragmentA.java (Fragment B and C are almost identical)
package com.felhr.scrolltabs;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
/**
* Created by Luke on 20/04/2015.
*/
public class FragmentA extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_a, container, false);
}
}
MainActivity.java
package com.felhr.scrolltabs;
import android.os.Bundle;
import android.os.CountDownTimer;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.widget.TextView;
public class MainActivity extends FragmentActivity {
ViewPager viewPager = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager = (ViewPager)findViewById(R.id.pager);
FragmentManager fragmentManager = getSupportFragmentManager();
viewPager.setAdapter(new MyAdapter(fragmentManager));
final TextView timer = (TextView)findViewById(R.id.textViewTimer);
// Countdown timer code -> to be run constantly but only displayed in Fragment A is in focus
// This section breaks the code
new CountDownTimer(30000, 1000) {
public void onTick(long millisUntilFinished) {
timer.setText("seconds remaining: " + millisUntilFinished / 1000);
}
public void onFinish() {
timer.setText("done!");
}
}.start();
}
}
class MyAdapter extends FragmentPagerAdapter
{
public MyAdapter(FragmentManager fm)
{
super(fm);
}
#Override
public Fragment getItem(int i) {
Fragment fragment = null;
Log.d("SWIPE","get Item is called"+i);
if (i==0)
{
fragment=new FragmentA();
}
if (i==1)
{
fragment=new FragmentB();
}
if (i==2)
{
fragment=new FragmentC();
}
return fragment;
}
#Override
public int getCount() {
Log.d("SWIPE","get count is called");
return 3;
}
// talks to title to give the page
#Override
public CharSequence getPageTitle(int position) {
if (position == 0) {
return "Tab 1";
}
if (position == 1) {
return "Tab 2";
}
if (position == 2) {
return "Tab 3";
}
return null;
}
}
fragment_a.xml (fragments b and c are almost identical)
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#C3f3f3">
<TextView
android:id="#+id/textViewTimer"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="Fragment A"
android:textColor="#000000"
android:gravity="center"/>
</RelativeLayout>
activity_main.xml
<android.support.v4.view.ViewPager
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/pager">
<android.support.v4.view.PagerTitleStrip
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/title"
android:background="#33B5E5">
</android.support.v4.view.PagerTitleStrip>
</android.support.v4.view.ViewPager>

Develop Reference

The Android operating system is a mobile operating system that was developed by Google (GOOGL?) to be primarily used for touchscreen devices, cell phones, and tablets.

Access a method of a Fragment from the ViewPager Activity - android

Best way to do this, just call CallingFragmentName fragment = (CallingFragmentName) viewPager .getAdapter() .instantiateItem(viewPager, viewPager.getCurrentItem()); It will re-instantiate your calling Fragment, so that it will not throw null pointer exception.

Related

Android: getArguments() in Fragment returns null, even though I setArguments() inside newInstance()

Nested fragments - Screen of Frag2 stays empty

getSupportFragmentManager().findFragmentById() returns null even though fragment exists

Android ViewPager keeps crashing with NullPointerException on orientation change

Updating a textView/s in a fragment from an Activity (using ViewPager)

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