Develop Reference

How to call NavController from fragment?

In my fragment_main.xml, I have the following code :
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.fragment.app.FragmentContainerView
android:id="#+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:layout_constraintBottom_toTopOf="#+id/bottomBar"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph='#navigation/bottom_bar_nav_graph' />
<!--custom bottom navigation ui-->
</androidx.constraintlayout.widget.ConstraintLayout>
I would like to have access to navController(***bottom_bar_nav_graph***) from fragment.
Is it possible?

If I get what you are trying to do correctly, you what to do something like
findViewbyId(R.id.bottom_bar_nav_graph)
which is not possible.
What this line of code is doing
app:navGraph='#navigation/bottom_bar_nav_graph'
is to let FragmentContainerView know about your graph bottom_bar_nav_graph which is an XML file that describes how your fragments relate, pass data and navigate between each other.
But can have access to nav_host_fragment which is the id for the host fragment.
If you want to access the navController with the id in Activity, you can use
val navController = findNavController(R.id.nav_host_fragment)

extends Fragment {
private static final String ARG_SECTION_NUMBER = "section_number";
private PageViewModel pageViewModel;
private FragmentMainBinding binding;
public static PlaceholderFragment newInstance(int index) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle bundle = new Bundle();
bundle.putInt(ARG_SECTION_NUMBER, index);
fragment.setArguments(bundle);
return fragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
pageViewModel = new ViewModelProvider(this).get(PageViewModel.class);
int index = 1;
if (getArguments() != null) {
index = getArguments().getInt(ARG_SECTION_NUMBER);
}
pageViewModel.setIndex(index);
}
#Override
public View onCreateView(
#NonNull LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
binding = FragmentMainBinding.inflate(inflater, container, false);
View root = binding.getRoot();
final TextView textView = binding.sectionLabel;
pageViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
#Override
public void onChanged(#Nullable String s) {
textView.setText(s);
}
});
return root;
}

Sending data from Fragment to Fragment using Interface, by setting Fragment Layouts dynamically. Saved instance of Fragment NOT working

I am sending data from one fragment to another, using interface. This works absolutely fine. Now I am trying to use onSaveInstanceState() to save the value in
a Fragment and retrieving in onCreate(). however i'm getting null in Bundle of onCreate(). P.S. everything works fine when i set the Fragment directly into the activity layout in xml. but when i set the fragment through java code into the activity, the onSaveInstanceState is failing. It is not saving the last known value. Please help. Pasting the code below. You can try it out to know the exact issue.
Fragment_A :
public class Fragment_A extends Fragment implements View.OnClickListener {
Button btnAdd;
int counter = 0;
Communicator comm;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState != null){
counter = savedInstanceState.getInt("counter", 0);
}
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_a, container, false);
return view;
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
comm = (Communicator) getActivity();
btnAdd = (Button) getActivity().findViewById(R.id.btnAdd);
btnAdd.setOnClickListener(this);
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("counter", counter);
}
#Override
public void onClick(View v) {
counter++;
comm.sendData(counter);
}
}
interface Communicator{
void sendData(int i);
}
=====
Activity :
public class Activity_InterComm extends Activity implements Communicator{
FragmentManager manager;
FragmentTransaction transaction;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_intercomm);
Fragment_A fragment_1 = new Fragment_A();
Fragment_B fragment_2 = new Fragment_B();
manager = getFragmentManager();
transaction = manager.beginTransaction();
transaction.add(R.id.frag_a, fragment_1, "Frag1");
transaction.add(R.id.frag_b, fragment_2, "Frag2");
transaction.commit();
}
#Override
public void sendData(int i) {
manager = getFragmentManager();
Fragment_B fragment_b = (Fragment_B) manager.findFragmentById(R.id.frag_b);
fragment_b.setData("Button has been clicked " + i + " times");
}
}
=====
Fragment_B :
public class Fragment_B extends Fragment {
TextView txtMessage;
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_b, container, false);
return view;
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
txtMessage = (TextView) getActivity().findViewById(R.id.txtMessage);
}
public void setData(String message){
txtMessage.setText(message);
}
}
activity_intercomm.xml :
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<!--<fragment
android:id="#+id/frag_a"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_marginBottom="8dp"
android:layout_weight="1"
android:name="android.learning.com.fragintercomm.Fragment_A"/>
<fragment
android:id="#+id/frag_b"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
android:name="android.learning.com.fragintercomm.Fragment_B"/>-->
<LinearLayout
android:id="#+id/frag_a"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_marginBottom="8dp"
android:layout_weight="1"
android:background="#color/colorAccent"
android:orientation="vertical"/>
<LinearLayout
android:id="#+id/frag_b"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_marginBottom="8dp"
android:layout_weight="1"
android:background="#color/colorPrimaryDark"
android:orientation="vertical"/>
</LinearLayout>

the soluion I found was using getView() instead of getActivity() while initializing the button in Fragment_A. use btnAdd = (Button) getView().findViewById(R.id.btnAdd); instead of btnAdd = (Button) getActivity().findViewById(R.id.btnAdd);.
However, you can't use getView() in Fragment_B. The Textview freezes and, onSaveInstanceStat() doesn't work. Please suggest a solution.

Layout for tablets using two fragments

I am doing a sample project as an excercise and want to display two fragments in the same activity when dealing with tablets(7' and 10').
So what I have so far is this.
As you can see I can display the data of my recyclerview in the left (static) fragment. However the right fragment is empty.
So I have two questions.
1) How to display by default in the right fragment the data of the first row of recyclerview?(ie image and article)
2) How to implement the click listener and update the right fragment?
Here is my code:
MainActivity
public class MainActivity extends AppCompatActivity {
private boolean mTwoPane;
private static final String DETAIL_FRAGMENT_TAG = "DFTAG";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(findViewById(R.id.detailed_match_reports)!=null) {
mTwoPane = true;
if (savedInstanceState == null) {
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.detailed_match_reports, new DetailedActivityFragment(),DETAIL_FRAGMENT_TAG)
.commit();
}else{
mTwoPane = false;
}
}
}
}
layout/activity_main.xml
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/match_reports"
android:name="theo.testing.androidservices.fragments.MainActivityFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="16dp"
android:layout_marginRight="16dp"
tools:context="theo.testing.androidservices.activities.MainActivity"
tools:layout="#android:layout/list_content" />
layout-sw600dp/activity_main
<LinearLayout 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"
android:baselineAligned="false"
android:divider="?android:attr/dividerHorizontal"
android:orientation="horizontal"
tools:context="theo.testing.androidservices.activities.MainActivity">
<fragment
android:id="#+id/match_reports"
android:name="theo.testing.androidservices.fragments.MainActivityFragment"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="2"
tools:layout="#android:layout/list_content" />
<FrameLayout
android:id="#+id/detailed_match_reports"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="4" />
</LinearLayout>
MainActivityFragment
public class MainActivityFragment extends Fragment {
public static final String TAG = "AelApp";
public static ArrayList<MyModel> listItemsList;
RecyclerView myList;
public static MatchReportsAdapter adapter;
public MainActivityFragment() {
// Required empty public constructor
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
updateMatchReport();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
getActivity().setTitle("Match Report");
View rootView = inflater.inflate(R.layout.fragment_main_activity, container, false);
listItemsList = new ArrayList<>();
myList = (RecyclerView)rootView.findViewById(R.id.listview_match_reports);
final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
myList.setHasFixedSize(true);
myList.setLayoutManager(linearLayoutManager);
adapter = new MatchReportsAdapter(getActivity(), listItemsList);
myList.setAdapter(adapter);
return rootView;
}
public void updateMatchReport(){
Intent i = new Intent(getActivity(), MatchReport.class);
getActivity().startService(i);
}
}

First let me answer the second question. To show a fragment on the right side of the screen add something like this (note how I'm using that id of the frame layout to replace the fragment):
Fragment fragment = new MyRightSideFragment();
FragmentManager fm = getFragmentManager();
fm.beginTransaction().replace(R.id.detailed_match_reports, fragment).commit();
Now, for the first question, you need to implement click listener, you can find an example here.
public class ReactiveAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
#Override
public void onBindViewHolder(final ViewHolder holder, int position) {
holder.itemView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
int position = (Integer)v.getTag();
showDetail(position);
}
});
}
}
Notice that I'm using the tag of the view to identify the position (so somwhere in your onBindViewHolder code you must set this tag).
public function showDetail(int position) {
... show fragment por position
}
and finally, when your in your OnCreateView or somewhere in your setup code, call showDetail(0).

My views are giving me a null pointer exception

In my app,I get some data from my server. They are displayed fine,but when I pass them in my Detailed Fragment,then all views are null:(.
So here is my code.
public class MainActivityFragment extends Fragment {
public static final String TAG = "AelApp";
public static ArrayList<MyModel> listItemsList;
RecyclerView myList;
public static MatchReportsAdapter adapter;
public MainActivityFragment() {
// Required empty public constructor
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
updateMatchReport();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
getActivity().setTitle("Match Report");
View rootView = inflater.inflate(R.layout.fragment_main_activity, container, false);
listItemsList = new ArrayList<>();
myList = (RecyclerView)rootView.findViewById(R.id.listview_match_reports);
final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
myList.setHasFixedSize(true);
myList.setLayoutManager(linearLayoutManager);
adapter = new MatchReportsAdapter(getActivity(), listItemsList);
myList.setAdapter(adapter);
return rootView;
}
public void updateMatchReport(){
Intent i = new Intent(getActivity(), MatchReport.class);
getActivity().startService(i);
}
}
Adapter
public class MatchReportsAdapter extends
RecyclerView.Adapter<MatchReportsAdapter.RowHolder>{
private List<MyModel> reportsList;
private Context mContext;
private ImageLoader mImageLoader;
private int focused = 0;
public MatchReportsAdapter(Activity activity, List<MyModel> reportsLists){
this.reportsList = reportsLists;
this.mContext=activity;
}
#Override
public RowHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.row_items,null);
final RowHolder holder = new RowHolder(v);
return holder;
}
#Override
public void onBindViewHolder(RowHolder holder, int position) {
final MyModel listItems = reportsList.get(position);
holder.itemView.setSelected(focused==position);
holder.getLayoutPosition();
mImageLoader = AppController.getInstance().getImageLoader();
holder.thumbnail.setImageUrl(listItems.getImage(),mImageLoader);
holder.thumbnail.setDefaultImageResId(R.drawable.reddit_placeholder);
holder.name.setText(Html.fromHtml(listItems.getTitle()));
holder.relativeLayout.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
String article = listItems.getArticle();
String image = listItems.getImage();
Intent i = new Intent(mContext, DetailedActivity.class);
i.putExtra("articleKey",article);
i.putExtra("imageKey",image);
mContext.startActivity(i);
}
});
}
#Override
public int getItemCount() {
return reportsList.size();
}
public class RowHolder extends RecyclerView.ViewHolder{
protected NetworkImageView thumbnail;
protected TextView name;
protected RelativeLayout relativeLayout;
public RowHolder(View itemView) {
super(itemView);
this.relativeLayout = (RelativeLayout)
itemView.findViewById(R.id.recLayout);
this.thumbnail =
(NetworkImageView)itemView.findViewById(R.id.thumbnail);
this.name = (TextView)itemView.findViewById(R.id.title);
}
}
}
DetailedActivity
public class DetailedActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detailed);
if(savedInstanceState == null){
getSupportFragmentManager()
.beginTransaction()
.add(R.id.detailed_match_reports,new DetailedActivityFragment())
.commit();
}
}
}
DetailedActivityFragment
public class DetailedActivityFragment extends Fragment {
TextView articleTextView;
String image;
String article;
ImageView imageView;
public DetailedActivityFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v = inflater.inflate(R.layout.fragment_detailed_activity, container, false);
articleTextView = (TextView)getActivity().findViewById(R.id.articleTextView);
imageView = (ImageView)getActivity().findViewById(R.id.imageNews);
Intent i = getActivity().getIntent();
article = i.getStringExtra("articleKey");
image = i.getStringExtra("imageKey");
Picasso.with(getActivity()).load(image).into(imageView);
articleTextView.setText(article);
return v;
}
}
All of my data are passed after clicking a row good. I know this as I debug the following lines.
article = i.getStringExtra("articleKey");
image = i.getStringExtra("imageKey");
and see that both String variables are not null. However,the both views(TextView,ImageView) of my detailed fragment are null.
Maybe I am doing something wrong with my xml file,and I don't see it.
activity_main.xml
<FrameLayout 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"
android:id="#+id/match_reports"
tools:context="theo.testing.androidservices.fragments.MainActivityFragment">
</FrameLayout>
fragment_main_activity
<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"
android:id="#+id/recLayout"
tools:context=".activities.MainActivity"
android:background="#fff">
<android.support.v7.widget.RecyclerView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="#+id/listview_match_reports"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
/>
</RelativeLayout>
activity_detailed.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/detailed_match_reports"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="theo.testing.androidservices.activities.DetailedActivity"
tools:ignore="MergeRootFrame">
</FrameLayout>
and finally
fragment_detailed_activity
<?xml version="1.0" encoding="utf-8"?>
<ScrollView android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="#+id/imageNews"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
xmlns:android="http://schemas.android.com/apk/res/android">
<TextView
android:layout_gravity="center_horizontal"
android:padding="10dp"
android:text="xcvxcvxcv"
android:textColor="#000"
android:layout_marginTop="5dp"
android:textAppearance="?android:attr/textAppearanceMedium"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/articleTextView"/>
</ScrollView>
What am I missing?
Thanks
Theo.

Change these
articleTextView = (TextView)getActivity().findViewById(R.id.articleTextView);
imageView = (ImageView)getActivity().findViewById(R.id.imageNews);
to
articleTextView = (TextView)v.findViewById(R.id.articleTextView);
imageView = (ImageView)v.findViewById(R.id.imageNews);
You'r passing data to DetailActivity. So first retrieve in DetailActivity and then pass to DetailFragment.
Also you need to pass data to DetailFragment using Bundle with setArguments(bundle)

Your Textview articleTextView is in the fragment but you are finding it in the activitys xml:
articleTextView = (TextView)getActivity().findViewById(R.id.articleTextView);
insetad you should do:
articleTextView = (TextView)(v.findViewById(R.id.articleTextView));
Do the same for Imageviewl.

NullPointerException when trying to use a listener for FAB

I'm trying to put a FAB in a ViewPager tab, but I get this error (and only this):
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
It was wroking fine when I had the FAB in the activity_main.xml
MainActiviy:
private FloatingActionButton fabButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
...
// Initializing Floating Action Button
fabButton = (FloatingActionButton) findViewById(R.id.fabButton);
fabButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Snackbar.make(v, "FAB was pressed!", Snackbar.LENGTH_SHORT)
.setAction("Undo", new View.OnClickListener() {
#Override
public void onClick(View v) {
}
})
.show();
}
});
...
}
PageFragment used to sort the different tabs:
public class PageFragment extends Fragment {
public static final String ARG_PAGE = "ARG_PAGE";
private int mPage;
public static PageFragment newInstance(int page) {
Bundle args = new Bundle();
args.putInt(ARG_PAGE, page);
PageFragment fragment = new PageFragment();
fragment.setArguments(args);
return fragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mPage = getArguments().getInt(ARG_PAGE);
System.out.println(">> mPage = " + mPage); //Testing
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
SampleFragmentPagerAdapter sampleFragmentPagerAdapter = new SampleFragmentPagerAdapter(getFragmentManager(), getContext());
View view;
switch (mPage) {
case 1:
view = inflater.inflate(R.layout.tab1_frag, container, false);
return view;
case 2:
view = inflater.inflate(R.layout.tab2_frag, container, false);
return view;
case 3:
view = inflater.inflate(R.layout.tab3_frag, container, false);
return view;
default:
view = inflater.inflate(R.layout.fragment_page, container, false);
return view;
}
}
}
tab_2frag xml file for the particular tab:
<?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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical">
<FrameLayout
android:id="#+id/frame"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="Tab 2"
android:textSize="40sp" />
<android.support.design.widget.FloatingActionButton
android:id="#+id/fabButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_marginBottom="#dimen/fab_margin_bottom"
android:layout_marginEnd="#dimen/fab_margin_end"
android:src="#mipmap/ic_add_white_24dp"
app:fabSize="normal" />
</FrameLayout>
can anyone help?

Dont use listener.
In your xml:
android:onClick:"nameOfMethod"
In your Activity:
public void nameofMethod(View v){
//button Clicked
}

Your FloatingActionButton is in a fragment layout, but you are trying to find it in the MainActivity's onCreate(). findViewById(R.id.fabButton) returns null and thus causing the error when you set a click listener on it in the MainActivity.
You may call it in the onCreateView() of the fragment instead if you want to do it programatically
view = inflater.inflate(R.layout.tab2_frag, container, false);
fabButton = (FloatingActionButton) view.findViewById(R.id.fabButton);
fabButton.setOnClickListener(new View.OnClickListener() {...} );
return view;