I have created an experimental app in which I'm trying to learn to establish a successful communication b/w two fragments.
What I have is just one activity which is Main Activity. In this activity I have a view pager element in XML. I've created custom pager adapter which extends to Fragment Pager Adapter and two Fragments which are children and supplied by my pager adapter to the view pager.
What I'm trying to do is: FirstFragment has one button which on clicked changes the background color of the SecondFragment(there's a relative layout as parent), which will be visible on one swipe.
What I've done so far: I created an interface in FirstFragment, implemented in MainActivity, created a method in SecondFragment which changes the background color of layout and finally getting the SecondFragment in MainActivvity (at least trying to) and calling its method. But app is crashing on button click saying "Fragment SecondFragment not attached to a context"
Here's the code:
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
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=".MainActivity">
<android.support.v4.view.ViewPager
android:id="#+id/view_pager"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</android.support.constraint.ConstraintLayout>
MainActivity.java
package com.example.android.laboratory;
import...
public class MainActivity extends AppCompatActivity implements FirstFragment.MyListener {
ViewPager viewPager;
MyPagerAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager = findViewById(R.id.view_pager);
adapter = new MyPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(adapter);
}
#Override
public void changeColor() {
SecondFragment secondFragment = new SecondFragment();
secondFragment.changeColor();
}
}
Custom Adapter:
package com.example.android.laboratory;
import ...
public class MyPagerAdapter extends FragmentPagerAdapter {
public MyPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int i) {
switch (i) {
case 0:
return new FirstFragment();
case 1:
return new SecondFragment();
}
return null;
}
#Override
public int getCount() {
return 2;
}
}
First Fragment:
package com.example.android.laboratory;
import ...
public class FirstFragment extends Fragment {
MyListener listener;
public FirstFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_first, container, false);
Button button = view.findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
listener.changeColor();
}
});
return view;
}
public interface MyListener{
void changeColor();
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
try {
listener = (MyListener) context;
} catch (ClassCastException e) {
throw new ClassCastException(getActivity().toString() + " must implement MyListener interface.");
}
}
}
Second Fragment:
package com.example.android.laboratory;
import ...
public class SecondFragment extends Fragment {
RelativeLayout relativeLayout;
public SecondFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_second, container, false);
relativeLayout = view.findViewById(R.id.layout);
return view;
}
public void changeColor() {
relativeLayout.setBackgroundColor(getResources().getColor(R.color.colorAccent));
}
}
Crash log:
12-23 12:18:03.574 31428-31428/com.example.android.laboratory E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.laboratory, PID: 31428
java.lang.IllegalStateException: Fragment SecondFragment{2bfa6ff2} not attached to a context.
at android.support.v4.app.Fragment.requireContext(Fragment.java:696)
at android.support.v4.app.Fragment.getResources(Fragment.java:760)
at com.example.android.laboratory.SecondFragment.changeColor(SecondFragment.java:32)
at com.example.android.laboratory.MainActivity.changeColor(MainActivity.java:28)
at com.example.android.laboratory.FirstFragment$1.onClick(FirstFragment.java:31)
at android.view.View.performClick(View.java:4791)
at android.view.View$PerformClick.run(View.java:19903)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5296)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:912)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:707)
You can see this doc https://developer.android.com/training/basics/fragments/communicating
If you want to make you own bicycle for some reasons, you could try something like this (observer pattern)
MyModel
import java.util.ArrayList;
public class MyModel {
private int color = R.color.colorPrimary;
private ArrayList<MyObserver> observers = new ArrayList<>();
interface MyObserver {
void setColor(int color);
}
public void setColor(int color) {
this.color = color;
for (int i = 0; i < observers.size(); i++) {
observers.get(i).setColor(color);
}
}
public void addObserver(MyObserver newObserver) {
if (observers.indexOf(newObserver) < 0) {
observers.add(newObserver);
}
}
public void deleteObserver(MyObserver oldObserver) {
if (observers.indexOf(oldObserver) > -1) {
observers.remove(oldObserver);
}
}
}
FirstFragment
public class FirstFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_first, container, false);
Button button = view.findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
MainActivity mainActivity = (MainActivity) getActivity();
mainActivity.myModel.setColor(R.color.colorAccent);
}
});
return view;
}
}
SecondFragment
public class SecondFragment extends Fragment implements MyModel.MyObserver {
RelativeLayout relativeLayout;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_second, container, false);
relativeLayout = view.findViewById(R.id.layout);
MainActivity mainActivity = (MainActivity) getActivity();
mainActivity.myModel.addObserver(this);
return view;
}
#Override
public void onDestroy() {
MainActivity mainActivity = (MainActivity) getActivity();
mainActivity.myModel.deleteObserver(this);
super.onDestroy();
}
#Override
public void setColor(int color) {
relativeLayout.setBackgroundColor(getResources().getColor(color, null));
}
}
MainActivity
public class MainActivity extends AppCompatActivity {
ViewPager viewPager;
MyPagerAdapter adapter;
public MyModel myModel = new MyModel();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager = findViewById(R.id.view_pager);
adapter = new MyPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(adapter);
}
}
Related
I am trying to replace the current active fragment inside ViewPager when item inside fragment's recycelerview is clicked. So far, I manage to pop up the Toast on the second fragment when the item on the first fragment is clicked, but the all the view of the second fragment is blank.
Here is my code:
MainActivity.class
public class MainActivity extends AppCompatActivity {
private ViewPager viewPager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
viewPager = findViewById(R.id.view_pager);
FragmentAdapter adapter = new FragmentAdapter(getSupportFragmentManager());
viewPager.setAdapter(adapter);
viewPager.setOffscreenPageLimit(adapter.getCount() - 1);
}
// ..........
private static class FragmentAdapter extends FragmentStatePagerAdapter {
public FragmentAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return AllGenreFragment.newInstance();
case 1:
return DashboardFragment.newInstance();
case 2:
return NotificationFragment.newInstance();
}
return null;
}
#Override
public int getCount() {
return 3;
}
}
// ..........
}
AllGenreFragment.class
public class AllGenreFragment extends Fragment {
RecyclerView genreRV;
private AllGenreAdapter allGenreAdapter;
private List<Genre> genreList;
public static AllGenreFragment newInstance() {
return new AllGenreFragment();
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setHasOptionsMenu(true);
}
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_genre, container, false);
genreRV = v.findViewById(R.id.rv);
genreRV.setHasFixedSize(true);
GridLayoutManager layoutManager = new GridLayoutManager(getContext(), 2);
genreRV.setLayoutManager(layoutManager);
genreList = new ArrayList<>();
allGenreAdapter = new AllGenreAdapter(genreList, getContext());
genreRV.setAdapter(allGenreAdapter);
return v;
}
}
AllGenreAdapter.class
public class AllGenreAdapter extends RecyclerView.Adapter<AllGenreAdapter.ViewHolder> {
// .......
class ViewHolder extends android.support.v7.widget.RecyclerView.ViewHolder {
public ViewHolder(final View itemView) {
super(itemView);
itemView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(context, "Genre: " + genre_title.getText().toString(), Toast.LENGTH_SHORT).show();
AppCompatActivity activity = (AppCompatActivity) itemView.getContext();
FragmentManager fragmentManager = activity.getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
Fragment allAnimeFragment = new AllAnimeFragment();
Bundle bundle = new Bundle();
bundle.putString("genreid", genre_id.getText().toString().trim());
allAnimeFragment.setArguments(bundle);
fragmentTransaction.replace(R.id.view_pager, allAnimeFragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
}
});
}
}
// .......
}
AllAnimeFragment.class
public class AllAnimeFragment extends Fragment {
RecyclerView animeRV;
private AllAnimeAdapter allAnimeAdapter;
private List<Anime> animeList;
String genreid;
public static AllAnimeFragment newInstance() {
return new AllAnimeFragment();
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setHasOptionsMenu(true);
}
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_anime, container, false);
Bundle arguments = getArguments();
genreid = arguments.getString("genreid");
Toast.makeText(getContext(), genreid, Toast.LENGTH_SHORT).show();
// .....
return v;
}
}
Your approach is not really good, try below way:
Create a container fragment, called ContainerFragment, example, you will be using this fragment for your ViewPager.
The ContainerFragment should contain a container view, and add AllGenreFragment in the first them it is invoked.
In AllGenreFragment, create a callback, when an item in the RecyclerView be clicked, then in ContainerFragment will replace (or add) current fragment (AllGenreFragment) to AllAnimeFragment
First, create ContainerFragment,
public class ContainerFragment extends Fragment implements AllGenreFragment.OnAllGenreFragmentListener {
#Nullable #Override public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_container, container, false);
}
#Override public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
initialLoad();
}
private void initialLoad() {
getChildFragmentManager()
.beginTransaction()
.add(R.id.container, AllGenreFragment.newInstance())
.commit();
}
#Override public void onItemClicked() {
getChildFragmentManager()
.beginTransaction()
.replace(R.id.container, AllAnimeFragment.newInstance())
.commit();
}
}
This Fragment should implement a callback from AllGenreFragment for handling fragment transaction.
also, the xml layout
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
Next step, add above fragment into ViewPager, we using ContainerFragment instead of AllGenreFragment.
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return ContainerFragment().newInstance();
case 1:
return DashboardFragment.newInstance();
case 2:
return NotificationFragment.newInstance();
}
return null;
}
Ok, so now come back to AllGenreFragment, we should create a CallBack that we implement in ContainerFragment
public interface AllGenreFragmentListener {
onItemClicked();
}
and then,
private AllGenreFragmentListener listener;
#Override public void onAttach(Context context) {
super.onAttach(context);
if (getParentFragment() instanceof AllGenreFragmentListener) {
listener = (AllGenreFragmentListener) getParentFragment();
}
}
so we have an instance of AllGenreFragmentListener, from now, whenever listener call onItemClicked, the method onItemClicked in ContainerFragment will be invoked.
Ok, let do it,
create below variable and method in your AllGenreAdapter:
private AllGenreFragmentListener listener;
public void setListener(AllGenreFragmentListener listener) {
this.listener = listener;
}
and update your ViewHodler
itemView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(context, "Genre: " + genre_title.getText().toString(), Toast.LENGTH_SHORT).show();
if (listener != null)
listener.onItemClicked()
});
}
Don't forget call setListener method in your AllGenreFragment, so please add
#Override public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
if (allGenreAdapter != null) allGenreAdapter.setListener(listener);
}
That all,
I type this code by hand, not in my IDE so maybe it not compile, so please fix it if you face any compile error.
Note
If you want to keep the behavior of the BACK button, override onBackPressed in your MainActivity
#Override public void onBackPressed() {
Fragment f = getCurrentFragment();
if (f != null) {
if (f.getChildFragmentManager().getBackStackEntryCount() > 1) {
f.getChildFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
} else {
super.onBackPressed();
}
}
public Fragment getCurrentFragment() {
return (Fragment) viewPager.getAdapter()
.instantiateItem(viewPager, viewPager.getCurrentItem());
}
Also, add fragment into backStack whenever we add them to the container view (in your ContainerFragment)
private void initialLoad() {
getChildFragmentManager()
.beginTransaction()
.add(R.id.container, AllGenreFragment.newInstance())
.addToBackStack(null)
.commit();
}
#Override public void onItemClicked() {
// change `replace` to `add` and add more `.addToBackStack(null)`
getChildFragmentManager()
.beginTransaction()
.add(R.id.container, AllAnimeFragment.newInstance())
.addToBackStack(null)
.commit();
}
you should add a context in the constructor of your adapter
public class AllGenreAdapter(Context context) extends RecyclerView.Adapter<AllGenreAdapter.ViewHolder> {
// .......
}
then pass your activity to your adapter, use it to replace your fragment
EDIT:
I'm new in android and i try to use fragments in my app. I try to use a fragment function in my activity but i got a null pointer exception..
Fragment:
public class VideoviewFragment extends Fragment {
private View card;
public static VideoviewFragment create() {
return new VideoviewFragment();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_videoview, container, false);
card = (View) view.findViewById(R.id.card_video);
return view;
}
public void setalphacard(float value){
card.setAlpha(value);
}
}
In main activity i want to do that for example (i simplified my code):
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Viewpager
final SmartFragmentStatePagerAdapter adapterViewPager;
final ViewPager viewPager = (ViewPager) findViewById(R.id.am_view_pager);
adapterViewPager = new MainPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(adapterViewPager);
final VideoviewFragment videoviewFragment = (VideoviewFragment) adapterViewPager.getRegisteredFragment(2);
videoviewFragment.setalphacard(0.3f);
}
}
Main pager adapter:
public class MainPagerAdapter extends SmartFragmentStatePagerAdapter {
public MainPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch (position){
case 0:
return CameraFragment.create();
case 1:
return OptionFragment.create();
case 2:
return VideoviewFragment.create();
}
return null;
}
#Override
public int getCount() {
return 3;
}
}
You just have to declare the View globally like this:
public class VideoviewFragment extends Fragment {
private View card;
public static VideoviewFragment create() {
return new VideoviewFragment();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_videoview, container, false);
card = (View) view.findViewById(R.id.card_video);
return view;
}
public void setalphacard(float value){
card.setAlpha(value);
}
}
Declare your View Object globally in your fragment.
I have a fragment with a ViewPager inside it. In the ViewPager I have 4 content screens so swipe around in. The content has a few TextView components and I'm trying to access them from the first fragment, however when I go to use setText or similar I get a null pointer exception. Ive checked and the id for the TextView is valid, and I've done a clean build.
Here is a snippet of my relevant code:
private TextView textViewOne;
private PagerAdapter mPagerAdapter;
private ViewPager pager;
View rootView;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.fragment_layout_viewpager, container, false);
InitializePaging();
textViewOne = (TextView) rootView.findViewById(R.id.create_name);
//would return null if I did this:
textViewOne.setText("test");
return rootView;
}
private void InitializePaging() {
mPagerAdapter = new ViewPagerAdapter(getContext(), getChildFragmentManager(),
Arrays.asList(PageOne.class, PageTwo.class, PageThree.class, PageFour.class));
pager = (ViewPager) rootView.findViewById(R.id.content_pager);
pager.setAdapter(mPagerAdapter);
}
The PageOne class:
public class PageOne extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
if(container == null) {
return null;
}
return (LinearLayout) inflater.inflate(R.layout.fragment_page_one, container, false);
}
}
This is the fragment_layout_viewpager xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v4.view.ViewPager
android:id="#+id/content_pager"
android:layout_width="fill_parent"
android:layout_height="fill_parent"/>
</LinearLayout>
You are inflating fragment_layout_viewpager, so the create_name should exist in that layout, otherwise it will throw a null pointer.
Create an interface with 1 abstract method. Let the Fragment implement the interface and call the callback method from Activity.In the below example, I try to pass value on click of button from MainActivity to ThirdFragment.
public interface FragmentCommunicator {
public void passDataToFragment(String someValue);
}
public class MainActivity extends FragmentActivity {
FragmentCommunicator fragmentCommunicator;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Button btn= (Button)findViewById(R.id.button) ;
btnsetOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
randomvalue= getRansomString();
if(fragmentCommunicator!=null)
fragmentCommunicator.passDataToFragment(randomvalue);
}
});
ViewPager pager = (ViewPager) findViewById(R.id.viewPager);
pager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
}
private class MyPagerAdapter extends FragmentPagerAdapter {
public MyPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int pos) {
switch(pos) {
case 0: return FirstFragment.newInstance("FirstFragment, Instance 1");
case 1: return ThirdFragment.newInstance("ThirdFragment, Instance 1");
default: return FirstFragment.newInstance("FirstFragment,Instance 1");
}
}
#Override
public int getCount() {
return 2;
}
}
public static class FirstFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.first_frag, container, false);
TextView tv = (TextView) v.findViewById(R.id.tvFragFirst);
tv.setText(getArguments().getString("msg"));
return v;
}
public static FirstFragment newInstance(String text) {
Log.e("FirstFragment","newInstance called");
FirstFragment f = new FirstFragment();
Bundle b = new Bundle();
b.putString("msg", text);
f.setArguments(b);
return f;
}
}
public class ThirdFragment extends Fragment implements FragmentCommunicator {
TextView tv;
String value="";
public FragmentCommunicator fragmentCommunicator;
#Override
public void passDataToFragment(String someValue) {
this.value = someValue;
tv.setText(value);
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
((MainActivity)activity).fragmentCommunicator = this;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement FragmentCommunicator");
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.first_frag, container, false);
value=getArguments().getString("msg");
tv = (TextView) v.findViewById(R.id.tvFragFirst);
tv.setText(value);
return v;
}
public static ThirdFragment newInstance(String text) {
ThirdFragment f = new ThirdFragment();
Bundle b = new Bundle();
b.putString("msg",text);
f.setArguments(b);
return f;
}
}
I want to change the Fragment when i click the button. The fragments are in the same adapter/viewpager.
FROM THIS FRAGMENT:
public class LoginFragment extends Fragment {
TextView linkToRegister;
public static final LoginFragment newInstance()
{
LoginFragment mf = new LoginFragment();
Bundle bd = new Bundle(1);
mf.setArguments(bd);
return mf;
}
public View onCreateView(LayoutInflater inflater, final ViewGroup container, Bundle savedInstanceState )
{
View v = inflater.inflate(R.layout.fragment_login, container, false);
linkToRegister = (TextView) v.findViewById(R.id.link_to_register);
linkToRegister.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Change Fragment
}
});
return v;
}
}
TO THIS FRAGMENT:
public class RegisterFragment extends Fragment {
public static final String EXTRA_MESSAGE = "EXTRA_MESSAGE";
public static final RegisterFragment newInstance()
{
RegisterFragment mf = new RegisterFragment();
Bundle bd = new Bundle(1);
mf.setArguments(bd);
return mf;
}
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState )
{
View v = inflater.inflate(R.layout.fragment_register, container, false);
return v;
}
}
PagerAdapter:
public class WelcomePagerAdapter extends FragmentStatePagerAdapter {
private final List<Fragment> Welcomefragments;
public WelcomePagerAdapter(FragmentManager fm, List<Fragment> Welcomefragments) {
super(fm);
this.Welcomefragments = Welcomefragments;
}
#Override
public Fragment getItem(int position) {
return this.Welcomefragments.get(position);
}
#Override
public int getCount() {
return this.Welcomefragments.size();
}
}
Activity:
public class WelcomeActivity extends AppCompatActivity {
ViewPager welcomeViewPager;
WelcomePagerAdapter welcomePagerAdapter;
List<Fragment> welcomeFragments;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_welcome);
welcomeViewPager = (ViewPager) findViewById(R.id.viewPagerWelcome);
welcomeFragments = getWelcomeFragments();
welcomePagerAdapter = new WelcomePagerAdapter(getSupportFragmentManager(), welcomeFragments);
welcomeViewPager.setAdapter(welcomePagerAdapter);
}
public List<Fragment> getWelcomeFragments() {
List<Fragment> newFragment = new ArrayList<Fragment>();
newFragment.add(LoginFragment.newInstance());
newFragment.add(RegisterFragment.newInstance());
return newFragment;
}
}
Step 1: Define a callback interface in the Fragment and hook in the Activity when the Fragment attaches to it.
public class MyFragment extends Fragment {
public interface OnInteractionListener {
void doAction(); // Can include parameters here if needed
}
private OnInteractionListener listener;
#Override
public void onAttach(Context context) {
if (context instanceof OnInteractionListener) {
listener = (OnInteractionListener) context;
} else {
throw new ClassCastException(context + "must implement " + OnInteractionListener.class.getSimpleName());
}
super.onAttach(context);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_layout, container, false);
// ...
return v;
}
}
Step 2: Make sure your Activity implements that Interface
public class MyActivity extends AppCompatActivity implements MyFragment.OnInteractionListener {
#Override
public void doAction() {
// TODO: Implement this... e.g. switch fragments
}
...
}
Step 3: Inside the Fragment, you can invoke the callback whenever you want to perform some action
if (listener != null) {
listener.doAction();
}
From MainActivity(), get the navController and then use the navigate() function:
NavController navController = Navigation.findNavController(this,R.id.nav_host_fragment);
navController.navigate(R.id.nav_grid);
I have a viewpager with 2 pages, on each fragment i put a button to switching fragment,
but if i change orientation switching doesn't work.
For switching fragment I using my OnChangePageButtonClick interface
Why is this happening?
ViewPager Activity:
public class ViewPagerMusic extends FragmentActivity implements OnChangePageButtonClick {
private ViewPager vp;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.view_pager_music);
ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(super.getSupportFragmentManager(), fragments);
vp = (ViewPager)findViewById(R.id.viewpager);
vp.setAdapter(viewPagerAdapter);
}
private class ViewPagerAdapter extends FragmentStatePagerAdapter {
public ViewPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch(position) {
case 0:
MainPage mainPage = new MainPage();
mainPage.setOnChengeButtonListener(ViewPagerMusic.this);
return mainPage;
case 1:
PlaylistPage playlistPage = new PlaylistPage();
playlistPage.setOnChengeButtonListener(ViewPagerMusic.this);
return playlistPage;
}
return null;
}
#Override
public int getCount() {
return 2;
}
}
#Override
public void selectPage(int page) {
vp.setCurrentItem(page);
}
}
my Frgamnets:
public class MainPage extends Fragment {
public MainPage() {
setRetainInstance(true);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.music_main_page, container, false);
ImageButton btnPlaylist = (ImageButton)v.findViewById(R.id.btnGoPlaylist2);
btnPlaylist.setOnClickListener(onButtonListener);
return v;
}
private OnClickListener onButtonListener = new OnClickListener() {
#Override
public void onClick(View view) {
onChangePageButtonClick.selectPage(1);
}
};
public void setOnBackButtonListener(OnChangePageButtonClick onChangePageButtonClick) {
this.onChangePageButtonClick = onChangePageButtonClick;
}
private OnChangePageButtonClick onChangePageButtonClick;
}
Playlist fragment is similar to MainPage fragment.
Your fragments are storing a reference to the ViewPagerMusic activity. However, after rotation, the activity is destroyed and recreated, so the fragments now contain a reference to the old activity.
Instead of storing a reference to the activity, you can call the activity's method from the fragment like this:
((ViewPagerMusic) getActivity()).selectPage(1);
just create this method in your view pager
#Override
public void selectPage(int page) {
vp.setCurrentItem(page);
}
and then call this in your onclick method
((ViewPagerMusic) getActivity()).selectPage(1);