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Open fragment from a fragment with cardview

How can I open a fragment from a fragment with Cardview? I have a list of Cardview in fragment_home.xml and when i click in one of those want to show in another fragment.
Here is what i have so far.
fragment_home.xml
<androidx.cardview.widget.CardView
android:id="#+id/cvCocktails"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="10dp"
app:cardCornerRadius="15dp"
app:cardElevation="0dp"
app:layout_columnWeight="1"
app:layout_rowWeight="1"
>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:onClick="Cocktails">
<ImageView
android:id="#+id/ivCocktails"
android:layout_width="115dp"
android:layout_height="115dp"
android:layout_centerInParent="true"
android:contentDescription="#string/cocktail"
android:src="#drawable/cocktail_color"
android:translationY="-15dp"
tools:ignore="VisualLintBounds" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#id/ivCocktails"
android:layout_centerHorizontal="true"
android:text="#string/cocktail"
android:textSize="20dp"
tools:ignore="SpUsage,TextSizeCheck" />
</RelativeLayout>
HomeFragment.java
public class HomeFragment extends Fragment {
public CardView cocktails;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_home,container,false);
cocktails = view.findViewById(R.id.cvCocktails);
cocktails.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
CocktailFragment cocktailFragment = new CocktailFragment();
getActivity().getSupportFragmentManager().beginTransaction()
.replace(R.id.fragment_home,cocktailFragment,null)
.addToBackStack(null).commit();
}
});
return view;
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
}
}
When i compile the app and click on Cocktail Cardview i have this error. How can i fix this. Thank you.
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.barapp, PID: 11805
java.lang.IllegalStateException: Could not find method Cocktails(View) in a parent
or ancestor Context for android:onClick attribute defined on view class
android.widget.RelativeLayout
at android.view.View$DeclaredOnClickListener.resolveMethod(View.java:6302)
at android.view.View$DeclaredOnClickListener.onClick(View.java:6259)
at android.view.View.performClick(View.java:7448)
at android.view.View.performClickInternal(View.java:7425)
at android.view.View.access$3600(View.java:810)
at android.view.View$PerformClick.run(View.java:28305)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

Fragment in viewpager2: Android app crashes when resuming after being killed by OS

My Android app crashes when resuming after being killed by OS due to low memory.
So I have built the smallest possible app to reproduce the bug.
My app is composed of a MainActivity, which contains 1 page in a viewPager2, which contains a fragment.
This fragment is added dynamically by replacing "structure_placeholder" (in the real app, the type of fragment depends on some parameters)
MainActivity.java:
public class MainActivity extends AppCompatActivity
{
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(this);
ViewPager2 viewPage = findViewById(R.id.viewpager);
viewPage.setAdapter(sectionsPagerAdapter);
}
/***************************************************************************/
class SectionsPagerAdapter extends FragmentStateAdapter
{
private SectionsPagerAdapter(FragmentActivity fa)
{
super(fa);
}
#NonNull #Override
public Fragment createFragment(int position)
{
return new MyPageFragment();
}
#Override
public int getItemCount()
{
return 1;
}
}
}
activity_main.xml:
<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"
tools:context=".MainActivity">
<androidx.viewpager2.widget.ViewPager2
android:id="#+id/viewpager"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
MyPageFragment.java:
public class MyPageFragment extends Fragment
{
public MyPageFragment()
{ /* Required empty public constructor*/}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
return inflater.inflate(R.layout.my_page_fragment, container, false);
}
#Override
public void onStart()
{
super.onStart();
Fragment listFragment = SubFragment.newInstance();
FragmentTransaction ft = requireActivity().getSupportFragmentManager().beginTransaction();
ft.replace(R.id.structure_placeholder, listFragment);
ft.commit();
}
}
my_page_fragment.xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
tools:context=".MyPageFragment">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_blank_fragment" />
<FrameLayout
android:id="#+id/structure_placeholder"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
tools:layout_width="100dp"
tools:layout_height="150dp"
tools:background="#color/design_default_color_secondary"
>
</FrameLayout>
</LinearLayout>
SubFragment.java:
public class SubFragment extends Fragment
{
public SubFragment()
{ /* Required empty public constructor*/ }
public static SubFragment newInstance()
{
SubFragment fragment = new SubFragment();
Bundle args = new Bundle();
fragment.setArguments(args);
return fragment;
}
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
return inflater.inflate(R.layout.sub_fragment, container, false);
}
}
sub_fragment.xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/line1" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/line2" />
</LinearLayout>
Here is the error log when resuming the app after it has been killed:
2021-11-19 15:46:55.739 8298-8298/com.delrocq.mytestapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.delrocq.mytestapp, PID: 8298
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.delrocq.mytestapp/com.delrocq.mytestapp.MainActivity}: java.lang.IllegalArgumentException: No view found for id 0x7f0801db (com.delrocq.mytestapp:id/structure_placeholder) for fragment SubFragment{9eb5496} (ada1c808-c885-49ed-9cd3-f4de1855c6af id=0x7f0801db)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2957)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6944)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
Caused by: java.lang.IllegalArgumentException: No view found for id 0x7f0801db (com.delrocq.mytestapp:id/structure_placeholder) for fragment SubFragment{9eb5496} (ada1c808-c885-49ed-9cd3-f4de1855c6af id=0x7f0801db)
I tried to put some logs to understand the lifecycle of the activity/fragments, but it did not help.
What am I doing wrong?

I finally found the solution after hours of searching and many wrong tracks.
Inside a fragment, getChildFragmentManager() shall be used instead of getSupportFragmentManager().
It is so easy when you know it :)

Could not find method butonCap(View) in a parent or ancestor

I've been searching the error for about 2 hours on google , i can't figure out what it's wrong . It just force closes when I tap the button "butonCap", I didn't work with fragments until now
ERROR:
java.lang.IllegalStateException: Could not find method butonCap(View) in a parent or ancestor Context for android:onClick attribute defined on view class android.support.v7.widget.AppCompatButton with id 'cap'
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.resolveMethod(AppCompatViewInflater.java:423)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:380)
at android.view.View.performClick(View.java:6897)
at android.widget.TextView.performClick(TextView.java:12693)
at android.view.View$PerformClick.run(View.java:26101)
at android.os.Handler.handleCallback(Handler.java:789)
at android.os.Handler.dispatchMessage(Handler.java:98)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6944)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
Butoane.java - i just made another java file because i can't write any code in the fragment java file
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_fata);
final Button butonCap = (Button) findViewById(R.id.cap);
butonCap.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent butonCap = new Intent(Butoanele.this, capul.class);
Butoanele.this.startActivity(butonCap);
}
});
}
}
fragment_fata.xml - this is just one of the 2 fragments from navigation view
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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=".FragmentFata"
android:background="#drawable/fata">
<!-- TODO: Update blank fragment layout -->
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="#+id/cap"
android:layout_width="wrap_content"
android:layout_height="65dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="4dp"
android:background="#drawable/button_outline"
android:paddingBottom="30dp"
android:onClick="butonCap"
android:text="Cap"
android:textSize="18sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
/>

You class should extends Fragment and inflate layout in onCreateView() callback.
Call getActivity().findViewById in onViewCreated() callback.
watch this guide

In fragment:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
//Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_fata, container, false);
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
if (getView() == null) {
return;
}
final Button butonCap = (Button) getView().findViewById(R.id.cap);
butonCap.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent intent = new Intent(getView().getContext(), capul.class);
startActivity(intent);
}
});
}

How to link and image to another xml layout?

I am new to android and is in need for some little help.I have a xml layout called fragment_home.xml which contains some images.I want to redirect the user to another page(fragment_about_sl.xml) when the user clicks on an image.Please tell me how to do that and where to place the codes.
fragment_home.xml(layout with the images)
<LinearLayout
android:id="#+id/home"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
tools:context="com.example.sloid.destinations.navigationdrawerfragments.homeFragment"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:gravity="center_horizontal">
<ImageView
android:id="#+id/aboutslbtn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:layout_marginTop="10dp"
android:layout_marginBottom="10dp"
android:src="#drawable/aboutsl"
/>
<ImageView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:layout_marginBottom="10dp"
android:src="#drawable/toplandmarks"
/>
</LinearLayout>
</ScrollView>
</LinearLayout>
fragment_about_sl.xml(the layout that should be redirected once image is clicked)
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/aboutslscrollview"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.sloid.destinations.navigationdrawerfragments.aboutSLFragment">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.v4.view.ViewPager
android:id="#+id/viewPager"
android:layout_width="match_parent"
android:layout_height="250dp" />
<LinearLayout
android:id="#+id/SliderDots"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignBottom="#id/viewPager"
android:layout_marginBottom="20dp"
android:gravity="center_horizontal"
android:orientation="horizontal" />
</RelativeLayout>
</LinearLayout>
</ScrollView>
I also added the java file if its necessary.
homeFragment.java(java file for fragment_home.xml)
public class homeFragment extends Fragment {
public homeFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_home, container, false);
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
//you can set the title for your toolbar here for different fragments different titles
getActivity().setTitle("Destinations");
}
}
aboutSLFragment.java(java file for fragment_about_sl.xml)
public class aboutSLFragment extends Fragment{
ViewPager viewPager;
LinearLayout sliderDotspanel;
private int dotscount;
private ImageView[] dots;
TextView aboutsltext;
Button readmorebtn;
public aboutSLFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_about_sl, container, false);
viewPager = (ViewPager) rootView .findViewById(R.id.viewPager);
sliderDotspanel = (LinearLayout)rootView.findViewById(R.id.SliderDots);
ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(getContext());
viewPager.setAdapter(viewPagerAdapter);
dotscount = viewPagerAdapter.getCount();
dots = new ImageView[dotscount];
for(int i = 0; i < dotscount; i++){
dots[i] = new ImageView(getContext());
dots[i].setImageDrawable(ContextCompat.getDrawable(getContext(), R.drawable.non_active_dot));
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
params.setMargins(8, 0, 8, 0);
sliderDotspanel.addView(dots[i], params);
}
dots[0].setImageDrawable(ContextCompat.getDrawable(getContext(), R.drawable.active_dot));
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
for(int i = 0; i< dotscount; i++){
dots[i].setImageDrawable(ContextCompat.getDrawable(getContext(), R.drawable.non_active_dot));
}
dots[position].setImageDrawable(ContextCompat.getDrawable(getContext(), R.drawable.active_dot));
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
aboutsltext=(TextView)rootView.findViewById(R.id.aboutsltext);
readmorebtn=(Button)rootView.findViewById(R.id.readmorebtn);
readmorebtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (readmorebtn.getText().toString().equalsIgnoreCase("Read More"))
{
aboutsltext.setMaxLines(Integer.MAX_VALUE);//your TextView
readmorebtn.setText("Read Less");
}
else
{
aboutsltext.setMaxLines(3);//your TextView
readmorebtn.setText("Read More");
}
}
});
// Inflate the layout for this fragment
return rootView;
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
//you can set the title for your toolbar here for different fragments different titles
getActivity().setTitle("About Sri Lanka");
}
code added to change the fragment
rootView.findViewById(R.id.aboutslbtn).setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Fragment fragment = new aboutSLFragment();
FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.home, fragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
}
});
logcat
30388-30388/com.example.sloid.destinations E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.sloid.destinations, PID: 30388
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sloid.destinations/com.example.sloid.destinations.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2702)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2767)
at android.app.ActivityThread.access$900(ActivityThread.java:177)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5951)
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:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at com.example.sloid.destinations.navigationdrawerfragments.homeFragment.onCreateView(homeFragment.java:30)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2354)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1419)
at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1740)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1809)
at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:799)
at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2580)
at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2367)
at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2322)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2229)
at android.support.v4.app.FragmentManagerImpl.dispatchStateChange(FragmentManager.java:3221)
at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:3171)
at android.support.v4.app.FragmentController.dispatchActivityCreated(FragmentController.java:192)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:560)
at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:177)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1234)
at android.app.Activity.performStart(Activity.java:6329)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2767) 
at android.app.ActivityThread.access$900(ActivityThread.java:177) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:145) 
at android.app.ActivityThread.main(ActivityThread.java:5951) 
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:1399) 

Just add ids to those images and handle onclick events inside your fragment. You can find the image view using findViewById(R.id.'yourId');
And the onClick listener set: view.setOnClickListener(...);

As per My comment
Reference : Fragment replace
Fragment fragment = new aboutSLFragment();
FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.home, fragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
Tutorial : https://www.javacodegeeks.com/2013/06/android-fragment-transaction-fragmentmanager-and-backstack.html

You are new in android right, first of all you need to check Fragment detail
As you question you need to replace or add fragment as #Vishva Dave said
Follow this link
private void loadFragment(Fragment fragment) {
// create a FragmentManager
FragmentManager fm = getFragmentManager();
// create a FragmentTransaction to begin the transaction and replace the Fragment
FragmentTransaction fragmentTransaction = fm.beginTransaction();
// replace the FrameLayout with new Fragment
fragmentTransaction.replace(R.id.frameLayout, fragment);
fragmentTransaction.commit(); // save the changes
}

First you need to add android:id="#+id/imageId" to the <ImageView ... in the xml, then in your homefragment add this code:
public class homeFragment extends Fragment {
View rootView;
public homeFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
rootView = inflater.inflate(R.layout.fragment_home, container, false);
rootView.findViewById(R.id.imageId).setOnClickListener(new OnClickListener(){
// go to the other fragment using fragmentTransaction
});
return rootView;
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
//you can set the title for your toolbar here for different fragments
different titles
getActivity().setTitle("Destinations");
}
}

NullPointerException with onClickListener for elements in Fragment

I'm having a hell of a time getting fragments to work. The basis of this is to lave a login screen (fragment) appear by default when LoginActivity is created. The fragment has an TextView that when clicked, is supposed to launch a new fragment (form for lost password). I keep getting a NullPointerException when calling forgottenPassword.setOnClickListener from LoginActivity.
The project crashes before I can tell if anything else works.
I'm sure there's some glaring newbie error in here somewhere...
onCreate method from LoginActivity.java:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
if (savedInstanceState == null) {
FragmentManager fragmentManager = getFragmentManager();
int fragmentTransaction = fragmentManager.beginTransaction()
.add(R.id.login_screen_fragment, new FragmentLogin())
.commit();
}
// Listen for FORGOTTEN PASSWORD click event, open ForgottenPassword Fragment //
final TextView forgottenPassword = (TextView) findViewById(R.id.button_lost_pass);
forgottenPassword.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Do what I need this to do...
}
});
}
layout_login.xml:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/login_screen_fragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".LoginActivity"
/>
fragment_login:
<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"
tools:context="come.xxxx.xxxx.ForgottenPasswordFragment">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
>
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="#string/login_email"
android:id="#+id/login_forgot"
/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:text="#string/login_send_lost_pass"
android:id="#+id/button_lost_pass"
/>
</LinearLayout>
</FrameLayout>
fragment_lost_password.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"
tools:context="com.xxxx.xxx.FragmentLogin">
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:fitsSystemWindows="true">
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="20dp"
android:orientation="vertical"
android:layout_gravity="center"
android:focusable="true"
android:focusableInTouchMode="true">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="I forgot my password"
android:gravity="center"
android:layout_marginTop="32dp"
android:padding="8dp"
android:textSize="16sp"
android:id="#+id/login_forgot"
/>
</LinearLayout>
</ScrollView>
</FrameLayout>
FragmentLogin.java:
public class FragmentLogin extends Fragment {
public FragmentLogin() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
final View view = inflater.inflate(R.layout.fragment_login, container, false);
return view;
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
final Activity activity = getActivity();
}
}
FragmentLostPassword.java
public class FragmentForgottenPassword extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_forgotten_password, container, false);
}
}
Error Trace:
05-13 12:49:37.222 15163-15163/com.xxxxx.xxxxx E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.xxxxx.xxxxx, PID: 15163
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.xxxxx.xxxxx/com.xxxxx.xxxxx.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.xxxxx.xxxxx.LoginActivity.onCreate(LoginActivity.java:51)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
at android.app.ActivityThread.access$800(ActivityThread.java:151) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:135) 
at android.app.ActivityThread.main(ActivityThread.java:5254) 
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:903) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
05-13 12:50:28.592 15163-15173/com.xxxxx.xxxxx W/art: Suspending all threads took: 15.077ms
05-13 12:50:44.622 15163-15163/? I/Process: Sending signal. PID: 15163 SIG: 9

You have to find the View in your Fragment's layout.
Use the following in your FragmentLogin class:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
final View view = inflater.inflate(R.layout.fragment_login, container, false);
final TextView forgottenPassword = (TextView) view.findViewById(R.id.button_lost_pass);
// Set your onClickListener here
return view;
}

Actually, your fragment might be not accessible when you assign forgetpassword , you can use the following for layout_login.xml:
<fragment
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/main_container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:name="FragmentLogin"
tools:layout="#layout/fragment_login"
/>
Note you may have to define the right path to FragmentLogin.
This is the new way to work with fragment, that will load your Login fragment automatically without writing anything in onCreate.
Also, it's not a TextView but a Button
Finally, remove the Fragment Transaction code.
Another option, is to move your forgot password button login to FragmentLogin. Because basically you try to access Fragment related element from the activity. Everything should be in your fragment.
You can still access the fragment manager with getActivity().getFragmentManger(), to load the lost_password layout.

What is the activity_login.xml content. I guest wrong id of button button_lost_pass

Inside oncreate() method you called new Fragment but the fragment layout(layout_lost_password) does not contain the id(R.id.button_lost_pass)

Change :
final TextView forgottenPassword = (TextView) findViewById(R.id.button_lost_pass);
To
final Button forgottenPassword = (Button) findViewById(R.id.button_lost_pass);