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why the app crashes when I use onclicklistener with Fragment?

public class MainActivity extends AppCompatActivity {
Context context;
LinearLayout menuClcick,gallerClcik,eventsClick;
LayoutInflater inflater;`enter code here`
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//we don't need to set view, our fragment will handle it
setPointer();
//Fragment Manger
FragmentManager fm = getFragmentManager();
//create instance of Fragment Transaction to handle fragment replace and animation
FragmentTransaction ft=fm.beginTransaction();
int displayMode = getResources().getConfiguration().orientation;
Log.e("WTF", "onCreate: "+displayMode );
//choose which fragment to display according to screen orientation
if (displayMode==1) //portrait
{
// that's the Fragment that I use to display a layout in the portrait and other layout in the landscape//
//create instance of our portrait fragment
Fragment1 f1=new Fragment1();
//change content of the screen to our new fragment
ft.replace(android.R.id.content,f1);
}
else
{
Fragment2 f2=new Fragment2();
ft.replace(android.R.id.content,f2);
}
//choose animation
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
//commit our changes
ft.commit();
}
private void setPointer() {
this.context=this;
menuClcick=findViewById(R.id.menuClick);
gallerClcik=findViewById(R.id.gallerClcik);
eventsClick=findViewById(R.id.eventsClick);
//this is the problem the app have no problem to find the buttons but it stops working when I try to put onclick listener in it//
menuClcick.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(context, "portrait", Toast.LENGTH_SHORT).show();
}
});
}

You are trying to access views that are not yet created,
As the documentation lifecycle shows, you should implement onCreateView() to inflate your layout and only there you have access to your R.id.menuClick.
So basically, you should call your setPointer() method on onCreateView().

fragment reference null on resume

Im having an issue that only appears after several hours of inactivity, I researched it ive tried various ways of fixing it to no avail. The issue is after my app has been dormant for several hours the references for my fragments are null, however; they still exist in the frag manager. I use the references to pull the tag, or id by findfragmentby...() so I can call specific methods within them for updating themselves and what not. The fragments are dynamic and have a UI. I have several activities and a service that are called on by the main activity. I can close the app and resume, call activities, pull info from the service, close, use the back button, all without an issue. To give you an idea of how the app is structured...
public class appClass extends Application {
public Fragment fragmentA;
public Fragment fragmentB;
public Fragment fragmentC;
#Override
public void onCreate() {
super.onCreate();
new fragmentTemplate();
fragemntA = fragmentTemplate.newInstance(getDbName(), usefuldata, "A List");
new fragmentTemplate();
fragemntB = fragmentTemplate.newInstance(getDbName(), usefuldata, "B list");
new fragmentTemplate();
fragemntC = fragmentTemplate.newInstance(getDbName(), usefuldata, "C list");
}
}
Moving on to activity where fragments are used in a viewager...
public class mainActivity extends AppCompatActivity implements ...listeners{
appClass myAppClass;
FragmentManager FragMgr;
ViewPager viewPager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
myAppClass = (appClass) getApplication();
setTheme(myAppClass.getAppTheme());
setContentView(R.layout.activity_my_layout);
//toolbar actionbar stuff
FragMgr = getSupportFragmentManager();
viewPager = (ViewPager) findViewById(R.id.viewpager);
viewPager.setAdapter(new ViewPagerAdapter(FragMgr));
//tab setup
}
//inner class pager adapter is here
}
This is my pager adapter
class ViewPagerAdapter extends FragmentPagerAdapter implements ViewPager.OnPageChangeListener{
Fragment fragment;
public ViewPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
if (myAppClass.fragmentA != null) {
fragment = myAppClass.fragemntA ;
}
break;
case 1:
if (myAppClass.fragmentB != null) {
fragment = myAppClass.fragmentB ;
}
break;
case 2:
if (myAppClass.fragmentC != null) {
fragment = myAppClass.fragmentC ;
}
break;
}
return fragment;
}
#Override
public int getCount() {
return 3;
}
}
I have a FAB and its listener looks like this
#Override
public void onClick(View v) {
Fraggment fragment;
int i = viewPager.getCurrentItem();
if (v.getId() == floatingActionButton.getId()) {
switch (i) {
case 0:
fragment= (Fragment) FragMgr.findFragmentByTag(myAppClass.fragmentA.getTag());
fragment.addItem(fragment.getSomeString());
break;
case 1:
fragment= (Fragment) FragMgr.findFragmentByTag(myAppClass.fragmentB.getTag());
fragment.addItem(fragment.getSomeString());
break;
case 2:
fragment= (Fragment) FragMgr.findFragmentByTag(myAppClass.fragmentC.getTag());
fragment.addItem(fragment.getSomeString());
break;
}
}
}
code for a fragment
public class fragmentTemplate extends Fragment implements RecyclerAdapter.aListener {
private appClass myAppclassReference;
private RecyclerView recyclerView;
private View view;
private FragmentTitle;
public static fragmentTemplate newInstance(String a, String b, String c) {
Bundle args = new Bundle();
args.putString(KEY_A, a);
args.putString(KEY_B, b);
args.putString(KEY_C, c);
fragmentTemplate fragment = new fragmentTemplate();
fragment.setArguments(args);
return fragment;
}
public String getFragmentTitle() {
return fragmentTitle;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, final Bundle savedInstanceState) {
view = inflater.inflate(R.layout.list, container, false);
myAppclassReference= ((appClass) getActivity().getApplication());
recyclerView = (RecyclerView) view.findViewById(R.id.listView);
//get list is a local function that loads a list from a db source
RecyclerAdapter recycler = new RecyclerAdapter(getActivity(), getList());
recycler.setListener(this);
recyclerView.setAdapter(recycler);
recyclerView.setLayoutManager(newLearLayoutManager(getActivity()));
recyclerView.addOnItemTouchListener(new RecyclerTouchListener(getActivity(), recyclerView, new ClickListener() {}};
return view;
}
}
When things go wonky the app does not crash right away, the tabs still scroll, the viewpager still scrolls, but it is empty, its not until I hit the FAB do I get a nullpointerexception, trying to invoke a method on a nullpointer reference within the onClick Listener does it actually crash.

This is happening because you are messing up with the way that the Android Framework handles Fragments for you. When the ViewPagerAdapter gets Fragments from you in getItem(int), it's using the FragmentManager that you gave it to attach the Fragments. Once the Activity is killed because of low memory, the FragmentManager will automatically create new instances of your Fragments. At this point there are two copies of the fragments, the ones the FragmentManager created and the ones you recreated in your appClass.
You should never keep references to your Fragments. The FragmentManager is free to destroy them and create new ones. If you need to communicate between the Activity and the Fragments in the ViewPager, you can either make the Fragment ask its Activity for commands, use an Event Bus, or explore the sketchy solutions here.

Android oncreateview called twice

I have see this question asked here more than one time but I can't figure it out how to solve for my case.
I have an app that the user does this:
1 - Open the navigationDrawer and selects one option (a fragment is created) (I'm here selecting the second option);
public void selectItem(int position) {
Fragment fragment = null;
switch (position) {
case FRAGMENT_OPTION1:
...
break;
case FRAGMENT_OPTION2:
fragment = ControlPanelFragment.newInstance();
break;
...
case FRAGMENT_OPTIONN:
...
return;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.fragment_container, fragment).commitAllowingStateLoss();
}
}
2 - The selected option (ControlPanelFragment) gets loaded:
2.1 - Control panel has tabs and an iconpager. For each pager page and for each tab a new fragment is created. I have 3 tabs and 3 pages so 9 fragments are created;
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
if (savedInstanceState != null) {
currentControlPanelOption = savedInstanceState.getInt("currentControlPanelOption", currentControlPanelOption);
currentControlPanelTab = savedInstanceState.getInt("currentControlPanelTab", currentControlPanelTab);
}
setControlPanelTabs();
setIconPager();
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("currentControlPanelOption", pager.getCurrentItem());
outState.putInt("currentControlPanelTab", mTabHost.getCurrentTab());
}
3 - In the setIconPager(); I have this code:
pager = (ViewPager) view.findViewById(R.id.pager);
cPanelPagerAdapter = new ControlPanelPagerAdapter(getChildFragmentManager());
pager.setOffscreenPageLimit(2);
pager.setAdapter(cPanelPagerAdapter);
where ControlPanelPagerAdapter has this code:
public Fragment getItem(int index) {
Fragment fragment;
switch (index) {
case 1:
fragment = FragmentA.newInstance();
break;
case 2:
fragment = FragmentB.newInstance();
break;
case 3:
fragment = FragmentC.newInstance();
break;
default:
fragment = null;
break;
}
...
return fragment;
}
4 - FragmentA, FragmentB and FragmentC have almost the same code:
public static FragmentA newInstance() {
return new FragmentA();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_placeholder, container, false);
return view;
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
if (savedInstanceState == null) {
fragmentA_Data = new FragmentADetail[3];
createTabInstance(0);
} else {
fragmentA_Data = (FragmentADetail[]) savedInstanceState.getSerializable("Data");
return;
}
}
private void createTabInstance(int tab) {
new FragmentADetail();
fragment = FragmentADetail.newInstance(tab);
Bundle args = new Bundle();
args.putInt("tab", tab);
fragment.setArguments(args);
fragmentA_Data[tab] = fragment;
FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_placeholder, fragmentA_Data[tab]);
fragmentTransaction.commitAllowingStateLoss();
}
public void getTabData(int tab) {
if (fragmentA_Data[tab] == null) {
createStoreTimePeriodInstance(tab);
} else {
if (fragmentA_Data[tab].getArguments() == null) {
Bundle args = new Bundle();
args.putInt("tab", tab);
fragmentA_Data[tab].setArguments(args);
}
FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_placeholder, fragmentA_Data[tab]);
fragmentTransaction.commitAllowingStateLoss();
}
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putSerializable("data", fragmentA_Data);
}
5 - Finally, FragmentADetail has this code:
public static FragmentADetail newInstance(int tab) {
selectedTab = tab;
return new FragmentADetail();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
view = inflater.inflate(R.layout.details_fragment, container, false);
...
if (savedInstanceState != null) {
selectedTab = savedInstanceState.getInt("selectedTab");
}
...
}
public void getTabData(int tab) {
//This is where I'm getting the data that populates the layout
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("selectedTab", selectedTab);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
Bundle args = getArguments();
if (args != null) {
getTabData(args.getInt("tab"));
}
}
Now, imagine I'm on FragmentA with the third tab selected. If I rotate the screen I have this sequence of events:
ControlPanelFragment onSaveInstanceState saves the current tab and current fragment
FragmentA onSaveInstanceState saves the tabs fragments for the pager
navigationDrawer second option gets again called fragment = ControlPanelFragment.newInstance();
ControlPanelFragment onViewCreated is called and I can get the saved data information and a new pager and tabs are created
FragmentA onViewCreated is called and I can extract the saved data
FragmentADetail onActivityCreated gets the saved data and loads the data correctelly (at least I think)
And from now a second set of methods is called the second time and the data that was previously saved is reseted and so it now displays wrong data
ControlPanelFragment onSaveInstanceState but now the savedInstanceState is null
ControlPanelPagerAdapter getItem is called instantiating the 3 fragments
FragmentA onSaveInstanceState its now called but savedInstanceState is null
FragmentADetail onActivityCreated is called but now the tab = 0
Can someone explain-me how can I stop steps 7 to 10 from happening?

I figure out what was my problem.
When I was doing:
case FRAGMENT_OPTION2:
fragment = ControlPanelFragment.newInstance();
break;
I was creating a fragment and when I rotated the screen selectItem(int position) was again called so a new instance of the same object was created thus the steps 7 and following. The solution was to check if the fragment was already created and use him instead of creating a new one.
I've saved the initial fragment with a tag and them looked for that tag. If the tag existed, use that fragment otherwise create a new one.
public void selectItem(int position) {
Fragment fragment = null;
switch (position) {
case FRAGMENT_OPTION1:
...
break;
case FRAGMENT_OPTION2:
fragment = getSupportFragmentManager().findFragmentByTag(String.valueOf(position));
if (fragment == null) {
fragment = ControlPanelFragment.newInstance();
}
break;
...
case FRAGMENT_OPTIONN:
...
return;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.fragment_container, fragment,
String.valueOf(position)).commitAllowingStateLoss();
}
}

Android - save/restore fragment state

I have an Activity in which I go through several fragments. In every fragment I have several views (EditText, ListView, Map, etc).
How can I save the instance of the fragment that is shown at that moment? I need it to work when the activity is onPause() --> onResume(). Also I need it to work when I return from another fragment (pop from backstack).
From the main Activity I call the first fragment, then from the the fragment I call the next one.
Code for my Activity:
public class Activity_Main extends FragmentActivity{
public static Fragment_1 fragment_1;
public static Fragment_2 fragment_2;
public static Fragment_3 fragment_3;
public static FragmentManager fragmentManager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
fragment_1 = new Fragment_1();
fragment_2 = new Fragment_2();
fragment_3 = new Fragment_3();
fragmentManager = getSupportFragmentManager();
FragmentTransaction transaction_1 = fragmentManager.beginTransaction();
transaction_1.replace(R.id.content_frame, fragment_1);
transaction_1.commit();
}}
Then here is the code for one of my fragments:
public class Fragment_1 extends Fragment {
private EditText title;
private Button go_next;
#Override
public View onCreateView(final LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_1,
container, false);
title = (EditText) rootView.findViewById(R.id.title);
go_next = (Button) rootView.findViewById(R.id.go_next);
image.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
FragmentTransaction transaction_2 = Activity_Main.fragmentManager
.beginTransaction();
transaction_2.replace(R.id.content_frame,
Activity_Main.fragment_2);
transaction_2.addToBackStack(null);
transaction_2.commit();
});
}}
I have searched a lot of information but nothing clear. Can somebody give a clear solution and an example, please ?

When a fragment is moved to the backstack, it isn't destroyed. All the instance variables remain there. So this is the place to save your data. In onActivityCreated you check the following conditions:
Is the bundle != null? If yes, that's where the data is saved (probably orientation change).
Is there data saved in instance variables? If yes, restore your state from them (or maybe do nothing, because everything is as it should be).
Otherwise your fragment is shown for the first time, create everything anew.
Edit: Here's an example
public class ExampleFragment extends Fragment {
private List<String> myData;
#Override
public void onSaveInstanceState(final Bundle outState) {
super.onSaveInstanceState(outState);
outState.putSerializable("list", (Serializable) myData);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
if (savedInstanceState != null) {
//probably orientation change
myData = (List<String>) savedInstanceState.getSerializable("list");
} else {
if (myData != null) {
//returning from backstack, data is fine, do nothing
} else {
//newly created, compute data
myData = computeData();
}
}
}
}

Android fragment has some advantages and some disadvantages.
The most disadvantage of the fragment is that when you want to use a fragment you create it ones.
When you use it, onCreateView of the fragment is called for each time. If you want to keep state of the components in the fragment you must save fragment state and yout must load its state in the next shown.
This make fragment view a bit slow and weird.
I have found a solution and I have used this solution: "Everything is great. Every body can try".
When first time onCreateView is being run, create view as a global variable. When second time you call this fragment onCreateView is called again you can return this global view. The fragment component state will be kept.
View view;
#Override
public View onCreateView(LayoutInflater inflater,
#Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
setActionBar(null);
if (view != null) {
if ((ViewGroup)view.getParent() != null)
((ViewGroup)view.getParent()).removeView(view);
return view;
}
view = inflater.inflate(R.layout.mylayout, container, false);
}

Try this :
#Override
protected void onPause() {
super.onPause();
if (getSupportFragmentManager().findFragmentByTag("MyFragment") != null)
getSupportFragmentManager().findFragmentByTag("MyFragment").setRetainInstance(true);
}
#Override
protected void onResume() {
super.onResume();
if (getSupportFragmentManager().findFragmentByTag("MyFragment") != null)
getSupportFragmentManager().findFragmentByTag("MyFragment").getRetainInstance();
}
Hope this will help.
Also you can write this to activity tag in menifest file :
android:configChanges="orientation|screenSize"
Good luck !!!

In order to save the Fragment state you need to implement onSaveInstanceState():
"Also like an activity, you can retain the state of a fragment using a Bundle, in case the activity's process is killed and you need to restore the fragment state when the activity is recreated. You can save the state during the fragment's onSaveInstanceState() callback and restore it during either onCreate(), onCreateView(), or onActivityCreated(). For more information about saving state, see the Activities document."
http://developer.android.com/guide/components/fragments.html#Lifecycle

As stated here: Why use Fragment#setRetainInstance(boolean)?
you can also use fragments method setRetainInstance(true) like this:
public class MyFragment extends Fragment {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// keep the fragment and all its data across screen rotation
setRetainInstance(true);
}
}

You can get current Fragment from fragmentManager. And if there are non of them in fragment manager you can create Fragment_1
public class MainActivity extends FragmentActivity {
public static Fragment_1 fragment_1;
public static Fragment_2 fragment_2;
public static Fragment_3 fragment_3;
public static FragmentManager fragmentManager;
#Override
protected void onCreate(Bundle arg0) {
super.onCreate(arg0);
setContentView(R.layout.main);
fragment_1 = (Fragment_1) fragmentManager.findFragmentByTag("fragment1");
fragment_2 =(Fragment_2) fragmentManager.findFragmentByTag("fragment2");
fragment_3 = (Fragment_3) fragmentManager.findFragmentByTag("fragment3");
if(fragment_1==null && fragment_2==null && fragment_3==null){
fragment_1 = new Fragment_1();
fragmentManager.beginTransaction().replace(R.id.content_frame, fragment_1, "fragment1").commit();
}
}
}
also you can use setRetainInstance to true what it will do it ignore onDestroy() method in fragment and your application going to back ground and os kill your application to allocate more memory you will need to save all data you need in onSaveInstanceState bundle
public class Fragment_1 extends Fragment {
private EditText title;
private Button go_next;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true); //Will ignore onDestroy Method (Nested Fragments no need this if parent have it)
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
onRestoreInstanceStae(savedInstanceState);
return super.onCreateView(inflater, container, savedInstanceState);
}
//Here you can restore saved data in onSaveInstanceState Bundle
private void onRestoreInstanceState(Bundle savedInstanceState){
if(savedInstanceState!=null){
String SomeText = savedInstanceState.getString("title");
}
}
//Here you Save your data
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putString("title", "Some Text");
}
}

I'm not quite sure if this question is still bothering you, since it has been several months. But I would like to share how I dealt with this.
Here is the source code:
int FLAG = 0;
private View rootView;
private LinearLayout parentView;
/**
* The fragment argument representing the section number for this fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section number.
*/
public static Fragment2 newInstance(Bundle bundle) {
Fragment2 fragment = new Fragment2();
Bundle args = bundle;
fragment.setArguments(args);
return fragment;
}
public Fragment2() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
Log.e("onCreateView","onCreateView");
if(FLAG!=12321){
rootView = inflater.inflate(R.layout.fragment_create_new_album, container, false);
changeFLAG(12321);
}
parentView=new LinearLayout(getActivity());
parentView.addView(rootView);
return parentView;
}
/* (non-Javadoc)
* #see android.support.v4.app.Fragment#onDestroy()
*/
#Override
public void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
Log.e("onDestroy","onDestroy");
}
/* (non-Javadoc)
* #see android.support.v4.app.Fragment#onStart()
*/
#Override
public void onStart() {
// TODO Auto-generated method stub
super.onStart();
Log.e("onstart","onstart");
}
/* (non-Javadoc)
* #see android.support.v4.app.Fragment#onStop()
*/
#Override
public void onStop() {
// TODO Auto-generated method stub
super.onStop();
if(false){
Bundle savedInstance=getArguments();
LinearLayout viewParent;
viewParent= (LinearLayout) rootView.getParent();
viewParent.removeView(rootView);
}
parentView.removeView(rootView);
Log.e("onStop","onstop");
}
#Override
public void onPause() {
super.onPause();
Log.e("onpause","onpause");
}
#Override
public void onResume() {
super.onResume();
Log.e("onResume","onResume");
}
And here is the MainActivity:
/**
* Fragment managing the behaviors, interactions and presentation of the
* navigation drawer.
*/
private NavigationDrawerFragment mNavigationDrawerFragment;
/**
* Used to store the last screen title. For use in
* {#link #restoreActionBar()}.
*/
public static boolean fragment2InstanceExists=false;
public static Fragment2 fragment2=null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
setContentView(R.layout.activity_main);
mNavigationDrawerFragment = (NavigationDrawerFragment) getSupportFragmentManager()
.findFragmentById(R.id.navigation_drawer);
mTitle = getTitle();
// Set up the drawer.
mNavigationDrawerFragment.setUp(R.id.navigation_drawer,
(DrawerLayout) findViewById(R.id.drawer_layout));
}
#Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction=fragmentManager.beginTransaction();
switch(position){
case 0:
fragmentTransaction.addToBackStack(null);
fragmentTransaction.replace(R.id.container, Fragment1.newInstance(position+1)).commit();
break;
case 1:
Bundle bundle=new Bundle();
bundle.putInt("source_of_create",CommonMethods.CREATE_FROM_ACTIVITY);
if(!fragment2InstanceExists){
fragment2=Fragment2.newInstance(bundle);
fragment2InstanceExists=true;
}
fragmentTransaction.addToBackStack(null);
fragmentTransaction.replace(R.id.container, fragment2).commit();
break;
case 2:
fragmentTransaction.addToBackStack(null);
fragmentTransaction.replace(R.id.container, FolderExplorerFragment.newInstance(position+1)).commit();
break;
default:
break;
}
}
The parentView is the keypoint.
Normally, when onCreateView, we just use return rootView. But now, I add rootView to parentView, and then return parentView. To prevent "The specified child already has a parent. You must call removeView() on the ..." error, we need to call parentView.removeView(rootView), or the method I supplied is useless.
I also would like to share how I found it. Firstly, I set up a boolean to indicate if the instance exists. When the instance exists, the rootView will not be inflated again. But then, logcat gave the child already has a parent thing, so I decided to use another parent as a intermediate Parent View. That's how it works.
Hope it's helpful to you.

If you using bottombar and insted of viewpager you want to set custom fragment replacement logic with retrieve previously save state you can do using below code
String current_frag_tag = null;
String prev_frag_tag = null;
#Override
public void onTabSelected(TabLayout.Tab tab) {
switch (tab.getPosition()) {
case 0:
replaceFragment(new Fragment1(), "Fragment1");
break;
case 1:
replaceFragment(new Fragment2(), "Fragment2");
break;
case 2:
replaceFragment(new Fragment3(), "Fragment3");
break;
case 3:
replaceFragment(new Fragment4(), "Fragment4");
break;
default:
replaceFragment(new Fragment1(), "Fragment1");
break;
}
public void replaceFragment(Fragment fragment, String tag) {
if (current_frag_tag != null) {
prev_frag_tag = current_frag_tag;
}
current_frag_tag = tag;
FragmentManager manager = null;
try {
manager = requireActivity().getSupportFragmentManager();
FragmentTransaction ft = manager.beginTransaction();
if (manager.findFragmentByTag(current_frag_tag) == null) { // No fragment in backStack with same tag..
ft.add(R.id.viewpagerLayout, fragment, current_frag_tag);
if (prev_frag_tag != null) {
try {
ft.hide(Objects.requireNonNull(manager.findFragmentByTag(prev_frag_tag)));
} catch (NullPointerException e) {
e.printStackTrace();
}
}
// ft.show(manager.findFragmentByTag(current_frag_tag));
ft.addToBackStack(current_frag_tag);
ft.commit();
} else {
try {
ft.hide(Objects.requireNonNull(manager.findFragmentByTag(prev_frag_tag)))
.show(Objects.requireNonNull(manager.findFragmentByTag(current_frag_tag))).commit();
} catch (NullPointerException e) {
e.printStackTrace();
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
Inside Child Fragments you can access fragment is visible or not using below method
note: you have to implement below method in child fragment
#Override
public void onHiddenChanged(boolean hidden) {
super.onHiddenChanged(hidden);
try {
if(hidden){
adapter.getFragment(mainVideoBinding.viewPagerVideoMain.getCurrentItem()).onPause();
}else{
adapter.getFragment(mainVideoBinding.viewPagerVideoMain.getCurrentItem()).onResume();
}
}catch (Exception e){
}
}

Add different fragment to an activity based on Intent-given identifier

I'm working on an application where in layout layout-small-portrait I want to launch different fragments contained in a single "container activity", named SingleActivity. I will handle this differnetly in layouts layout-land, layout-large etc. but that is unrelated to my problem.
I have an activity MainActivity which is, as the name indicates, the main activity (launcher) of my application. This will initially contain a ListFragment with different items for the user to press.
Based on the item that the user presses the SingleActivity will launch and its content will correspond to a specific Fragment related to this item. My problem starts here. When the user presses an item I have a reference to the corresponding fragment I want to be displayed in SingleFragment. Illustrated below:
String tag = myFragmentReference.getTag();
Intent i = new Intent(this, SingleActivity.class);
i.putExtra(SingleActivity.CONST_TAG, tag);
startActivity(i);
The activity launches successfully. In SingleActivity I have the following onCreate() method:
...
// Retrieve the fragment tag from the intent
String tag = getIntent().getStringExtra(CONST_TAG);
Fragment fragment = getSupportFragmentManager().findFragmentByTag(tag);
if(fragment == null) {
// always end up here, this is my problem.
}
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.add(R.id.fragmentContainer, fragment);
ft.commit();
...
I suspect that the fact that fragment is always null is because the fragment has not been inflated yet. If I am right what I need to do is define a fragment's tag before it is inflated, so that it can be found by findFragmentByTag(). Is that possible?
If anything is unclear please let me know.
I look forward to hearing some good ideas! If there are better or more clever ways to implement this I would love to hear your thoughts! Thanks :)

Since you are jumping to another activity, it will have its own Fragment BackStack and that fragment will not exist.
You will have to inflate the fragment in the new activity something along these lines:
String tag = intent.getStringExtra(CONST_TAG);
if (getSupportFragmentManager().findFragmentByTag(tag) == null) {
Fragment fragment = Fragment.instantiate(this, tag, extras);
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.add(R.id.fragmentContainer, fragment, tag);
ft.commit();
}
The tag string will need to have the package location of the fragment such as "com.android.myprojectname.myfragment"

First use SlidingMenu library: https://github.com/jfeinstein10/SlidingMenu
This will help you, and your app will be more cool, that´s the only way that I can help you make what you need so, here is the code:
Here is your MainActivity:
I´ll try to explain this sample code and you use for your need.
This is the ListFragment of your BehindContent (SlidingMenu):
public class ColorMenuFragment extends ListFragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.list, null);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
String[] colors = getResources().getStringArray(R.array.color_names);
ArrayAdapter<String> colorAdapter = new ArrayAdapter<String>(getActivity(),
android.R.layout.simple_list_item_1, android.R.id.text1, colors);
setListAdapter(colorAdapter);
//This array is only to fill SlidingMenu with a Simple String Color.
//I used MergeAdapter from Commonsware to create a very nice SlidingMenu.
}
#Override
public void onListItemClick(ListView lv, View v, int position, long id) {
//This switch case is a listener to select wish item user have been selected, so it Call
//ColorFragment, you can change to Task1Fragment, Task2Fragment, Task3Fragment.
Fragment newContent = null;
switch (position) {
case 0:
newContent = new ColorFragment(R.color.red);
break;
case 1:
newContent = new ColorFragment(R.color.green);
break;
case 2:
newContent = new ColorFragment(R.color.blue);
break;
case 3:
newContent = new ColorFragment(android.R.color.white);
break;
case 4:
newContent = new ColorFragment(android.R.color.black);
break;
}
if (newContent != null)
switchFragment(newContent);
}
// the meat of switching the above fragment
private void switchFragment(Fragment fragment) {
if (getActivity() == null)
return;
if (getActivity() instanceof FragmentChangeActivity) {
FragmentChangeActivity fca = (FragmentChangeActivity) getActivity();
fca.switchContent(fragment);
} else if (getActivity() instanceof ResponsiveUIActivity) {
ResponsiveUIActivity ra = (ResponsiveUIActivity) getActivity();
ra.switchContent(fragment);
}
}
}
Here is your BaseActivity Class:
It dont have swipe, as I could understand, you don't need this.
public class FragmentChangeActivity extends BaseActivity {
private Fragment mContent;
public FragmentChangeActivity() {
super(R.string.changing_fragments);
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// set the Above View
if (savedInstanceState != null)
mContent = getSupportFragmentManager().getFragment(savedInstanceState, "mContent");
if (mContent == null)
mContent = new ColorFragment(R.color.red);
// set the Above View
//This will be the first AboveView
setContentView(R.layout.content_frame);
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.content_frame, mContent)
.commit();
// set the Behind View
//This is the SlidingMenu
setBehindContentView(R.layout.menu_frame);
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.menu_frame, new ColorMenuFragment())
.commit();
// customize the SlidingMenu
//This is opcional
getSlidingMenu().setTouchModeAbove(SlidingMenu.TOUCHMODE_FULLSCREEN);
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
getSupportFragmentManager().putFragment(outState, "mContent", mContent);
}
public void switchContent(Fragment fragment) {
// the meat of switching fragment
mContent = fragment;
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.content_frame, fragment)
.commit();
getSlidingMenu().showContent();
}
}
Ok, So If you want to change the ColorFragment to anything else, do this:
First, choice the item that you want to use:
case 0:
newContent = new ColorFragment(R.color.red);
break;
to:
case 0:
newContent = new ArrayListFragment();
break;
I have made just a arraylist, it is just a simple example, you can do a lot of thing, then you can read about Fragment to learn how to do different things.
public class ArrayListFragment extends ListFragment {
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setListAdapter(new ArrayAdapter<String>(getActivity(),
android.R.layout.simple_list_item_1, Listnames.TITLES));
//Listnames is a class with String[] TITLES;
}
#Override
public void onListItemClick(ListView l, View v, int position, long id) {
Log.i("FragmentList2", "Item clicked: " + id);
String item = (String) getListAdapter().getItem(position);
Toast.makeText(getActivity(), item, Toast.LENGTH_LONG).show();
}
}
As you see, it can display a different fragment based on which item in the ListFragment (MainActivity) the user presses.
Well, if you misunderstood something, just tell me.