Develop Reference

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.

Fragments stack Android

Imagine one activity with 3 fragments: starts showing the first one, select a menu option and go to the second one, select another option and go to the 3rd fragment and select again the first option an return to the second one.
f1 -> f2 -> f3 -> f2
When I press back I want the app returns to fragment 3 and when I press back again it should return to fragment 1 and if press back again, close the app.
Something like if the fragment exists, move it to top of the stack and if not, create it.
Thank you!

Here is solution I came up over time.
The idea is following, you need to keep a stack data structure and whenever you add a fragment add it to stack as well, then override onBackPress method and check if stack is not empty then replace your fragment container with new fragment from top of the stack when it is empty do super.onbackpress
So here is a parent class for all kind of fragment based navigation.
public abstract class FragmentsStackActivity extends BaseActivity {
public static final String TAG_BUNDLE = "bundle_tag";
protected final Bundle fragmentArgs = new Bundle();
protected Stack<Fragment> fragments = new Stack<>();
abstract protected void setupFragments();
public void setFragmentArguments(Fragment fragment, Bundle arguments){
if(!fragments.isEmpty() && fragments.peek()!=fragment){
fragment.setArguments(arguments);
}
}
public void setFragmentFromStack() {
if(!fragments.isEmpty()) {
Fragment fragment = fragments.peek();
final Fragment oldFragment = getSupportFragmentManager().findFragmentById(R.id.fragment_container);
if (oldFragment == null || oldFragment != fragment) {
getFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
final FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
//transaction.setCustomAnimations(R.anim.animator_left_right_in, R.anim.animator_left_right_in);
transaction.replace(R.id.fragment_container, fragment).commit();
}
}else {
finish();
}
}
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
//TODO need to save fragment stack
}
}
example of an activity that extends this class
public class LoginActivity extends FragmentsStackActivity{
private final MyFragment1 fragment1 = new MyFragment1();
private final MyFragment2 fragment2 = new MyFragment2();
private final User mUser = new User();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
setupFragments();
setFragmentFromStack();
}
#Override
protected void setupFragments() {
fragments.add(fragment2);
//fragment2.setNotifier(this); // I use notifiers listener but you can choose whatever convenient for you
Bundle fragmentArgs = new Bundle();
fragmentArgs.putBoolean(Constants.TAG_LOGIN, true);
fragmentArgs.putParcelable(User.TAG, mUser);
fragmentArgs.putInt(Constants.TYPE, getIntent().getIntExtra(Constants.TYPE, 0));
fragment2.setArguments(fragmentArgs);
//fragment1.setNotifier(this); // I use notifiers listener but you can choose whatever convenient for you
}
// this method teals with handling messages from fragments in order to provide navigation
// when some actions taken inside the fragment, you can implement your own version
public void onReceiveMessage(String tag, Bundle bundle) {
switch (tag) {
case MyFragment2.TAG_BACK:
case MyFragment1.TAG_BACK:
fragments.pop();
setFragmentFromStack();
break;
case MyFragment2.TAG_NEXT:
fragment1.setArguments(bundle);
fragments.add(fragment1);
setFragmentFromStack();
break;
case MyFragment1.TAG_NEXT:
goToWelcomeScreen(bundle);
finish();
break;
}
}
private void goToWelcomeScreen(Bundle bundle){
}
}

You can implement this with the help of the following code:
// transaction.replace(R.id.detailFragment, frag1);
Transaction.remove(null).add(frag1) // frag1 on view
// transaction.replace(R.id.detailFragment, frag2).addToBackStack(null);
Transaction.remove(frag1).add(frag2).addToBackStack(null) // frag2 on view
// transaction.replace(R.id.detailFragment, frag3);
Transaction.remove(frag2).add(frag3) // frag3 on view
And for better understanding, have a ook at the following snippet:
// Works with either the framework FragmentManager or the
// support package FragmentManager (getSupportFragmentManager).
getSupportFragmentManager().beginTransaction()
.add(detailFragment, "detail")
// Add this transaction to the back stack
.addToBackStack()
.commit();
getSupportFragmentManager().addOnBackStackChangedListener(
new FragmentManager.OnBackStackChangedListener() {
public void onBackStackChanged() {
// Update your UI here.
}
});
have a look here http://developer.android.com/training/implementing-navigation/temporal.html

update a listview in a fragment in a viewpager from activity

I understand that this is quite a common issue, and I have referred to many different other questions but I still can't get this to work.
My activity implements a view pager with two tabs and in each tab is a listview. I have a adapter for my view pager which links the two fragments and in each fragment, a adapter to link the data to the listview.
In my activity menu, I have a menu which creates an edittext in an alertdialog for me to input new fields into one of the listview in one of the fragment.
My activity (contains a viewpager)
protected void onCreate(Bundle savedInstanceState)
{
...
subAdapter = new SubAdapter(getSupportFragmentManager(), data);
((ViewPager) findViewById(R.id.viewPager)).setAdapter(subGroupAdapter);
}
My viewpager adapter
public class SubAdapter extends FragmentPagerAdapter
{
public SubGroupAdapter(FragmentManager fm, data data)
{
super(fm);
}
#Override
public Fragment getItem(int position)
{
Bundle bundle = new Bundle();
bundle.putString("data", data);
switch (position)
{
case 0:
Fragment1 frag1 = new Fragment1();
frag1.setArguments(bundle);
return frag1;
case 1:
Fragment2 frag2 = new Fragment2();
frag2.setArguments(bundle);
return frag2;
}
return null;
}//some other methods below
Fragment1 / Fragment2 (both fragments have a listview)
public void onActivityCreated(Bundle savedInstanceState)
{
super.onActivityCreated(savedInstanceState);
frag1Adapter = new frag1Adapter(this, data);
((ListView) getView().findViewById(R.id.listView)).setAdapter(frag1Adapter);
}
Custom listview adapter for both listviews in both fragments
public class ExpenseAdapter extends BaseAdapter implements OnClickListener
{ ... }
As I mentioned earlier, I can input a new entry into either listview from the activity action bar button. However, the listview does not get updated and I can't reference the listview adapter to call notifydatasetchanged() from the activity.
What is the best way I can proceed from here onwards? thank you so much!
I have tried exploring using interfaces, tags but can't get it to work currently.

What you should do is create a public method for your Fragment1 and Fragment2 like so:
define in your Activity:
Fragment1 frag1;
Fragment2 frag2;
then your ViewPager:
public class SubAdapter extends FragmentPagerAdapter
{
public SubGroupAdapter(FragmentManager fm, data data)
{
super(fm);
}
#Override
public Fragment getItem(int position)
{
Bundle bundle = new Bundle();
bundle.putString("data", data);
switch (position)
{
case 0:
frag1 = new Fragment1();
frag1.setArguments(bundle);
return frag1;
case 1:
frag2 = new Fragment2();
frag2.setArguments(bundle);
return frag2;
}
return null;
}
}
Put this method in Fragment1.java :
public void updateFragment1ListView(){
if(adapter != null){
adapter.notifyDataSetChanged();
}
}
and from your activity call:
if(frag1 != null){
frag1.updateFragment1ListView();
}
obviously change the names for your adapter if its not called adapter...
Just do the same for Fragment2.java as well

I would recommend creating an interface. Here's an Example:
public interface UpdateListFragmentInterface {
void updateList();
}
Then in the Activity, add the delegate as a property:
UpdateListFragmentInterface yourDelegate;
Wherever you create the Fragment within the Activity, assign the Fragment as the delegate:
// Set up and create your fragment.
(if yourFragment instanceof UpdateListFragmentInterface) {
yourDelegate = yourFragment;
}
Then in the Fragment, implement the interface:
public class YourListFragment extends android.support.v4.app.ListFragment implements UpdateListFragmentInterface {
// Constructors and other methods for the ListFragment up here.
// Override the interface method
public void updateList() {
//Update the list here.
}
}
Then finally, from within your Activity, when you need to update the list, simply call the delegate:
yourDelegate.updateList();
EDIT:
Sorry, I think you actually need to create a public method in your activity that is something like:
public void setUpdateListFragmentDelegate(UpdateListFragmentDelegate delegate) {
this.delegate = delegate
}
Then in the on attach of the List Fragment you will assign it there:
if (context instance of YourActivity) {
((YourActivity)context.setUpdateListFragmentDelegate(this);
}

"Can not perform this action after onSaveInstanceState" when fragment is replaced

In my project context, I have a Button b in a Fragment f(1) in an Activity a.
Fragment f(x) is an instance of F where content depends of argument x
I need to replace the current instance f(1) by an instance f(2) on b click event:
From Activity a:
private void setFragment(int x) {
Bundle args = new Bundle();
args.putInt("x", x);
F f = new F();
f.setArguments(args);
f.setListener(new F.Listener() {
public void onButtonClick(int x) {
setFragment(x);
}
});
getSupportFragmentManager()
.beginTransaction()
.replace(ID, f)
.commit();
}
From Fragment f:
b.setOnClickListener(new View.onClickListener() {
public void onClick(View view) {
listener.onButtonClick(x + 1);
}
});
My problem is:
An Exception is throw on b click event only if a configuration state change occurs:
java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
Please, what is my error? I read many posts on this Exception but I don't found any solution
Edit: I just make a test without AsyncTask, see the code:
Try to rotate the screen and push the button
public class MainActivity extends ActionBarActivity {
#Override
protected void onCreate(Bundle state) {
super.onCreate(state);
setContentView(R.layout.activity_main);
if (state == null) {
setFragment(1);
}
}
private void setFragment(int id) {
Bundle args = new Bundle();
args.putInt("id", id);
MyFragment myFragment = new MyFragment();
myFragment.setArguments(args);
myFragment.setListener(new MyFragment.Listener() {
#Override
public void onClick(int id) {
setFragment(id);
}
});
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.fragment, myFragment)
.commit();
}
public static class MyFragment extends Fragment{
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup view, Bundle state) {
return new Button(getActivity()) {
{
setText(String.valueOf(getArguments().getInt("id")));
setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
listener.onClick(getArguments().getInt("id") + 1);
}
});
}
};
}
private static interface Listener {
public void onClick(int id);
}
private Listener listener;
public void setListener(Listener listener) {
this.listener = listener;
}
}
}

The problem is the way you are setting the listener.
You are setting the listener, then you rotate your device from landscape to portrait. What happens after the rotation is:
Android create a brand new instance of MainActivity.
FragmentManager create a new instance of MyFragment internally and re-adds it automatically to the activity as it was before orientation change.
If you click on the button, the listener will be called. However, the listener is the listener of the previous activity (before rotation) which has been destroyed.
So not only you have a Memory Leak (the old activity can not be garbage collected, because it's referenced from here) but you also get this error.
How to do it correctly:
Well, the problem is NOT only setRetainInstanceState() you have not understood the Android Fragments lifecycle correctly. As mentioned above, Fragments are controlled by the FragmentManager (FragmentTransaction). So, yes everytime you rotate your screen a new Fragment instance will be created, but FragmentManager will attach them automatically for you (it's a little bit strange, but thats how Fragment works)
I would recommend to use an EventBus. The fragment will fire an Event onClick() and the activity will receive this event since it's subscribed. I recomment GreenDao EventBus.
Otherwise you can have a look at the official docs, but from my point of view they are teaching not a good solution, because your fragment and activity are hardly connected (not modular). They say you should use onAttach() like you can see in the sample from the documentation: http://developer.android.com/guide/components/fragments.html#EventCallbacks
Btw. a similar problem can occur if you are not using Fragment arguments for "passing" data. For more details read this blog: http://hannesdorfmann.com/android/fragmentargs/

Android: Replacing a fragment in a view pager

I have two fragments SearchFragment and CreateFragment in a view pager inside a activity called TicketManagementActivity. Now when the user presses the search button in SearchFragment, I want SearchFragment to be replaced with SearchResultFragment. I should then be able to swipe between SeachResultFragment and CreateFragment in the ViewPager. Also when I press back from SearchResultFragment I should go back to SearchFragment.
Right now, when I press the button I get a blank screen instead of the layout of SearchResultFragment. When I press back I get to SearchFragment but now I have to click the button twice for the blank screen to come. Now after the blank screen comes after the double click, whenever I swipe to CreateFragment tab I get a blank screen instead of CreateFragment layout.
I looked at quite a number of questions on SO but none of them seem to be working for me. Most useful seems to be the first two answers in this question, but the first answer doesn't handle the back press, nor am I able to implement it. The second answer seems very implementable but I get errors which I have mentioned below.
My main TicketManagemementActivity:
public class TicketManagementActivity extends FragmentActivity implements
ActionBar.TabListener {
ViewPager viewPager;
TabsPagerAdapter adapter;
ActionBar actionBar;
String[] tabs={"Search", "Create"};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_ticket_management);
viewPager=(ViewPager)findViewById(R.id.pager);
actionBar=getActionBar();
adapter=new TabsPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(adapter);
actionBar.setHomeButtonEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
for(String tab_name : tabs){
actionBar.addTab(actionBar.newTab().setText(tab_name).setTabListener(this));
}
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageSelected(int position) {
// on changing the page
// make respected tab selected
actionBar.setSelectedNavigationItem(position);
}
#Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
#Override
public void onPageScrollStateChanged(int arg0) {
}
});
}
//removed methods for menu creation and filling and placeholder fragment for brevity on SO
#Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
viewPager.setCurrentItem(tab.getPosition());
}
#Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
#Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
}
My activity_ticket_management.xml which is layout set in onCreate of ticket management activity, just contains the viewpager
<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.v4.view.ViewPager>
My TabsPagerAdapter class extending FragmentPagerAdapter:
public class TabsPagerAdapter extends FragmentPagerAdapter {
public TabsPagerAdapter(android.support.v4.app.FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int index) {
switch (index) {
case 0:
// Top Rated fragment activity
return new SearchFragment();
case 1:
// Games fragment activity
return new CreateFragment();
}
return null;
}
#Override
public int getCount() {
// get item count - equal to number of tabs
return 2;
}
}
Relevant part of my SearchFragment:
public class SearchFragment extends Fragment implements View.OnClickListener {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_search, container, false);
.
.//some widget initializations
.
return rootView;
}
#Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.ticket_search_btn: searchSigmaTickets();
break;
}
}
public void searchSigmaTickets(){
.
.
.
.//some operations
.
new SearchAsyncTask().execute();
}
}
private class SearchAsyncTask extends AsyncTask<Void, Void, Void>{
protected Void doInBackground(Void... params){
.
.//some more operation
.
}
protected void onPostExecute(Void param){
Fragment newFragment = new SearchResultFragment();
//Here I use getFragmentManager and not getChildFragmentManager
FragmentTransaction transaction = getFragmentManager().beginTransaction();
//HERE I try to replace the fragment. I'm not sure what id to pass, I pass the id of the main veiwpager in ticketmanagement activity
transaction.replace(R.id.pager, newFragment);
transaction.addToBackStack(null);
transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
transaction.commit();
}
}
}
If I use getChildFragmentManager instead of getFragmentManager as mentioned in the second answer I get
06-25 06:55:32.045: E/AndroidRuntime(2797): java.lang.IllegalArgumentException: No view found for id 0x7f06003c (com.amberroad.sigmaticket:id/pager) for fragment SearchResultFragment{b2fed358 #0 id=0x7f06003c}
Sorry for the lengthy question, how should I solve this?

Kartik, get ready for a lengthy answer to your lenghty question. Replacing fragments in a viewpager is quite involved but is very possible and can look super slick. First, you need to let the viewpager itself handle the removing and adding of the fragments. What is happening is when you replace the fragment inside of SearchFragment, your viewpager retains its fragment views. So you end up with a blank page because the SearchFragment gets removed when you try to replace it.
The solution is to create a listener inside of your viewpager that will handle changes made outside of it so first add this code to the bottom of your adapter.
public interface nextFragmentListener {
public void fragment0Changed(String newFragmentIdentification);
}
Then you need to create a private class in your viewpager that becomes a listener for when you want to change your fragment. For example you could add something like this. Notice that it implements the interface that was just created. So whenever you call this method, it will run the code inside of the class below.
private final class fragmentChangeListener implements nextFragmentListener {
#Override
public void fragment0Changed(String fragment) {
//I will explain the purpose of fragment0 in a moment
fragment0 = fragment;
manager.beginTransaction().remove(fragAt0).commit();
switch (fragment){
case "searchFragment":
fragAt0 = SearchFragment.newInstance(listener);
break;
case "searchResultFragment":
fragAt0 = Fragment_Table.newInstance(listener);
break;
}
notifyDataSetChanged();
}
There are two main things to point out here: 1)fragAt0 is a "flexible" fragment. It can take on whatever fragment type you give it. This allows it to become your best friend in changing the fragment at position 0 to the fragment you desire. 2) Notice the listeners that are placed in the 'newInstance(listener)constructor. These are how you will callfragment0Changed(String newFragmentIdentification)`. The following code shows how you create the listener inside of your fragment.
static nextFragmentListener listenerSearch;
public static Fragment_Journals newInstance(nextFragmentListener listener){
listenerSearch = listener;
return new Fragment_Journals();
}
You could then call the change inside of your onPostExecute
private class SearchAsyncTask extends AsyncTask<Void, Void, Void>{
protected Void doInBackground(Void... params){
.
.//some more operation
.
}
protected void onPostExecute(Void param){
listenerSearch.fragment0Changed("searchResultFragment");
}
}
This would trigger the code inside of your viewpager to switch your fragment at position zero fragAt0 to become a new searchResultFragment. There are two more small pieces you would need to add to the viewpager before it became functional.
One would be in the getItem override method of the viewpager.
#Override
public Fragment getItem(int index) {
switch (index) {
case 0:
//this is where it will "remember" which fragment you have just selected. the key is to set a static String fragment at the top of your page that will hold the position that you had just selected.
if(fragAt0 == null){
switch(fragment0){
case "searchFragment":
fragAt0 = FragmentSearch.newInstance(listener);
break;
case "searchResultsFragment":
fragAt0 = FragmentSearchResults.newInstance(listener);
break;
}
}
return fragAt0;
case 1:
// Games fragment activity
return new CreateFragment();
}
Now without this final piece you would still get a blank page. Kind of lame, but it is an essential part of the viewPager. You must override the getItemPosition method of the viewpager. Ordinarily this method will return POSITION_UNCHANGED which tells the viewpager to keep everything the same and so getItem will never get called to place the new fragment on the page. Here's an example of something you could do
public int getItemPosition(Object object)
{
//object is the current fragment displayed at position 0.
if(object instanceof SearchFragment && fragAt0 instanceof SearchResultFragment){
return POSITION_NONE;
//this condition is for when you press back
}else if{(object instanceof SearchResultFragment && fragAt0 instanceof SearchFragment){
return POSITION_NONE;
}
return POSITION_UNCHANGED
}
Like I said, the code gets very involved, but you basically have to create a custom adapter for your situation. The things I mentioned will make it possible to change the fragment. It will likely take a long time to soak everything in so I would be patient, but it will all make sense. It is totally worth taking the time because it can make a really slick looking application.
Here's the nugget for handling the back button. You put this inside your MainActivity
public void onBackPressed() {
if(mViewPager.getCurrentItem() == 0) {
if(pagerAdapter.getItem(0) instanceof FragmentSearchResults){
((FragmentSearchResults) pagerAdapter.getItem(0)).backPressed();
}else if (pagerAdapter.getItem(0) instanceof FragmentSearch) {
finish();
}
}
}
You will need to create a method called backPressed() inside of FragmentSearchResults that calls fragment0changed. This in tandem with the code I showed before will handle pressing the back button. Good luck with your code to change the viewpager. It takes a lot of work, and as far as I have found, there aren't any quick adaptations. Like I said, you are basically creating a custom viewpager adapter, and letting it handle all of the necessary changes using listeners
Here is the code all together for the TabsPagerAdapter.
public class TabsPagerAdapter extends FragmentPagerAdapter{
Fragment fragAt0;
fragmentChangeListener listener = new fragmentChangeListener();
FragmentManager manager;
static String fragment0 = "SearchFragment";
//when you declare the viewpager in your adapter, pass it the fragment manager.
public viewPager(FragmentManager fm) {
super(fm);
manager = fm;
}
private final class fragmentChangeListener implements nextFragmentListener {
#Override
public void fragment0Changed(String fragment) {
//I will explain the purpose of fragment0 in a moment
fragment0 = fragment;
manager.beginTransaction().remove(fragAt0).commit();
switch (fragment){
case "searchFragment":
fragAt0 = SearchFragment.newInstance(listener);
break;
case "searchResultFragment":
fragAt0 = Fragment_Table.newInstance(listener);
break;
}
notifyDataSetChanged();
}
}
#Override
public Fragment getItem(int index) {
switch (index) {
case 0:
//this is where it will "remember" which fragment you have just selected. the key is to set a static String fragment at the top of your page that will hold the position that you had just selected.
if(fragAt0 == null){
switch(fragment0){
case "searchFragment":
fragAt0 = FragmentSearch.newInstance(listener);
break;
case "searchResultsFragment":
fragAt0 = FragmentSearchResults.newInstance(listener);
break;
}
}
return fragAt0;
case 1:
// Games fragment activity
return new CreateFragment();
}
#Override
public int getCount() {
// Show 3 total pages.
return 3;
}
#Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
String[] tab = {"Journals", "Charts", "Website"};
switch (position) {
case 0:
return tab[0].toUpperCase(l);
case 1:
return tab[1].toUpperCase(l);
case 2:
return tab[2].toUpperCase(l);
}
return null;
}
public int getItemPosition(Object object)
{
//object is the current fragment displayed at position 0.
if(object instanceof SearchFragment && fragAt0 instanceof SearchResultFragment){
return POSITION_NONE;
//this condition is for when you press back
}else if{(object instanceof SearchResultFragment && fragAt0 instanceof SearchFragment){
return POSITION_NONE;
}
return POSITION_UNCHANGED
}
public interface nextFragmentListener {
public void fragment0Changed(String fragment);
}