Here, I have a Activity with a ViewPager, it has 4 tabs, here is the activity screen shot link.
Here is the screen shot for tab 4, when the screen is vertical.
when the activity is opened, I switch to the fourth tab, and then switch to the second, rotate the screen, part of the fourth tab will overlay on the second tab, but when switch to the first and the third, it won't happen,
the picture is as following:
tab 4:
tab 1:
tab 2:
How could I have solved this problem?
following is the adapter of viewpager:
public class MainPageFragmentPageAdapter extends FragmentPagerAdapter {
SparseArray<Fragment> fragmentSparseArray = new SparseArray<Fragment>();
private Fragment currentSelectedFragment;
public MainPageFragmentPageAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
if (fragmentSparseArray.get(position) == null) {
Fragment fragment = null;
switch (position) {
case 0:
fragment = new NewHomePageFragment();
break;
case 1:
fragment = new NewDiscoverFragment();
break;
case 2:
fragment = new NewUserMessageFragment();
break;
case 3:
fragment = new NewUserDetailFragment();
}
fragmentSparseArray.put(position, fragment);
}
currentSelectedFragment = fragmentSparseArray.get(position);
return currentSelectedFragment;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
}
#Override
public int getCount() {
return 4;
}
public Fragment getCurrentSelectedFragment() {
return currentSelectedFragment;
}
}
Any code you want to see please comment below.
As you said, You do not destroyItem when pager is not visible,so it will still in memory,and redraw it
Please manage screen orientation through onConfigurationChanged Android method.
Related
When I open the application for the first time my tab is working fine. When I come back and go to the fragment page some times it returns null. Please help me ! What am I doing wrong? Here is my code.
public class TabsFragmentPagerAdapter extends FragmentPagerAdapter {
private ArrayList<ShareWinLeaderBoardTabModel> mShareWinLeaderBoardTabModelList;
public TabsFragmentPagerAdapter(FragmentManager fragmentManager, ArrayList<ShareWinLeaderBoardTabModel> shareWinLeaderBoardTabModelList) {
super(fragmentManager);
mShareWinLeaderBoardTabModelList = shareWinLeaderBoardTabModelList;
}
#Override
public Fragment getItem(int position) {
/*ShareWinLeaderBoardTabModel model = Once that is donemShareWinLeaderBoardTabModelList.get(position);
return new ShareWinLeaderBoardListFragment(model);*/
switch (position) {
case 0:
ShareWinLeaderBoardTabModel model = mShareWinLeaderBoardTabModelList.get(position);
return new ShareWinLeaderBoardListFragment(model);
case 1:
ShareWinLeaderBoardTabModel model1 = mShareWinLeaderBoardTabModelList.get(position);
return new ShareWinLeaderBoardListFragment(model1);
case 2:
ShareWinLeaderBoardTabModel model2 = mShareWinLeaderBoardTabModelList.get(position);
return new ShareWinLeaderBoardListFragment(model2);
case 3:
ShareWinLeaderBoardTabModel model3 = mShareWinLeaderBoardTabModelList.get(position);
return new ShareWinLeaderBoardListFragment(model3);
default:
return null;
}
}
#Override
public int getCount() {
return mShareWinLeaderBoardTabModelList.size();
}
}
When I press back there is some problem with the tab host. Tabs are coming fine but they are showing blank fragments. Any Help?
Image:
Change FragmentPagerAdapter to FragmentStatePagerAdapter
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);
}
The application has a main activity (MainActivity.java) with three tabs (fragments). I can navigate between them using the swipe left (riht) or clicking on a specific tab.
Upon starting the application, the 1st fragment is shown.
If I go to the 2nd fragment from the 1st fragment and then back to the 1st fragment, nothing happens (onResume() of the 1rd fragment isn't called), so it doesn't refresh it's content.
If I go to the 3rd fragment from the 1st fragment and then directly back to the 1st fragment, the onCreateView() of fragment1 is created and it's onResume() is called, which is correct.
If I go from the 3rd fragment to the 2nd fragment, the onCreateView() and onResume() of fragment1 are called, but not the onCreateView of fragment2.
I guess the logic in MainActivity isn't right, so I would kindly ask someone to take a look and tell me what could be wrong.
MainActivity.java:
public class MainActivity extends FragmentActivity implements ActionBar.TabListener {
CollectionPagerAdapter mCollectionPagerAdapter;
public TTSocket socket;
DBHandler db;
public String logged_user;
private LogedinPerson person;
ViewPager mViewPager;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Bundle extras = getIntent().getExtras();
logged_user = extras.getString("logged_user");
socket = TTSocket.getInstance();
socket.currentRef = this;
db = new DBHandler(this);
person=db.getLogedInPerson();
socket.dbHandler=db;
socket.person=person;
if(!socket.isInit){
String typeInitStr = "{\"Type\":\"Init\", \"UserId\":\""+ person.getUserId() +"\"}";
socket.Send(typeInitStr);
}
mCollectionPagerAdapter = new CollectionPagerAdapter(getSupportFragmentManager());
// Set up action bar.
final ActionBar actionBar = getActionBar();
// Specify that we will be displaying tabs in the action bar.
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Set up the ViewPager, attaching the adapter and setting up a listener
// for when the
// user swipes between sections.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mCollectionPagerAdapter);
mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int position) {
Log.d("TEST",position+"");
// the corresponding tab.
// We can also use ActionBar.Tab#select() to do this if
// we have a reference to the Tab
actionBar.setSelectedNavigationItem(position);
}
});
// For each of the sections in the app, add a tab to the action bar.
for (int i = 0; i < mCollectionPagerAdapter.getCount(); i++) {
// Create a tab with text corresponding to the page title defined by
// the adapter.
// Also specify this Activity object, which implements the
// TabListener interface, as the
// listener for when this tab is selected.
if(i == 0){
actionBar.addTab(actionBar.newTab()
.setIcon(R.drawable.messages)
.setTabListener(this));
}else if(i == 1){
actionBar.addTab(actionBar.newTab()
.setIcon(R.drawable.contacts)
.setTabListener(this));
}else{
actionBar.addTab(actionBar.newTab()
.setIcon(R.drawable.history)
.setTabListener(this));
}
}
}
#Override
protected void onResume() {
// TODO Auto-generated method stub
super.onResume();
socket.currentRef = this;
socket.dbHandler=db;
socket.person=person;
//mCollectionPagerAdapter.notifyDataSetChanged();
}
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
// When the given tab is selected, switch to the corresponding page in
// the ViewPager.
mViewPager.setCurrentItem(tab.getPosition());
}
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
/**
* A {#link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the primary sections of the app.
*/
public class CollectionPagerAdapter extends FragmentPagerAdapter {
final int NUM_ITEMS = 3; // number of tabs
public CollectionPagerAdapter(FragmentManager fm) {
super(fm);
}
/*
#Override
public Fragment getItem(int i) {
Fragment fragment = new TabFragment();
Bundle args = new Bundle();
args.putInt(TabFragment.ARG_OBJECT, i);
fragment.setArguments(args);
return fragment;
}
*/
#Override
public Fragment getItem(int position) {
Fragment fragment = new Fragment();
Bundle args = new Bundle();
args.putInt(TabFragment.ARG_OBJECT, position);
switch (position) {
case 0:
Log.i("Fragment", "0");
fragment = new Tab1Fragment();
fragment.setArguments(args);
return fragment;
case 1:
Log.i("Fragment", "1");
fragment = new Tab2Fragment();
fragment.setArguments(args);
return fragment;
case 2:
Log.i("Fragment", "2");
fragment = new Tab3Fragment();
fragment.setArguments(args);
return fragment;
default:
break;
}
return fragment;
}
#Override
public int getCount() {
return NUM_ITEMS;
}
#Override
public CharSequence getPageTitle(int position) {
String tabLabel = null;
switch (position) {
case 0:
tabLabel = getString(R.string.label1);
break;
case 1:
tabLabel = getString(R.string.label2);
break;
case 2:
tabLabel = getString(R.string.label3);
break;
}
return tabLabel;
}
}
/**
* A fragment that launches other parts of the demo application.
*/
public static class TabFragment extends Fragment {
public static final String ARG_OBJECT = "object";
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
Bundle args = getArguments();
int position = args.getInt(ARG_OBJECT);
int tabLayout = 0;
switch (position) {
case 0:
tabLayout = R.layout.tab1;
break;
case 1:
tabLayout = R.layout.tab2;
break;
case 2:
tabLayout = R.layout.tab3;
break;
}
View rootView = inflater.inflate(tabLayout, container, false);
return rootView;
}
}
}
Strange onPause(), onResume() behaviour() in fragments
It's not strange behaviour but native behaviour of ActionSherlock. This kind of behaviour is used for caching -> optimalisation for older devices with lower RAM this is reason why fragments are cached.
If you need to update content of fragment don't try to replace its layout or something similar. If you want to update fragment when scrolling between pages, you need to use method of FragmentPagerAdapter:
#Override
public int getItemPosition(Object object) {
// implementation
return super.getItemPosition(object);
}
This method is called when you will call
notifyDataSetChanged();
on your FragmentPagerAdapter. It's handy method for make updates of your fragments. There are more ways how to do it but here i'll show you how I'm doing it.
Let your fragments implement interface for example called Updateable:
interface Updateable {
public void update();
}
public class MyFragment extends SherlockFragment implements Updateable {
#Override
public void update() {
// perform Fragment updates
}
}
And in this method you will perform updates. Now back to getItemPosition() method. This method will be used for invoking update() method from Fragment i.e:
#Override
public int getItemPosition(Object object) {
Fragment f = (Fragment) object;
// determine which fragment
if (f instanceof MyFragment) {
((MyFragment) f).update(); // invokes update() method
}
return super.getItemPosition(object);
}
Now whenever you scroll page or tap on some tab (you need also call notifyDataSetChanged()) you are able to make Fragment updates. This way is more efficient against destroying and recreating fragment(s) each time you scrolling or clicking on tabs. But how i said this is not only solution there are more possible solutions.
Note: getItemPosition() can return two values: POSITION_NONE and UNCHANGED. Difference between both is that first indicates that Fragment will be always destroyed and recreated that is not very efficient and second indicates that Fragment won't be changed (is in on right place).
For more detailed explanation look here.
That is because ViewPager doesn't hide all fragments you switch.
You can control this behaviour by setOffscreenPageLimit
I am finally catching up with the Android 4.0+ world and switching my activities to fragments. I am implementing the swipe view style tabs and need to be able to disable tabs based on an extra I am passing into the activity. My old way of doing this was this, but I can't seem to figure out how to do this with swipe views.
tabHost.getTabWidget().getChildAt(1).setVisibility(View.GONE);
The tabHost no longer applies. Now I have a FragmentPagerAdapter and ViewPager, but no clue how to use them to disable the tab. Thanks in advance for any pointers!
I managed to determine how to do this, however I don't know that it is the best way. What I had to do was pass a boolean value into my implementation of the FragmentPagerAdapter and only allow create the one fragment if I am in search mode.
/**
* A {#link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
boolean isSearching = false;
public SectionsPagerAdapter(FragmentManager fm, boolean isSearching) {
super(fm);
this.isSearching = isSearching;
}
#Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
Fragment fragment = null;
switch (position) {
case 0:
fragment = new UserGeneralFragment();
break;
case 1:
if (!isSearching) fragment = new CommentListFragment();
break;
}
return fragment;
}
#Override
public int getCount() {
if (!isSearching) return 2;
else return 1;
}
#Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 0:
return getString(R.string.activity_user_tab_general).toUpperCase(l);
case 1:
if (!isSearching) return getString(R.string.activity_user_tab_comments).toUpperCase(l);
break;
}
return null;
}
}
I have 3 pages in a ViewPager: instances of Tab0, Tab1, Tab2. In the main Activity, I'm storing the instance of each tab in separte variables from the SectionsPagerAdapter's getItem() function.
I assume that ViewPager always initializes the current tab, the tab to the left of it, and the tab to the right of it.
These are my instances: Tab0 t0; Tab1 t1; Tab2 t2;
The app works fine initially. But if i press the home button (to trigger onPause()), kill the app from task killer (or assume that android itself has killed it), and open the app again, i get NullPointerExceptions in onPageSelected because t0, t1 and t2 are now null.
This is my onCreate method:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mSectionsPagerAdapter = new SectionsPagerAdapter(
getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mSectionsPagerAdapter);
mViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageSelected(int pos) {
switch(pos){
case 1:
t1.lookup()
break;
case 0:
t0.doSomething();
break;
case 2:
t2.someThingElse();
break;
}
}
#Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
#Override
public void onPageScrollStateChanged(int arg0) {
}
});
mViewPager.setCurrentItem(1,true);
}
This is my FragmentPagerAdapter (which is a nested class inside my Activity):
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a DummySectionFragment (defined as a static inner class
// below) with the page number as its lone argument.
Fragment fragment;
switch(position){
case 0:
fragment = t0 = new Tab0();
break;
case 1:
fragment = t1 = new Tab1();
break;
case 2:
fragment = t2 = new Tab2();
break;
default:
fragment=null;
}
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, position + 1);
if(fragment!=null)
fragment.setArguments(args);
return fragment;
}
#Override
public int getCount() {
// Show 3 total pages.
return 3;
}
#Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 1:
return getString(R.string.T1).toUpperCase(l);
case 0:
return getString(R.string.T0).toUpperCase(l);
case 2:
return getString(R.string.T2).toUpperCase(l);
}
return null;
}
}
From the Docs:
The fragment of each page the user visits will be kept in memory, though its view hierarchy may be destroyed when not visible. Meaning when it comes back the fragments will be recreated for you but will not be the original ones(hence your loss of t* variables). I'd take a look at overriding saveState and restoreState methods to see if you can add the logic for setting up what the t* variables. If not perhaps in one of the other on* methods in the fragment.