The background
I have single activity in my App which loads 2 fragments based on some menu item selection
public class ActivityMain extends AppCompatActivity{
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState == null) {
loadFragment(1); // DEFAULT FRAGMENT, AT THE BEGINNING
}
}
..........................
..........................
// This method is called above, ALSO onItemClick in the Navigation Drawer (code not included for brevity)
public void loadFragment(int position) {
Fragment fragment = null;
switch (position) {
case 1:
fragment = new Fragment1();
break;
case 2:
fragment = new Fragment2();
break;
default:
break;
}
if (fragment != null) {
getFragmentManager().beginTransaction().replace(R.id.fragment_container, fragment, "frag_" + position).addToBackStack(null).commit();
}
}
}
"Fragment1" is a simple fragment with a fixed text in a TextView. "Fragment2" uses SlidingTabLayout to load a Fragment "FragmentViewPager" in a viewpager using FragmentStatePagerAdapter.
The issue I am facing:
Even if I remove "Fragment2" from the Activity's Frame Layout (using getFragmentManager().beginTransaction().remove), Fragment "FragmentViewPager" does not get destroyed, rather it resumes every time Activity resumes.
Question
Why FragmentViewPager is not destroyed with "Fragment2"?
If you are using FragmentStatePagerAdapter then this will not destroy fragment and when you swipe and come back to that fragment it will show old data without refresh. Because of not destroyed by viewpager.
I am currently working on an application with ActionBar tabs inside one of its fragments (main navigation is NavigationDrawer). The fragment's onCreate():
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
actionBar = activity.getActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
Resources r = getResources();
//(…) tabNames initialization
adapter = new CustomTabAdapter(getFragmentManager());
}
and onCreateView():
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment, container, false);
viewPager = (ViewPager) rootView.findViewById(R.id.pager);
viewPager.setAdapter(adapter);
viewPager.addOnPageChangeListener(this);
for (String tabName : tabNames) {
actionBar.addTab(actionBar.newTab()
.setText(tabName)
.setTabListener(this));
}
return rootView;
}
There are 4 tabs, each of them with its own Fragment and layout. CustomTabAdapter returns new instance of proper fragment in its getItem(int). There are 4 tabs.
And now my problem is:
I start the application.
I choose this tab fragment from NavigationDrawer list. Everything is working just fine.
I choose another fragment from NavigationDrawer list which means that tab fragment is replaced with it.
I choose tab fragment again. And fragment related to tab that was selected before choosing another fragment from NavigationDrawer list, and one's adjacent to it are not recreated (blank screen under ActionBar tabs). I checked and onCreateView(…) methods of those fragment are not called. So after changing device orientation, or choosing tab not adjacent and this one again proper layout is shown.
How can I make it work as it should (showing proper layout on reentering tab fragment from NavigationDrawer list instead of blank space)? I run out of ideas.
Finally, I found a solution. My CustomTabAdapter was extension of FragmentPagerAdapter. I changed it to be extension of FragmentStatePageAdapter, and now fragments are recreated.
More details in this answer by #Louth.
It takes fragments from cache without recreation
I want to show a same fragment for example fragment having activities of a day of week in a viewpager for all days with different data. I will be giving the dayNumber parameter to each fragment being instantiated and showing related activities. The problem is I see same fragment in each tab no matter what parameter I passed. I think the last fragment added or instantiated by a pager overrides all the other tab fragments instance. Because when I open a list item in expendableList View it is opened in all fragments of the pager.
This is how I am using the pager and fragment.
Pager
mPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int position) {
// When swiping between pages, select the
// corresponding tab.
if (bar.getNavigationMode() == ActionBar.NAVIGATION_MODE_TABS)
if (bar.getSelectedNavigationIndex() != position)
bar.setSelectedNavigationItem(position);
// should be changed when some solution comes.
if (tab == 0) {
Fragment ev;
if ((ev = (Fragment) mPagerAdapter.instantiateItem(mPager,
0)) instanceof frTimetable)
((frTimetable) ev).refresh(day.Monday);
} else if (tab == 1) {
Fragment ac;
if ((ac = (Fragment) mPagerAdapter.instantiateItem(mPager,
1)) instanceof frTimetable)
((frTimetable) ac).refresh(day.Tuesday);
}
tab = position;
}
Fragement
{
//class other methods
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fr_timetable, container, false);
ExpandList = (ExpandableListView) view.findViewById(R.id.expActivityView);
//I will change the list items in refresh method of the fragment for a day type
ExpListItems = new ArrayList<Items>(Timetable_Provider.getAllActivites());
ExpAdapter = new ExpandListAdapter(getActivity(), ExpListItems);
ExpandList.setAdapter(ExpAdapter);
return view;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
}
instantiateItem() is certainly not what you want. That is called by ViewPager, not by a consumer of a ViewPager.
Normally, you would provide the data to the ViewPager as part of setting up the pages, inside of your PagerAdapter. For example, this sample app uses the arguments Bundle to pass the page number of the page to the Fragment that is the implementation of the page.
If the data inside a page needs to be updated, ideally the page itself determines on its own that this is needed and handles it. Or, use an event bus (e.g., LocalBroadcastManager, greenrobot's EventBus, Square's Otto) to publish information that relevant pages can pick up. There is no great way to get at an existing page from outside of the page itself using FragmentPagerAdapter or FragmentStatePagerAdapter (e.g., to have an activity push data into a page), which is one of the reasons I wrote ArrayPagerAdapter.
I need your help regarding my application flow.
MainActivity (with Navigation Drawer)
-- Fragment A
-- Fragment B
-- Fragment C (articles list view)
ArticleActivity
-- Fragment D (article detail view)
Fragment C (MainActivity) displays a list of items (ListView). Selecting an item leads to fragment D (handle by ArticleActivity) which presents that item in more detail.
Fragment D displays a "Up" button that should allow the user to returns to previous screen (the detail view). The problem is that when the "Up" button is pressed the previous activity is displayed but not the previous activated fragment (the defaut fragment (A) is instead displayed).
My current code:
public class FragmentC extends Fragment {
public static FragmentC newInstance() {
FragmentC fragment = new FragmentC();
return fragment;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_courses, container, false);
...
// Somewhere in my code I have a onClickListener to launch the detail view activity
setOnClickListener(new OnCardClickListener() {
#Override
public void onClick(Card card, View view) {
Intent i = new Intent(getActivity(), ArticleActivity.class);
i.putExtra("articleIndex", mArticle.getId());
startActivity(i);
}
});
...
return view;
}
}
public class ArticleActivity extends Activity {
private long mArticleIndex;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_course);
mArticleIndex = getIntent().getExtras().getLong("articleIndex", 0);
// Set up action bar:
// Specify that the Home button should show an "Up" caret, indicating that touching the
// button will take the user one step up in the application's hierarchy.
final ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
// Place an ArticleFragment as our content pane
ArticleFragment fragment = ArticleFragment.newInstance(mArticleIndex);
getFragmentManager().beginTransaction().replace(R.id.container, fragment).commit();
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This is called when the Home (Up) button is pressed in the action bar.
Intent upIntent = new Intent(this, MainActivity.class);
upIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(upIntent);
finish();
return true;
}
return super.onOptionsItemSelected(item);
}
}
I think that I can resolve this issue by passing parameters to my Intent. For example i.putExtra("displayFragment", FragmentD) and then on the MainActivity retrieve it and tell to the FragmentManager to display the wanted fragment. I do not know if it's can work.
But it's maybe not the right way to achieve that?
Do you have any better workaround?
I have ActionBar Tabs setup. It consists of 4 tabs. Everything is fine until I navigate away from TabbedFragment and returning back.
I create tabs like this:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final ActionBar actionBar = getActionBar();
tabs = Lists.newArrayList();
tabs.add(new TabDefinition<>("Tab 1"));
tabs.add(new TabDefinition<>("Tab 2"));
tabs.add(new TabDefinition<>("Tab 3"));
tabs.add(new TabDefinition<>("Tab 4"));
for (TabDefinition tab : tabs) {
actionBar.addTab(actionBar.newTab()
.setText(tab.text)
.setTag(tab.tag)
.setTabListener(this));
}
}
And initialize adapter like this:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.paging_tab_container, container, false);
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
viewPager = (ViewPager) view.findViewById(R.id.pager);
viewPager.setAdapter(new FragmentStatePagerAdapter(getFragmentManager()) {
#Override
public Fragment getItem(int position) {
return tabs.get(position).fragment;
}
#Override
public int getCount() {
return tabs.size();
}
});
viewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int position) {
getActionBar().setSelectedNavigationItem(position);
}
});
viewPager.setCurrentItem(getActionBar().getSelectedNavigationIndex(), true);
}
When returning back to TabbedFragment selected tab and 1 next to it would not have any content. Just empty view. But if I select current + 2 fragment content is loaded. And then returning to that first fragment content is reloaded.
For example I have A, B, C, D tabs. Before leaving TabbedFragment I had selected tab A.
When returning to TabbedFragment I still am at tab A, but it's empty. So is tab B.
But when selecting tab C it is created and loaded. Returning to tab A it is recreated.
What could be the problem here?
After a while ran into the same problem again, so updating this question.
If you're using FragmentStatePagerAdapter you should provide FragmentManager via getChildFragmentManager() instead of getFragmentManager(). See Issue 55068: ViewPager doesn't refresh child fragments when back navigation via backstack
Okay so When using a FragmentStatePagerAdapter your fragments will be destroyed when you navigate anymore than one fragment Away since by default offScreenPageLimit is set to 1 by default just as mentioned above.
Typically this Class is used for an activity that has a very large set of Fragments, i.e have to scroll through a large amount of views. If your application does not need more than say 3-4 tabs I would suggest using FragmentPagerAdapter instead, and then specifying your offScreenPageLimit to something like 3, so if you get to the 4th Tab, all 3 tabs before will still be in memory.
Here is some Sample Code for a project on github that i created illustrating how to dynamically load the fragments if you don't want to add this offScreenPageLimit.
https://github.com/lt-tibs1984/InterfaceDemo/blob/master/src/com/divshark/interfacedemo/InterfaceDemoMain.java
Walk through all this code in this Class, and you will see how I'm dynamically loading the fragments, each time my ViewPager is slid over. Most notably at the bottom.
You can download this code, and use it as a test base for what you want to do.
Try adding the setOffScreenPageLimit(2) in the onCreate() method for the viewPager and notice the different behavior. To check the behavior, edit the text in fragment 1. Navigate Away and navigate back, with this set or not. You will see when it is set, the fragment's text remains what you change it to, since the fragment is never recreated.
Please provide additional questions if you have them.
GoodLuck
UPDATE
private static final String [] fragmentClasses = {"com.example.project.YourFragment1","com.example.project.YourFragment2","com.example.project.YourFragment3"};
viewPager.setAdapter(new FragmentStatePagerAdapter(getFragmentManager()) {
#Override
public Fragment getItem(int position) {
Fragment fragmentAtPosition = null;
// $$$$ This is the Important Part $$$$$
// Check to make sure that your array is not null, size is greater than 0 , current position is greater than equal to 0, and position is less than length
if((fragmentClasses != null) && (fragmentClasses.length > 0)&&(position >= 0)&& (position < fragmentClasses.length))
{
// Instantiate the Fragment at the current position of the Adapter
fragmentAtPosition = Fragment.instantiate(getBaseContext(), fragmentClasses[position]);
fragmentAtPosition.setRetainInstance(true);
}
return fragmentAtPosition;
}
#Override
public int getCount() {
return fragmentClasses.length;
}
});
The problem exists in the Fragments you use as tabs, I think. They seem to not show anything when they are resumed (see Fragment lifecycle). The "weird" issue that only the currently selected +/-1 tab is empty, is because the offScreenPageLimit of your ViewPager is 1 by default. All tabs above this threshold are re-created.
Therefore, increasing the value will -- in your case -- cause all your tabs to appear empty after resuming. Check in your Fragment code which lifecycle methods you use to inflate your layout, set adapters and so forth, because that's what's causing your trouble.
I guess this happens because while loading fragment android loads current and current+1, if you debug you would not see onPause getting called for the immediate next fragment.
You can reload content programmatically in onTabChanged() method of TabHost.OnTabChangeListener.
After doing much research, this worked for me.
I have a complex layout with 3 tabs in a fragment, that gets switched out for other fragments. I realized that the ViewpagerAdapter will retain state, even if you press the home button. My problem was switching back and forth would null out the child fragment UI view elements and crash. The key is to not new out your ViewPagerAdapter. Adding the null check for the Adapter worked for me. Also, be sure to allocate setOffscreenPageLimit() for your needs. Also, from what I understand setRetainInstance(true); should not be used for fragments that have UI, it is designed for headless fragments.
In the fragment that holds your Tabs:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_tab, container, false);
tabLayout = (TabLayout) view.findViewById(R.id.tablayout);
viewPager = (ViewPager) view.findViewById(R.id.viewPager);
//Important!!! Do not fire the existing adapter!!
if (viewPagerAdapter == null) {
viewPagerAdapter = new ViewPagerAdapter(getChildFragmentManager());
viewPagerAdapter.addFragments(new AFragment(), "A");
viewPagerAdapter.addFragments(new BFragment(), "B");
viewPagerAdapter.addFragments(new CFragment(), "C");
}
//Allocate retention buffers for three tabs, mandatory
viewPager.setOffscreenPageLimit(3);
tabLayout.setupWithViewPager(viewPager);
viewPager.setAdapter(viewPagerAdapter);
return view;
}
Or more simply when navigating back to tabbedfragment (assuming you use an intent and the fragment is within an activity) use:
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
This keeps the original activity and moves it to the top of the stack rather than recreating it, thus you never need to recreate the viewPager.