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ViewPager2 not working properly with Fragments and click events

I just wanna know if I'm doing something wrong since I'm kinda new to all this.
If there is anything else that you'll like me to add just let me know.
This is the repo branch where I'm trying to implement the ViewPager if you wanna see all the code.
Context
So I have 4 Categories represented with Fragments, each of this categories holds an ArrayList of items that each has a onItemClickListener that should reproduce some audio.
I'm trying to display the Fragments with a ViewPager but the problem is that when I scroll from a Fragment to another, then come back to the already created Fragment, it doesnt register the touch event, nothing happens, not even an error nor exception.
If I go to a newly created Fragment the touch works just fine.
Also, after switching back to an already created Fragment if I scroll even just a little bit to another Fragment and comeback or through the ArrayList of that Fragment for some reason it starts to recognize the touch in the ArrayList items again.
Similar questions that didn't really help
Fragments in ViewPager2 does not respond to clicks if scroll position is 0
ViewPager2 conflicting with SwipeRefreshLayout
Android ViewPager2 with fragment containing a recyclerview not scrolling
What I've tried
I tried to use a coordinatorlayout wrapping the ViewPager2 but there is no difference
I've been reading some of the official viewPager2 examples that are written in Kotlin but none of them seem to have a similar situation (also it's hard for me to read Kotlin code)
Code Snippets
word_list.xml:
<ListView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/root_list_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/tan_background" />
activity_main.xml:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="MainActivity">
<androidx.viewpager2.widget.ViewPager2
android:id="#+id/viewpager"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"/>
</FrameLayout>
This is one of the Fragments, the other three are basically the same, just the items in the arrayList change and some other minor things:
// ...Skipped some irrelevant code...
public class NumbersFragment extends Fragment {
private ArrayList<Word> mWords;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.word_list, container, false);
mWords = new ArrayList<>();
// ...Add all the items to the list...
// Make the adapter for the word items
WordAdapter adapter = new WordAdapter(getActivity(), mWords, R.color.category_numbers);
// Find the root view of the list
ListView listView = rootView.findViewById(R.id.root_list_view);
// Add adapter to the root list view
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Log.d("NumbersFragment", "CLICKED");
}
}
});
return rootView;
}
#Override
public void onPause() {
super.onPause();
Log.d("NumbersFragment", "Fragment paused");
}
}
This is the Category adapter, it manages the fragments:
public class CategoryAdapter extends FragmentStateAdapter {
private static final int NUM_CATEGORIES = 4;
// Required public constructor
public CategoryAdapter(#NonNull FragmentActivity fragmentActivity) {
super(fragmentActivity);
}
#NonNull
#Override
public Fragment createFragment(int position) {
// Depending on which page the user is in,
// create a fragment of the corresponding category
switch (position) {
case 0:
return new NumbersFragment();
case 1:
return new FamilyFragment();
case 2:
return new ColorsFragment();
default:
return new PhrasesFragment();
}
}
#Override
public int getItemCount() {
return NUM_CATEGORIES;
}
}
And this is my MainActivity:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Set the content of the activity to use the activity_main.xml layout file
setContentView(R.layout.activity_main);
// Find the view pager that will allow the user to swipe between fragments
ViewPager2 viewPager = findViewById(R.id.viewpager);
// Create an adapter that knows which fragment should be shown on each page
CategoryAdapter adapter = new CategoryAdapter(this);
//or CategoryAdapter adapter = new CategoryAdapter(getSupportFragmentManager(), getLifecycle());
// Set the adapter into the view pager
viewPager.setAdapter(adapter);
}
}

add this in your MainActivity viewPager.setOffscreenPageLimit(3); after creating viewpager
It’s because the ViewPager has a default offscreen limit of 1 ,and ViewPager2 has a default offscreen limit of 0.
In ViewPager2 when you switch tabs the previous tab will be automatically refreshed.
in ViewPager if you have 3 tabs or more when you switch to 3rd tab automatically first one will be destroyed and when you goes to 1st tab it will be recreated.
viewPager.setOffscreenPageLimit(3); from this line when you switch to a tab,the previous 3 tabs will be preloaded and next 3 tabs will be preloaded so nothing will be refreshed.

ListView of a Fragment (of a ViewPager inside a Fragment) that implements LoaderCallbacks<Cursor> is empty when I return back to it

The ListView inside of a Fragment that contains a ViewPager is empty when I return back to it. This ViewPager is inside of a Fragment because I'm using a Navigation Drawer Layout. I'll try to explain it in more details now:
I am using a Navigation Drawer layout and, consequently, using Fragments. In the main activity, in onCreate, I set the current Fragment with these lines of code:
#Override
protected void onCreate(Bundle savedInstanceState) {
/* More code */
currentFragment = new MainFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.layout_for_fragments, currentFragment).commit();
}
The MainFragment class contains a ViewPager that is initialized with these lines of code in the onCreateView():
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
/* More code */
ViewPager viewPager = (ViewPager) rootView.findViewById(R.id.main_view_pager);
viewPager.setAdapter(new SimpleFragmentPagerAdapter(getActivity(), getActivity().getSupportFragmentManager()));
/* Code for Tablayout */
return rootView;
}
One of the Fragments of the SimpleFragmentPagerAdapter class is this one that implements LoaderManager.LoaderCallbacks
public class ExpensesFragment extends Fragment implements LoaderManager.LoaderCallbacks<Cursor> {
private ExpenseCursorAdapter mExpenseCursorAdapter;
private static final int EXPENSE_LOADER = 1;
public ExpensesFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_expenses, container, false);
ListView expensesListView = (ListView) rootView.findViewById(R.id.expenses_list_view);
mExpenseCursorAdapter = new ExpenseCursorAdapter(getContext(), null);
expensesListView.setAdapter(mExpenseCursorAdapter);
getLoaderManager().initLoader(EXPENSE_LOADER, null, this);
return rootView;
}
#Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
return new CursorLoader(/* arguments */);
}
#Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
mExpenseCursorAdapter.swapCursor(data);
}
#Override
public void onLoaderReset(Loader<Cursor> loader) {
mExpenseCursorAdapter.swapCursor(null);
}
}
On the first run, everything works fine. However, if I click on the navigation drawer menu, which I'm implementing this way, the ListView becomes empty:
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
int id = item.getItemId();
if (id == R.id.nav_main) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().remove(currentFragment).commit();
currentFragment = new MainFragment();
fragmentManager.beginTransaction().replace(R.id.layout_for_fragments, currentFragment).commit();
} else if (id == R.id.nav_blank) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().remove(currentFragment).commit();
currentFragment = new BlankFragment();
fragmentManager.beginTransaction().replace(R.id.layout_for_fragments, currentFragment).commit();
}
drawer.closeDrawer(GravityCompat.START);
return true;
}
The problem also exists when I rotate the device. There is a difference though. When I use the Navigation Drawer menu, none of the methods of the LoaderManager.LoaderCallbacks are called, but when I rotate the device, onLoadFinished is called.
Anyway, the problem persists. Any ideias how to solve it?
Thanks in advance.

I have found the solution!
Basically, I made two mistakes.
The first one is about the rotation of the device.
When the device is rotated, the Activity is destroyed and onCreate is called again. In this case, I should't call new MainFragment(). So, I check if the savedInstanceState is null before I call it, like this:
if (savedInstanceState == null) {
currentFragment = new MainFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().
replace(R.id.layout_for_fragments, currentFragment).commit();
}
The second one is about a fragment within a fragment. In this case, I can't simply call getSupportFragmentManager(). I should call getChildFragmentManager() instead and that's it!

Why is accessing TextView of a Fragment inside Activity throwing an error

MainActivity class:
/* all necessary imports */
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
/* Other variable initialized here... */
FragOne fo;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
fo.setTextViewText("This is added from Activity");
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.addDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
viewPager = (ViewPager) findViewById(R.id.viewpager);
setupViewPager(viewPager);
tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(viewPager);
}
private void setupViewPager(ViewPager viewPager) {
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(new FragOne(), "My Tracker");
adapter.addFragment(new FragTwo(), "Team Tracker");
viewPager.setAdapter(adapter);
}
class ViewPagerAdapter extends FragmentPagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
#Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
#Override
public int getCount() {
return mFragmentList.size();
}
public void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
#Override
public CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
}
#Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
#SuppressWarnings("StatementWithEmptyBody")
#Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_manage) {
} else if (id == R.id.nav_share) {
} else if (id == R.id.nav_send) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
Fragment class:
/* all necessary imports */
public class FragOne extends Fragment {
TextView tvCName;
public FragOne() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_frag_one, container, false);
return view;
//return inflater.inflate(R.layout.fragment_frag_one, container, false);
}
#Override
public void onViewCreated(View view , Bundle savedInstanceState) {
tvCName = (TextView) view.findViewById(R.id.tvctq);
}
public void setTextViewText(String value){
tvCName.setText(value);
}
}
Fragment XML Layout:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.mytip.FragOne">
<TextView
android:text="TextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/tvctq" />
</FrameLayout>
I am trying to access the TextView inside the Fragment from MainActivity like this:
FragOne fo;
fo.setTextViewText("This is added from Activity");
I keep getting a NullPointerExceptionError. I looked at all the articles to see how to access, however none of them helped me.
Can someone please let me know what am I doing wrong and how to fix it?
I also plan on adding other Views inside my Fragment that I would need to access in the future.

Because fo hasn't been initialized in the following code snippet:
FragOne fo;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
fo.setTextViewText("This is added from Activity");
...
}
fo.setTextViewText() reasonably throws NPE.

You have to pay attention to the Activity lifecycle - you seem to be setting everything up correctly, but making a few mistakes accessing the correct instance of the fragment at the time it's actually ready. Things you should do
Get proper instance of the fragment from your ViewPager, like #ginomempin suggested;
Only try to set your text no earlier then your activities onStart method has been called - I usually do it onResume method (you can override it if you haven't already). Doing it in onResume method in the activity makes sure your Fragment has already gone through it's lifecycle up till onResume as well, and data will refresh if it has been brought to the background previously.
Here's a lifecycle diagram for your reference:

You need to use your Fragment factory method when creating your Fragment in your activity. Please see below:
**
Back Stack
**
The transaction in which fragments are modified can be placed on an internal back-stack of the owning activity. When the user presses back in the activity, any transactions on the back stack are popped off before the activity itself is finished.
For example, consider this simple fragment that is instantiated with an integer argument and displays that in a TextView in its UI:
public static class CountingFragment extends Fragment {
int mNum;
/**
* Create a new instance of CountingFragment, providing "num"
* as an argument.
*/
static CountingFragment newInstance(int num) {
CountingFragment f = new CountingFragment();
// Supply num input as an argument.
Bundle args = new Bundle();
args.putInt("num", num);
f.setArguments(args);
return f;
}
/**
* When creating, retrieve this instance's number from its arguments.
*/
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mNum = getArguments() != null ? getArguments().getInt("num") : 1;
}
/**
* The Fragment's UI is just a simple text view showing its
* instance number.
*/
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.hello_world, container, false);
View tv = v.findViewById(R.id.text);
((TextView)tv).setText("Fragment #" + mNum);
tv.setBackgroundDrawable(getResources().getDrawable(android.R.drawable.gallery_thumb));
return v;
}
}
A function that creates a new instance of the fragment, replacing whatever current fragment instance is being shown and pushing that change on to the back stack could be written as:
void addFragmentToStack() {
mStackLevel++;
// Instantiate a new fragment.
Fragment newFragment = CountingFragment.newInstance(mStackLevel);
// Add the fragment to the activity, pushing this transaction
// on to the back stack.
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.simple_fragment, newFragment);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
ft.addToBackStack(null);
ft.commit();
}
After each call to this function, a new entry is on the stack, and pressing back will pop it to return the user to whatever previous state the activity UI was in.
Source: https://developer.android.com/reference/android/app/Fragment.html

You need to get the same instance of FragOne from the viewpager.
First, you can only access the FragOne instance after the ViewPager is setup.
Then, try this:
fo = adapter.getItem(0)
Note:
Since you already have fragments, it would be better to let the fragment itself handle the UI-related actions (such as setting the textview) rather than from the Activity.

android-on navigation drawer item click get data from database and populate another list

My application contains a Navigation Drawer and i use its list items as a menu, by clicking on which help in retrieving data from database and populating my listview in main activity...
I want to send a query to a database function based on the item clicks of drawer list and based on the query result my another list view in main activity will be populated..
Basically what i tried till now is assigning a different string holding the query based on the item click into the String type variable "query" and passing it as a parameter to a function of database who processes it as a rawQuery and retrieves result...
Due to some errors which am not able to detect it is throwing Null Pointer Exception...
Following is the code for MainActivity.java
public class MainActivity extends ActionBarActivity
implements NavigationDrawerFragment.NavigationDrawerCallbacks {
private NavigationDrawerFragment mNavigationDrawerFragment;
private CharSequence mTitle;
private Cursor c;
public MyDatabaseHandler dbOpen;
private String query;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mNavigationDrawerFragment =
(NavigationDrawFragment)
getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
mTitle = getTitle();
mNavigationDrawerFragment.setUp(
R.id.navigation_drawer,
(DrawerLayout) findViewById(R.id.drawer_layout));
dbOpen = new MyDatabaseHandler(this);
c = dbOpen.getListContent(query);
ListView lv = (ListView) findViewById(R.id.list);
lv.setAdapter(new SimpleCursorAdapter(this,R.layout.topic_list_each_row,
c,new String[]{MyDatabaseHandler.KEY_UTOPICNAME,MyDatabaseHandler.KEY_UNAME },
new int[] {R.id.topicname,R.id.unitname} ,0));
}
#Override
public void onNavigationDrawerItemSelected(int position) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
.commit();
}
//here where i have thought of passing string into query variable
public void onSectionAttached(int number) {
switch (number) {
case 1:
query = "SELECT * FROM cosmtable ORDER BY utopicname";
break;
...............
..............
}}
public void restoreActionBar() {
ActionBar actionBar = getSupportActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
actionBar.setDisplayShowTitleEnabled(true);
actionBar.setTitle(mTitle);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
if (!mNavigationDrawerFragment.isDrawerOpen()) {
// Only show items in the action bar relevant to this screen
// if the drawer is not showing. Otherwise, let the drawer
// decide what to show in the action bar.
getMenuInflater().inflate(R.menu.main, menu);
restoreActionBar();
return true;
}
return super.onCreateOptionsMenu(menu);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
/**
* 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 PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public PlaceholderFragment() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
((MainActivity) activity).onSectionAttached(
getArguments().getInt(ARG_SECTION_NUMBER));}}}
The activity_main file is-
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.pockettutsforcosm.MainActivity" >
<FrameLayout
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<ListView
android:id="#+id/list"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:dividerHeight="10dp">
</ListView>
</LinearLayout>
<fragment
android:id="#+id/navigation_drawer"
android:name="com.example.pockettutsforcosm.NavigationDrawerFragment"
android:layout_width="#dimen/navigation_drawer_width"
android:layout_height="match_parent"
android:layout_gravity="start"
tools:layout="#layout/fragment_navigation_drawer" />
</android.support.v4.widget.DrawerLayout>
Please help me out in finding a way to achieve the results..
If further details needed then please let me know..
Thank You
UPDATE
One thing i Figured out in this is i was trying to write the query at wrong place i.e., the query variable shouldn't be assigned with a value at onAttach event...
SO i changed the code in Main Activity as follows-
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
//FragmentManager fragmentManager = getSupportFragmentManager();
//fragmentManager.beginTransaction()
// .replace(R.id.container, PlaceholderFragment.newInstance(position))
// .commit();
try
{
switch(position)
{
case 0:
query = "SELECT * FROM cosmtable ORDER BY topic_name";
c = dbOpen.getListContent(query);
ListView lv = (ListView) findViewById(R.id.list);
lv.setAdapter(new SimpleCursorAdapter(this,R.layout.topic_list_each_row,c,
new String[]{MyDatabasehandler.KEY_UTOPICNAME,MyDatabaseHandler.KEY_UNAME},
new int[] {R.id.topicname,R.id.unitname} ,0));
break;
.............................................
}
}
catch (Exception e) {
Log.e("error on fragment", "creating the mainScreen");
}
finally {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, PlaceholderFragment.newInstance(position + 1 ))
.commit();}}
And after doing this the content to be loaded from first item click of navigation drawer doesn't appears when the application is first launched....
it appears only when the item is clicked...
i want it to appear on application launch...
Do i need to create separate methods in my database handler class to return separate query results for each switch case??

Basically what i did is i created a separate function which can manipulate the query string accordingly the position of each element of navigation drawer and then it is being passed to get cursor data function in database handler and then the query results being back thrown to the simple cursor adapter in MainActivity....
The other thing is did for the problem of blank screen when the application is launched is i called the same function which manipulating the database query for the first element...
This is giving me my desired outputs..
Still if there is another good to go method out there then i am open to know that approach too.
for till now i will accept this as a answer..

Change fragment visibility in runtime when the fragment was created using FragmentPagerAdapter

I'm trying to create my first Android app that looks like following: there is main activity with multiple fragments initialized by FragmentPagerAdapter. There is another activity (SettingsActivity) where I want to list all the fragment names and allow hiding some of them. To hide them I want to use the following:
FragmentManager fm=getFragmentManager();
Fragment myFragment=fm.findFragmentByTag("tag");
fm.beginTransaction().hide(myFragment).commit();
The problem is that I don't know fragment id or tag, not sure if they exist. How I can get them? Should I switch to XML definition to make it possible?
Adapter:
public class TabsPagerAdapter extends FragmentPagerAdapter {
public TabsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int index) {
switch (index){
case 0:
return new CoverFragment();
case 1:
return new NumbersConverterFragment();
case 2:
return new TempConverterFragment();
case 3:
return new LengthConverterFragment();
case 4:
return new AreaConverterFragment();
case 5:
return new VolumeConverterFragment();
case 6:
return new WeightConverterFragment();
case 7:
return new SpeedConverterFragment();
}
return null;
}
#Override
public int getCount() {
return 8;
}
Main activity:
public class MainActivity extends FragmentActivity implements ActionBar.TabListener {
private ViewPager viewPager;
private TabsPagerAdapter tabsPagerAdapter;
private ActionBar actionBar;
#Override
protected void onCreate(Bundle savedInstanceState) {
String[] tabs={getString(R.string.title_section0), getString(R.string.title_section1),getString(R.string.title_section2)};
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager=(ViewPager) findViewById(R.id.pager);
actionBar=getActionBar();
tabsPagerAdapter=new TabsPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(tabsPagerAdapter);
actionBar.setHomeButtonEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
for(String tab : tabs){
actionBar.addTab(actionBar.newTab().setText(tab).setTabListener(this));
}
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageSelected(int position) {
// on changing the page
// make respected tab selected
actionBar.setSelectedNavigationItem(position);
}
...
});
}
Fragment layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#fbfdfb"
>
<TextView android:text="#string/celsius_" android:id="#+id/textView1"
android:layout_width="wrap_content" android:layout_height="wrap_content"></TextView>
<EditText android:text="" android:id="#+id/txtCelsius" android:layout_width="match_parent"
android:layout_height="wrap_content"></EditText>
<TextView android:text="#string/fahrenheit_" android:id="#+id/textView1"
android:layout_width="wrap_content" android:layout_height="wrap_content"></TextView>
<EditText android:text="" android:id="#+id/txtFahrenheit" android:layout_width="match_parent"
android:layout_height="wrap_content"></EditText>
<TextView android:text="#string/kelvin_" android:id="#+id/textView1"
android:layout_width="wrap_content" android:layout_height="wrap_content"></TextView>
<EditText android:text="" android:id="#+id/txtKelvin" android:layout_width="match_parent"
android:layout_height="wrap_content"></EditText>
</LinearLayout>
Fragment class:
public class TempConverterFragment extends Fragment {
EditText txtCelsius, txtFahrenheit, txtKelvin;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.temp_converter_fragment, container, false);
txtCelsius = (EditText) rootView.findViewById(R.id.txtCelsius);
txtFahrenheit = (EditText) rootView.findViewById(R.id.txtFahrenheit);
txtKelvin = (EditText) rootView.findViewById(R.id.txtKelvin);
...
}
...
}
Thanks in advance.

If SettingsActivity is not the Activity holding the FragmentPagerAdapter, then you would have to re-create all the fragments. The nature of a fragment is to be closely tied to it's activity.
If SettingsActivity is the Activity holding the FragmentPagerAdapter, then As I recall, FragmentPagerAdapter will initialize all the 8 fragments as soon as possible to have them ready when you swipe, unlike FragmentStatePagerAdapter. This means that you should (I think) be able to create each fragment in the constructor TabsPagerAdapter and keeping a reference to them, which you could access using getter methods on the TabsPagerAdapter.
Here is an example of how to get easy access to your pageradapter fragments:
public class DisplayPagerAdapter extends FragmentStatePagerAdapter {
private static final String TAG = "DisplayPagerAdapter";
SparseArray<DisplayFragment> registeredFragments = new SparseArray<DisplayFragment>();
#Inject DisplayCoreModule display;
public DisplayPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public int getCount() {
return (display != null && display.getPagesCount() > 0) ? display.getPagesCount() : 1;
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
#Override
public Fragment getItem(int position) {
Log.d(TAG, "getItem " + position);
return DisplayFragment.newInstance(position);
}
#Override
public CharSequence getPageTitle(int position) {
if (display != null && display.getPagesCount() > 0) {
return "Side " + (position+1);
} else {
return super.getPageTitle(position);
}
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Log.d(TAG, "instantiateItem " + position);
DisplayFragment fragment = (DisplayFragment) super.instantiateItem(container, position);
registeredFragments.put(position, fragment);
return fragment;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
Log.d(TAG, "destroyItem " + position);
registeredFragments.remove(position);
super.destroyItem(container, position, object);
}
public Fragment getRegisteredFragment(int position) {
return registeredFragments.get(position);
}
public SparseArray<DisplayFragment> getRegisteredFragments() {
return registeredFragments;
}
}
Now if you implement this usage of registeredFragments , you can call tabsPagerAdapter.getRegisteredFragment(2) to get your TempConverterFragment.
SparseArray<DisplayFragment> should be SparseArray<Fragment> in your case
Now this does not solve the your SettingsActivity problem. But if I understand you correctly, then adding the fragments your want directly in the layout XML of SettingsActivity would make sense. Then it would be easy to temporarily hide the fragments or whatever using:
FragmentManager fm=getFragmentManager();
Fragment myFragment=fm.findFragmentById(R.id.frag_tempconverter)
fm.beginTransaction().hide(myFragment).commit();
Notice the use of findFragmentById. The tag is usually used for dynamically added fragments (atleast in my mind). The findFragmentById will surely return a fragment if it is defined in the XML layout but just to be clear, it will be a new instance of the fragment.
To address your questions:
What if I move the fragments to the main activity XML? Won't it make things simpler
Do not think so, the updated answer shows how to easily access the fragments (from within your main activity).
Though not sure I can use FragmentManager in SettingsActivity
Sure you can. You can add new fragments, access available fragments (from predefined XML using findById or dynamically added using findByTag). You cannot, however, access the same instance of the fragment as was kept by your main activity.
To share information between the fragments and the two activities, you need to persist the state of your fragments somehow (which is a different topic).
All in all I think you are on the right path, you just need to combine the right pieces of the puzzle :)