Develop Reference

Hide/show fragments in single ViewPager window

How can I hide SearchFragment and display ChatFragment, without remove() in ViewPager? I had no issues with creating new instance everytime, but I don't want onDestroy() to have place, since i will be switching these 2 views very frequently. I want to create them once and have the ability to show/hide one for another.
My code is making two views to be seen in fragment_search(id cointainer)at once, then just crashes.
I was thinking about creating both Fragments at start, and then just manipulate them by attach and detach, but I can't really figure this out since ViewPager doesn't make it easier
public Fragment getItem(int position) {
switch (position) {
case 0:
if (fragment1 == null)
{
fragment1 = SearchFragment.newInstance(new SearchFragment.MyListener() {
#Override
public void onChatFound() {
// Dont want to remove fragment, just hide this view || fm.beginTransaction().remove(fragment1).commit();
Fragment chatTag = fm.findFragmentByTag("ChatTag");
if (chatTag == null)
{
chatFragment = ChatFragment.newInstance();
fm.beginTransaction().add(R.id.fragment_search, chatFragment, "ChatTag").commit();
}
fragment1 = chatTag;
notifyDataSetChanged();
}
});
}
return fragment1;

Prevent fragment from recreating every time bottomnavigation tab is clicked

I'm using BottomNavigationView in android to make a application just like Instagram. I'm using fragments with the navigationTabs. App have 5 tabs initialy I've set the middle tab as active tab and loads it once the app start. when i click on any other tab a network call is made and data is loaded. Now when i press on back button or click on the last tab again(which was loaded on startup) the fragment is recreated and the network call is made to load the same data. I want to show the previous fragments with same data without recreating.
I've tried using
transaction.add(container,fragment);
but to no avail.
my code on tab click
if (item.getItemId() == R.id.nav_OverView && _current != R.id.nav_OverView) {
Overview _overView = new Overview();
_fragmentTransaction.hide(_currentFragment);
_fragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_CLOSE);
_fragmentTransaction.add(R.id.content_base_drawer, _overView);
_fragmentTransaction.commit();
_current = R.id.nav_OverView;
viewIsAtHome = true;
}
I know using remove and add is same as using replace.
Any help is appreciated.

Before creating the view you can check if the view is already created or not, the below code helps fragment recreating problem.
View view;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState)
{
if (view == null)
{
view = inflater.inflate(R.layout.frag_layout, container, false);
init(view);
}
return view;
}

Make _overview into a class field (instead of a local variable), and change your listener code to this:
Also, use replace instead of hide+add, this will prevent Fragment already added errors.
Replace an existing fragment that was added to a container. This is
essentially the same as calling remove(Fragment) for all currently
added fragments that were added with the same containerViewId and then
add(int, Fragment, String) with the same arguments given here.
See example:
if (item.getItemId() == R.id.nav_OverView && _current != R.id.nav_OverView) {
if (_overView == null) {
_overView = new Overview();
}
_fragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_CLOSE);
_fragmentTransaction.replace(R.id.content_base_drawer, _overView);
_fragmentTransaction.commit();
_current = R.id.nav_OverView;
viewIsAtHome = true;
}

communication flow between fragments and activity

I'm trying to make a simple reminder app. When creating a new reminder I have the following setup:
MainEditActivity.java: 2 placeholder FrameLayouts for the following fragments:
EditNameFragment.java
custom Action Bar (Cancel, OK button)
EditText for the reminder name
CheckBox to toggle one of the following fragments
EditDateFragment.java OR EditLocationFragment.java (both have a lot of views)
MainEditActivity.java:
private LocationFragment mLocationFragment;
private DateFragment mDateFragment;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_new_remainer_main); // 2 frame layouts
if (savedInstanceState == null) {
Fragment newFragment = new NewReminderFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(R.id.reminder_title_fragment, newFragment).commit();
mDateFragment = new DateFragment();
ft = getFragmentManager().beginTransaction();
ft.add(R.id.date_or_location_fragment, mDateFragment).commit();
}
}
public void onCheckBoxClick(View view)
{
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
if(mLocationFragment == null)
mLocationFragment = new LocationFragment();
CheckBox checkBox = (CheckBox)findViewById(R.id.checkBoxID);
if(checkBox != null)
{
if(checkBox.isChecked()) {
fragmentTransaction.replace(R.id.date_or_location_fragment, mLocationFragment);
} else {
fragmentTransaction.replace(R.id.date_or_location_fragment, mDateFragment);
}
fragmentTransaction.commit();
}
#Override
public void handleEvent(EventInfo event) {
// here I get all the data (name, data, time, location, etc)
}
EditNameFragment.java:
private EventHandler mEventHandler;
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
mEventHandler = (EventHandler)activity;
}
View doneButton = actionBarButtons.findViewById(R.id.doneBtnTextID);
doneButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
createNewReminder();
}
});
private void createNewReminder()
{
// Event info object to store all information (reminder name, data, time, etc)
EventInfo eventInfo = new EventInfo();
// access either Date or Location Fragment (depending on which is visible)
// FIXME: access the fragments and get the data
// let the activity know to display the new reminder
mEventHandler.handleEvent(eventInfo);
}
Question: I started off using only 1 MainActivity with all elements and a ViewFlipper. Then I read that fragments are better to eventually adjust to tablets better. Is this the right way to lay this out?
Question: I know how to get the data from EditNameFragment.java. But how do I get the data that the user entered from EditDataFragment or EditLocationFragment?
Do I need an instance of those two Fragments in the MainActivity to access their Views? Or do I need another callback like I did with EventHandler? If yes, would the rule be to have a callback for each fragment?
I guess I'm struggling a bit with the communication flow between those components. And I know fragment to fragment communication isn't a good design

Fragments are self-contained, modular components that would make sense if presented by themselves independently of the other. The canonical example is a list of newspaper articles and the display for an article...both could be presented either independently or separately and it would make sense. In your case, I think having multiple fragments is probably unnecessary because they do not make sense independently of the other (or you would end up with a half-defined event). It seems as if you have one fragment to edit the date and one fragment to edit the name, but conceptually, the two fragments really edit one "object," which is the event. Thus, this should probably be done within one fragment with a ViewFlipper.
Have you seen this?
http://developer.android.com/training/basics/fragments/communicating.html
You need instances of all three fragments in the main activity, and you need to define interfaces for each fragment and implement them in the main activity.

Fragment gets initialized twice when reloading activity with tabs when orientation changes

I have a problem reloading an activity with tabs and fragments when I change the orientation of my device.
Here's the situation:
I have an activity which has 3 tabs in the action bar. Each tab loads a different fragment in a FrameLayout in main view. Everything works fine if I don't change the orientation of the device. But when I do that Android tries to initialize the currently selected fragment twice which produce the following error:
E/AndroidRuntime(2022): Caused by: android.view.InflateException: Binary XML file line #39: Error inflating class fragment
Here's the sequence of steps that produce the error:
I load the activity, select tab nr 2. and change the orientation of the device.
Android destroys the activity and the instance of the fragment loaded by tab nr 2 (from now on, 'Fragment 2'). Then it proceeds to create new instances of the activity and the fragment.
Inside Activity.onCreate() I add the first tab to the action bar. When I do that, this tab gets automatically selected. It may represent a problem in the future, but I don't mind about that now. onTabSelected gets called and a new instance of the first fragment is created and loaded (see code below).
I add all the other tabs without any event being triggered, which is fine.
I call ActionBar.selectTab(myTab) to select Tab nr 2.
onTabUnselected() gets called for the first tab, and then onTabSelected() for the second tab. This sequence replaces the current fragment for an instance of Fragment 2 (see code below).
Next, Fragment.onCreateView() is called on Fragment 2 instance and the fragment layout gets inflated.
Here is the problem. Android Calls onCreate() and then onCreateView() on the fragment instance ONCE AGAIN, which produces the exception when I try to inflate (a second time) the layout.
Obviously the problem is Android is initializing the fragment twice, but I don't know why.
I tried NOT selecting the second tab when I reaload the activity but the second fragment gets initialized anyway and it is not shown (since I didn't select its tab).
I found this question: Android Fragments recreated on orientation change
The user asks basically the same I do, but I don't like the chosen answer (it's only a workaroud). There must be some way to get this working without the android:configChanges trick.
In case it's not clear, what I want to know how whether to prevent the recreation of the fragment or to avoid the double initialization of it. It would be nice to know why is this happening also. :P
Here is the relevant code:
public class MyActivity extends Activity implements ActionBar.TabListener {
private static final String TAG_FRAGMENT_1 = "frag1";
private static final String TAG_FRAGMENT_2 = "frag2";
private static final String TAG_FRAGMENT_3 = "frag3";
Fragment frag1;
Fragment frag2;
Fragment frag3;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// my_layout contains a FragmentLayout inside
setContentView(R.layout.my_layout);
// Get a reference to the fragments created automatically by Android
// when reloading the activity
FragmentManager fm = getFragmentManager();
this.frag1 = fm.findFragmentByTag(MyActivity.TAG_FRAGMENT_1);
this.frag2 = fm.findFragmentByTag(MyActivity.TAG_FRAGMENT_2);
this.frag3 = fm.findFragmentByTag(MyActivity.TAG_FRAGMENT_3)
ActionBar actionBar = getActionBar();
// snip...
// This triggers onTabSelected for the first tab
actionBar.addTab(actionBar.newTab()
.setText("Tab1").setTabListener(this)
.setTag(MyActivity.TAG_FRAGMENT_1));
actionBar.addTab(actionBar.newTab()
.setText("Tab2").setTabListener(this)
.setTag(MyActivity.TAG_FRAGMENT_2));
actionBar.addTab(actionBar.newTab()
.setText("Tab3").setTabListener(this)
.setTag(MyActivity.TAG_FRAGMENT_3));
Tab t = null;
// here I get a reference to the tab that must be selected
// snip...
// This triggers onTabUnselected/onTabSelected
ab.selectTab(t);
}
#Override
protected void onDestroy() {
// Not sure if this is necessary
this.frag1 = null;
this.frag2 = null;
this.frag3 = null;
super.onDestroy();
}
#Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
Fragment curFrag = getFragmentInstanceForTag(tab.getTag().toString());
if (curFrag == null) {
curFrag = createFragmentInstanceForTag(tab.getTag().toString());
if(curFrag == null) {
// snip...
return;
}
}
ft.replace(R.id.fragment_container, curFrag, tab.getTag().toString());
}
#Override
public void onTabUnselected(Tab tab, FragmentTransaction ft)
{
Fragment curFrag = getFragmentInstanceForTag(tab.getTag().toString());
if (curFrag == null) {
// snip...
return;
}
ft.remove(curFrag);
}
private Fragment getFragmentInstanceForTag(String tag)
{
// Returns this.frag1, this.frag2 or this.frag3
// depending on which tag was passed as parameter
}
private Fragment createFragmentInstanceForTag(String tag)
{
// Returns a new instance of the fragment requested by tag
// and assigns it to this.frag1, this.frag2 or this.frag3
}
}
The code for the Fragment is irrelevant, it just returns an inflated view on onCreateView() method override.

I got a simple answer for that:
Just add setRetainInstance(true); to the Fragment's onAttach(Activity activity) or onActivityCreated(Bundle savedInstanceState).
These two are call-backs in the Fragment Class.
So basically, what setRetainInstance(true) does is:
It maintains the state of your fragment as it is, when it goes through:
onPause();
onStop();
It maintains the instance of the Fragment no matter what the Activity goes through.
The problem with it could be, if there are too many Fragments, it may put a strain on the System.
Hope it helps.
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
setRetainInstance(true);
}
Open for Correction as always. Regards, Edward Quixote.

It seems that, when the screen is rotated and the app restarted, it is recreating each Fragment by calling the default constructor for the Fragment's class.

I have encountered the same issue and used the following workaround:
in the fragment's onCreateView begining of:
if (mView != null) {
// Log.w(TAG, "Fragment initialized again");
((ViewGroup) mView.getParent()).removeView(mView);
return mView;
}
// normal onCreateView
mView = inflater.inflate(R.layout...)

I think this is a fool proof way to avoid re-inflating of the root view of the fragment:
private WeakReference<View> mRootView;
private LayoutInflater mInflater;
/**
* inflate the fragment layout , or use a previous one if already stored <br/>
* WARNING: do not use in any function other than onCreateView
* */
private View inflateRootView() {
View rootView = mRootView == null ? null : mRootView.get();
if (rootView != null) {
final ViewParent parent = rootView.getParent();
if (parent != null && parent instanceof ViewGroup)
((ViewGroup) parent).removeView(rootView);
return rootView;
}
rootView = mFadingHelper.createView(mInflater);
mRootView = new WeakReference<View>(rootView);
return rootView;
}
#Override
public View onCreateView(final LayoutInflater inflater, final ViewGroup container, final Bundle savedInstanceState) {
mInflater=inflater!=null?inflater:LayoutInflater.from(getActivity());
final View view = inflateRootView();
... //update your data on the views if needed
}

add
android:configChanges="orientation|screenSize"
in the manifest file

To protect activity recreate try to add configChanges in your Activity tag (in manifest), like:
android:configChanges="keyboardHidden|orientation|screenSize"

My code was a little different, but I believe our problem is the same.
In the onTabSelected I didn't use replace, I use add when is the first time creating the fragment and attach if isn't. In the onTabUnselected I use detach.
The problem is that when the view is destroyed, my Fragment was attached to the FragmentManager and never destroyed. To solve that I implemented on the onSaveInstanceBundle to detach the fragment from the FragmentManager.
The code was something like that:
FragmentTransition ft = getSupportFragmentManager().begin();
ft.detach(myFragment);
ft.commit();
In the first try I put that code in the onDestroy, but I get a exception telling me that I couldn't do it after the onSaveInstanceBundle, so I moved the code to the onSaveInstanceBundle and everything worked.
Sorry but the place where I work don't allow me to put the code here on StackOverflow. This is what I remember from the code. Feel free to edit the answer to add the code.

I think you are facing what I faced. I had a thread downloader for json which starts in onCreate() , each time I changed the orientation the thread is called and download is fired. I fixed this using onSaveInstance() and onRestoreInstance() to pass the json response in a list, in combination of checking if the list is not empty, so the extra download is not needed.
I hope this gives you a hint.

I solved this problem by using below code.
private void loadFragment(){
LogUtil.l(TAG,"loadFragment",true);
fm = getSupportFragmentManager();
Fragment hf = fm.findFragmentByTag("HOME");
Fragment sf = fm.findFragmentByTag("SETTING");
if(hf==null) {
homeFragment = getHomeFragment();// new HomeFragment();
settingsFragment = getSettingsFragment();// new Fragment();
fm.beginTransaction().add(R.id.fm_place, settingsFragment, "SETTING").hide(settingsFragment).commit();
fm.beginTransaction().add(R.id.fm_place, homeFragment, "HOME").commit();
activeFragment = homeFragment;
}else{
homeFragment = hf;
settingsFragment = sf;
activeFragment = sf;
}
}
Initiate this method in OnCreate();

How to test if a fragment view is visible to the user?

I have a ViewPager, each page is a Fragment view. I want to test if a fragment is in a visible region. the Fragment.isVisible only test
the fragment is attached to a activity
the fragment is set to visible
the fragment has been added to a view
The ViewPager will create 3 (by default) fragment and all three of them meet the above criteria, but only one is actually visible to the user (the human eyes)

This is what I use to determine the visibility of a fragment.
private static boolean m_iAmVisible;
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
m_iAmVisible = isVisibleToUser;
if (m_iAmVisible) {
Log.d(localTAG, "this fragment is now visible");
} else {
Log.d(localTAG, "this fragment is now invisible");
}
}

You're right there is a better way to do this!
Have a look at the FragmentPagerAdapter javadoc online and you'll see there is a method setPrimaryItem(ViewGroup container, int position, Object object):void doing exactly what you need.
From the javadoc
public void setPrimaryItem (ViewGroup container, int position, Object object)
Called to inform the adapter of which item is currently considered to
be the "primary", that is the one show to the user as the current
page.
Parameters container The containing View from which the page will be
removed. position The page position that is now the primary.
object The same object that was returned by instantiateItem(View,
int).
Note on scroll state
Now if you implement this and start debugging to get a feel of when exactly this is called you'll quickly notice this is triggered several times on preparing the fragment and while the user is swiping along.
So it might be a good idea to also attach a ViewPager.OnPageChangeListener and only do what has to be done once the viewpagers scroll state becomes SCOLL_STATE_IDLE again.

For my purposes, it worked to use ViewPager.OnPageChangeListener.onPageSelected() in conjunction with Fragment.onActivityCreated() to perform an action when the Fragment is visible. Fragment.getUserVisibleHint() helps too.

I'm using "setMenuVisibility"-Method for resolving this Problem. As every Fragment can have actionbar-items this is the part where you can determine which Fragment is currently visible to the user.
#Override
public void setMenuVisibility(final boolean visible) {
super.setMenuVisibility(visible);
if (!visible) {
//not visible anymore
}else{
yay visible to the user
}
}

What is wrong with using getView().isShown() to find out if a Fragment is actually visible?

isVisible()
Can still return true even if the fragment is behind an activity.
I'm using the following:
if (getView() != null && getView().isShown()) {
//your code here
}

If you know what "page" each fragment is attached to you could use ViewPager.getCurrentItem() to determine which fragment is "visible".

In my case i a have to do some work on the first fragment when the fragment is visible to the user
#Override
public void onWindowFocusChanged(boolean hasFocus) {
super.onWindowFocusChanged(hasFocus);
if(viewPager.getAdapter() instanceof YourPager)
{
Fragment fragemnt=((YourPager)viewPager.getAdapter()).getFragment(0); //getFragment(int index) custom method
if( fragemnt instanceof YourFragment)
{
((YourFragment)fragemnt).methodWhochShouldBeCalledAfterUIVisible();
}
}
}

setUserVisibleHint probably may not be called, onHiddenChanged may be called not every time when another fragment is being closed. So, you may rely on onResume (and onPause), but it is usually called too often (for example, when you turn on a device screen). Also in some situations it is not called, you should manage current fragment in host activity and write:
if (currentFragment != null) {
currentFragment.onResume();
}

Kotlin:
if (userVisibleHint) {
// the fragment is visible
} else {
// the fragment is not visible
}
Java
if (getUserVisibleHint()) {
// the fragment is visible
} else {
// the fragment is not visible
}
https://developer.android.com/reference/android/app/Fragment.html#getUserVisibleHint()
https://stackoverflow.com/a/12523627/2069407