Develop Reference

Exiting from Activity with only fragments

My app contains one empty activity and a couple of fragments. The onCreate of the activity replaces the empty view in activity_main.xml with a MainFragment that contains some buttons. Each button launches a separate fragment, and user can navigate from one fragment to another, etc.
On the press of back key, the current fragment correctly gets replaced with the previous fragment, until you get to the MainFragment. When user presses back from MainFragment, it hides the main fragment and you see the white empty background of the main activity. But I want to exit from the activity at this point, as that would be the sensible behaviour.
I am able to achieve this by calling super.onBackPressed() for a second time from onBackPressed if there are no fragments left in the fragment manager.
#Override
public void onBackPressed() {
super.onBackPressed();
FragmentManager manager = getSupportFragmentManager();
List<Fragment> fragments = manager.getFragments();
if (fragments == null || fragments.size() == 0) {
Log.d(TAG, "No more fragments: exit");
super.onBackPressed();
}
}
Is this acceptable thing to do - would it create any issues in the activity workflow? Is there a better/standard way to handle this scenario?

There is no problem to do that, but probably it would be easier if when you add the main fragment to the activity you do NOT call .addToBackStack()

You don't really need to override onBackPressed in your Activity. I would suggest implementing a method for adding fragments in your Activity:
protected void addFragment(Fragment fragment, boolean addToBackStack) {
String tag = fragment.getClass().getName(); //It's optional, may be null
FragmentTransaction transaction = getSupportFragmentManager()
.beginTransaction()
.add(R.id.your_container_id, fragment, tag);
if (addToBackStack) {
transaction.addToBackStack(tag);
}
transaction.commit();
}
And modify your onCreate method of activity like in the following snippet:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
// Add your fragment only if it is a first launch,
// otherwise it will be restored by system
addFragment(new YourFirstFragment(), false);
}
}
For all other fragments use:
addFragment(new OtherFragment(), true);

Saving states of multiple fragments in activity

I am working on an application and there is one specific thing that is bothering me. Let's just say I have one activity and 2 fragments.FragmentA and FragmentB and FragmentA gets attached when activity starts.
I want to save the fragment data and fragment state when orientation changes occur.I have successfully saved fragment data using OnSavedInstanceState method. Now I want to save fragment state in the activity so that if orientation change occurs I want to be on the fragment I was (in my case either FragmentA or FragmentB depends on which was showing before config changes occur).
This is how I am saving the fragment state in the Activity:
#Override
protected void onSaveInstanceState(Bundle outState) {
// Save the values you need into "outState"
super.onSaveInstanceState(outState);
outState.putLong(SS_DATE, userDate.getTime());
android.support.v4.app.FragmentManager manager = getSupportFragmentManager();
Fragment currentFragment = this.getSupportFragmentManager().findFragmentById(R.id.content_container);
manager.putFragment(outState, "currentFragment", currentFragment);
}
And this is how I am retrieving on which fragment I was when the orientation change occurred:
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
FragmentManager manager = getSupportFragmentManager();
#SuppressLint("CommitTransaction")
FragmentTransaction transaction = manager.beginTransaction();
if (savedInstanceState != null) {
Fragment MyFragment = (Fragment) manager.getFragment(savedInstanceState, "currentFragment");
if (MyFragment instanceof FragListStudentsAttendance) {
Log.v("onRestore", FragListStudentsAttendance.TAG);
}else if (MyFragment instanceof FragGetClassesForAttendance){
Log.v("onRestore", FragGetClassesForAttendance.TAG);
if(MyFragment!=null) {
mFragGetClassesForAttendance = (FragGetClassesForAttendance) MyFragment;
}else{
mFragGetClassesForAttendance = new FragGetClassesForAttendance();
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// mFragGetClassesForAttendanceNew.setRetainInstance(true);
// transaction.replace(R.id.content_ssadmin_container, mFragGetClassesForAttendanceNew, "FragGetClassesForAttendance").addToBackStack(null);
transaction.add(R.id.content_ssadmin_container, mFragGetClassesForAttendance, FragGetClassesForAttendance.TAG);
//transaction.replace(R.id.newEnrollmentMainContainer, mFragNewEnrollmentResults).addToBackStack("FragNewEnrollments");
transaction.commit();
mFragGetClassesForAttendance.setDate(userDate);
}
}
}
}
Now
Scenario 1:
If I am on fragment A and I rotate the device every thing works fine as it should. Like fragment have web services which loads the data into listview so I check if data exist then there is no need to run the web service and that working for now
Scenario 2:
If I am on fragment B and orientation change occurs everything works fine as it is supposed to be on fragment B. Now When I press back button Fragment A gets called again and all the data also comes from service. I think this shouldn't happen because it was supposed to be in BackStack and it's data was saved. So what Should I do now here?
Scenario 3: On FragmentB I have noticed that when I rotates the device the saveInstanceState function of FragmentA also gets called. Why it is so? where as I was replacing the FragmentB with FragmentA ?
Some Confusions:
Let me talk about some of the confusions also , maybe someone clear it to me although I have searched and read a lot about fragment and activity life cycle,
Actually I want to save the data per activity and fragment on device rotation. I know how to do it with activity(how to save states) so I also know how to do it in the fragment (save state of fragment views) now I am confused how to tell activity which fragment was showing and which to go after config changes(rotation) ? also what happens to FragmentA if I am on FragmentB Does its get attach and detach again and again in background?

I got your problems and confusions. I think the life cycle of fragment is confusing you. and indeed it will confuse you.
You need to learn different situations.
1. Fragment Life cycle when it is in foreground (attaching and detaching with activity) . Please keenly observe all the methods that will call i.e OnSaveInstance,onCreateView,OnDestroyView,onDestroy
2. Fragment life cycle when it is in background (observe the methods stated above)
3. Fragment life cycle when it is added to backstack (and not in foreground)
I am quite sure you are confused with the point number 3. As when the fragment is added to backstack it never gets destroy. So rotating device twice will set the ffragment data to null. I think you are restoring data on ActivityCreated or on onViewCreated ,
Ill suggest you to restore the fragment data in the oncreate. this will work for you when your fragment is coming back to foreground from the backstack .
Example
private List<String> mCountries;</pre>
#Override
public void onCreate(Bundle savedInstanceState)
{
if (savedInstanceState != null)
{
// Populate countries from bundle
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View view = inflater.inflate(R.layout.fragment_countries, container, false);
if (mCountries == null)
{
// Populate countries by calling AsyncTask
}
return view;
}
public void onSaveInstanceState(Bundle outState)
{
// Save countries into bundle
}
Hope this will clear your confusions.

Android fragment simple backstack

I have one activity containing one container that will receive 2 fragments.
Once the activity initialises i start the first fragment with:
showFragment(new FragmentA());
private void showFragment(Fragment fragment) {
getSupportFragmentManager().beginTransaction()
.replace(R.id.container, fragment, fragment.getTag())
.addToBackStack(fragment.getTag())
.commit();
}
Then when the user clicks on FragmentA, I receive this click on Activity level and I call:
showFragment(new FragmentB());
Now when I press back button it returns to fragment A (thats correct) and when i press again back button it show empty screen (but stays in the same activity). I would like it to just close the app (since the activity has no parent).
There are a lot of posts related with Fragments and backstack, but i can't find a simple solution for this. I would like to avoid the case where I have to check if im doing back press on Fragment A or Fragment B, since i might extend the number of Fragments and I will need to maintain that method.

You are getting blank screen because when you add first fragment you are calling addToBackStack() due to which you are adding a blank screen unknowingly!
now what you can do is call the following method in onBackPressed() and your problem will be solved
public void moveBack()
{
//FM=fragment manager
if (FM != null && FM.getBackStackEntryCount() > 1)
{
FM.popBackStack();
}else {
finish();
}
}
DO NOT CALL SUPER IN ONBACKPRESSED();
just call the above method!

addToBackStack(fragment.getTag())
use it for fragment B only, not for fragment A

I think your fragment A is not popped out correctly, try to use add fragment rather replace to have proper back navigation, however You can check count of back stack using:
FragmentManager fragmentManager = getSupportFragmentManager();
int count = fragmentManager.getBackStackEntryCount();
and you can also directly call finish() in activity onBackPressed() when you want your activity to close on certain fragment count.

Returning back to an Activity after calling and closing a Fragment does not change my Activity's lifecycle

Given an Activity that acts as a Home page (it never closes) that launches various fragments, how to know when the Activity is visible to the user?
From what I have observed, when I open a fragment the lifecycle for the Activity never changes, onPause() is not called. And when I close the fragment, onResume() is not called on my Activity.
Here is how I am starting my fragments, I am using this method and passing the fragment I want to launch to it.
public void addFragment(int containerId, Fragment fragment, boolean addToBackStack) {
// Check if the fragment has been added already. If so, then
// don't add the fragment.
Fragment temp = mFragmentManager.findFragmentByTag(fragment.getClass().getName());
if(temp != null && temp.isAdded()) {
return;
}
FragmentTransaction ft = mFragmentManager.beginTransaction();
ft.add(containerId, fragment, fragment.getClass().getName());
if(addToBackStack)
ft.addToBackStack(null);
ft.commit();
}
What is the methodology for indicating that my Activity is visible again? Thanks in advance!

in the oncreate method of your home activity, call
mFragmentManager.addOnBackStackChangedListener(this) ;
and then define
#Override
public void onBackStackChanged() {
int backStackCount = mFragmentManager.getBackStackEntryCount();
if(backStackCount == 0) {} //back to home screen
}

Your Activity is always Visible even if thousand Fragments are showing at the same time, for the sake of understanding Fragments are just Custom-Views, and the Fragment gives a helping hand in handling your View, so onPause() on your activity does not need to called when a Fragment dies or is born,just like inflating a View.
Just like Sir #Tim Mutton said, you need to check your BackStack to know if you are back, or you can use the ViewGroup method ViewGroup.indexOfChild(View child) - this method will an int of value getChildCount()-1 which means its on top of its fellow sibblings..
Hope it helps

How to save previous values in fragment while we switch to other fragment and return to last one

I have a fragment (say FragA) gets and another fragment (say FragB).
In FragA I set some values seekbar and put a check on checkbox
but now if click on FragB and then click on FragA then all set values are gone.
For fragments I have used a ListAdapter which set a fragment depending on position no. where I clicked. I don't want it on back button press but on clicking that fragment.
My Question is how can I restore a fragment to its previous state while setting parameter in other fragments and clicking to those fragments which I set before.

Make use of onSaveInstanceState(), below is the example how you need to implement it
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("curChoice", mCurCheckPosition);
}
And later you can use it like this:
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
if (savedInstanceState != null) {
// Restore last state for checked position.
mCurCheckPosition = savedInstanceState.getInt("curChoice", 0);
}
}
It will be a good idea if you go through fragments documentation

You can save each transaction to a back stack managed by the activity, allowing the user to navigate backward through the fragment changes (similar to navigating backward through activities).
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
Before you call commit(), however, you might want to call addToBackStack(), in order to add the transaction to a back stack of fragment transactions. This back stack is managed by the activity and allows the user to return to the previous fragment state, by pressing the Back button.
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