Develop Reference

Handle Fragment Backstack According to the Current Fragment

Problem 1
I have a Navigation Drawer and most of my fragment transactions happens from here.
So say I have 4 Items in my drawer and I am doing the transaction from all of them. So if I am at the fragment [A] and now I click on the fragment [B], I need to come back to the previous fragment i.e. [A]. But if I keep clicking on the Item B of the navigation drawer that opens the fragment [B], I keep adding it to the backstack and when I press the back button, I am still at the same fragment.
Problem 2
How do I achieve the Clear Top behavior that is used for the intents for the fragments. As intents have the power to clear the activities from the stack from the top only, I want to achieve the same behavior.

Problem 1 & 2 solution Idea:
Create an Interface say FragmentInstanceHandler
public interface FragmentInstanceHandler {
public void openFragment(Fragment fragment, String fragmentTag);
}
Create a BaseFragment like below and extend this to all your Fragment classes:
public BaseFragment extends Fragment {
public FragmentInstanceHandler fragmentInstanceHandler;
public void setFragmentInstanceHandler(FragmentInstanceHandler fragmentInstanceHandler) {
this.fragmentInstanceHandler = fragmentInstanceHandler;
}
}
Implement the FragmentInstanceHandler interface to the Activity in which you are going to open all the Fragments. Let's say Activity is MainActivity:
public MainActivity extends Activity implements FragmentInstanceHandler {
private BaseFragment currentFragment;
#Override
public void openFragment(BaseFragment fragment, String fragmentTag) {
FragmentManager fragmentManager = getSupportFragmentManager();
Fragment oldFragmentInstance = fragmentManager .findFragmentByTag(fragmentTag);
boolean fragmentPopped = fragmentManager.popBackStackImmediate (fragmentTag, 0);
if (!fragmentPopped && oldFragmentInstance == null) {
fragment.setFragmentInstanceHandler(this);
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.add(R.id.container, fragment, fragmentTag);
fragmentTransaction.addToBackStack(fragmentTag);
fragmentTransaction.commit();
currentFragment = fragment;
} else if(fragmentPopped ){
currentFragment = oldFragmentInstance;
}
if(mDrawerLayout!= null)
mDrawerLayout.closeDrawers();
}
}
Now whenever you want to open a new Fragment even from any other Fragment you can call method like below, It is advised to provide new tag if you want to have new instance of same Fragment:
fragmentInstanceHandler.openFragment(new MyFragment(), "FragmentNewInstance");
You can tweak FragmentInstanceHandlerto add your own method to replace the current Fragment instead of adding. Above solution just gives you an idea how you can acheive your solution by putting and mananging all your code from one place.

Manage Title with Fragment Stack Changed

I am using Fragment activity and a number of fragments to get added and poped out on back press.
Supposed I am adding Fragment B from Fragment A. The title of action bar that I set in A changes by navigating to B; but it is not restoring to A when I pop the fragment B out of the fragment stack as onResume of fragment is not being called.
I am using the code:
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().add(R.id.container, fragmentToReplace, tag).addToBackStack(tag).commit();
and to pop out the last fragment:
fragmentManager.popBackStack();
How to manage this. Please suggest.

You can use onBackStackChanged listener which will be called whenever a fragment is popped back. To add the listener use this:
getFragmentManager().addOnBackStackChangedListener(this);
In Override function, check the fragment which is popped and according to it you can change the actionbar title:
#Override
public void onBackStackChanged() {
//Check the fragment from the FrameLayout Container R.id.container
// Depending on the Fragment you can change the Title
setTitle("xyz");
}

Create new class in your package and extend with Fragment says TestFragment and create abstract method in it
abstract public String getTitle();
than extend your every fragment with TestFragment and override getTitle() in your fragments.
public String getTitle(){
return "YOUR_FRAGMENT_NAME";
}
getSupportFragmentManager().addOnBackStackChangedListener(
new OnBackStackChangedListener() {
#Override
public void onBackStackChanged() {
Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.content_frame);
this.setTitle(fragment.getTitle());
}
});

Passing data between fragments contained in an activity

I have an activity A with 3 fragments. Each fragments replaces each other, hence at a given time only 1 is visible.
HomeFragment has 2 textviews wrapped inside 2 cardviews. Each cardview represents a text value which comes from Fragment1 and Fragment2. When I click on say Card1,I get to the Fragment1.
Fragment1 has some cardviews, when I selects any of them I navigate back to HomeFragment and update the cardview text based on my selection in Fragment1.Here is the switch statement, depending upon what card user selects I put that in a bundle and pass it to HomeFragment.
switch (v.getId()) {
case R.id.card_view0:
Fragment1Bundle.putString("Test", "Testing");
bundle.putBundle("Fragment1Bundle", Fragment1Bundle);
fragmentTransaction.setCustomAnimations(R.anim.slideup, R.anim.slidedown, R.anim.slideup, R.anim.slidedown);
fragmentTransaction.replace(R.id.content_frame, fragment);
fragment.setArguments(bundle);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
break;
Fragment2 has same behavior as Fragment 1.
switch (v.getId()) {
case R.id.card_view0:
Fragment2Bundle.putString("Test2", "Tetsing");
bundle.putBundle("Fragment2Bundle", Fragment2Bundle);
fragmentTransaction.setCustomAnimations(R.anim.slideup, R.anim.slidedown, R.anim.slideup, R.anim.slidedown);
fragmentTransaction.replace(R.id.content_frame, fragment);
fragment.setArguments(bundle);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
break;
My challenge is that I am using bundles to pass data between fragments, My home fragment gets updated with the data it from fragment1 but when I go to fragment 2 and after making the selection come back to Home fragment, my fragment1 data is set to default. This is what I am doing in Home Fragments onCreateView()
try {
bundle1 = getArguments().getBundle("Fragment1Bundle");
bundle2 = getArguments().getBundle("Fragment2Bundle");
tv.setText(bundle1.getString("Test") == null ? null : bundle1.getString("Test"));
tv2.setText(bundle2.getString("Test2") == null ? nul : bundle2.getString("Test2"));
} catch (NullPointerException e) {
Log.d(TAG, e.printStackTrace());
}
I know that I am creating a new Homefragment in my fragment transaction in both fragment1 and fragment2, How can I keep just 1 instance of Home fragment around.

Another design recommended by Google is to use the main Activity and 2 fragments (in your case Fragment1 and Fragment2). I can see your problem of passing data bundle to HomeFragment. This suggested design uses MainActivity which is declared static (may be required for scoping issue). And it uses an interface to be established between Activity and a Fragment. I think the interface is easier than passing bundle back to the HomeFragment.
A Google webpage is # Communicating with Other Fragments. This is not just my opinion. A good SO link, I think, is How to pass data between fragments.
Code snippet from the webpage...
An example of Fragment to Activity communication:
public class HeadlinesFragment extends ListFragment {
OnHeadlineSelectedListener mCallback;
// Container Activity must implement this interface
public interface OnHeadlineSelectedListener {
public void onArticleSelected(int position);
}
...
An example of Activity to Fragment communication:
public static class MainActivity extends Activity
implements HeadlinesFragment.OnHeadlineSelectedListener{
...
public void onArticleSelected(int position) {
// The user selected the headline of an article from the HeadlinesFragment
// Do something here to display that article
}
}
Note:
OnHeadlineSelectedListener is the interface created by the Fragment.
The created method onArticleSelected has a parameter position, which comes from the ListView in ListFragment (in the sample).
You can still set data bundles and send data between Activity and Fragment. However I have not sent back data from Fragment to Activity. I normally use Fragment to handle much of UI updates.

how to pass values from activity to already open fragment and update array-list help me please. when I using interface the array-list size is zero what I do? do not us bundle method.
public class Main2Activity extends AppCompatActivity{
String desc = "data";
OnDataPassedListener onDataPassedListener;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
String passedArg = getIntent().getExtras().getString("id");
Log.d("data",passedArg);
Scription scription = new Scription();
onDataPassedListener = (OnDataPassedListener)scription;
onDataPassedListener.onDataPassed(passedArg,desc);
}
public interface OnDataPassedListener {
void onDataPassed(String text,String name);
}
}
public class Test extends Fragment implements
Main2Activity.OnDataPassedListener{
.
.
.
.
#Override
public void onDataPassed(String text,String name) {
monthlylists.get(Integer.valueOf(text)).setFood_type(name);
}

Fragment calling fragments loosing state on screen rotation

Hi i created a project with a default "Navigation Drawer Activity".
So i have a MainActivity with a fragment with is replaced for each item on menu.
One of the menus is "Customers" with shows a list of customers.
From customers fragment i can see the Interests of this customers, with is a Fragment(CustomerListFragment) calling the interests(InterestsListFragment).
There is even more levels, but to be short that's enough.
This is the code on MainActivity that i use to call fragment from fragment and pass data between
public void passData(Object[] data, Fragment f) {
Bundle args = new Bundle();
args.putSerializable("PASSED_DATA", data);
f.setArguments(args);
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, f)
.addToBackStack("")
.commit();
}
And i use like :
mCallbacks.passData(new Object[]{c}, new OpportunityListFragment());
The problem is that when i rotate the phone does not matter from wich level of activity i have, it comes back to the first fragment called(CustomerListFragment), and if i click "Back" on cellphone it gets back to where i was when i rotate the phone.
What do i have to do, to avoid this kind of problem? why it gets back to the first activity evoked if i am replacing fragments?

The answer from ste-fu is correct but let's explore programmatically. There is a good working code in Google documentation # Handling Runtime Changes. There are 2 code snippets that you have to do.
1) Code snippet:
public class MyActivity extends Activity {
private RetainedFragment dataFragment;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// find the retained fragment on activity restarts
FragmentManager fm = getFragmentManager();
dataFragment = (DataFragment) fm.findFragmentByTag(“data”);
// create the fragment and data the first time
if (dataFragment == null) {
Note: Code uses FragmentManager to find the current Fragment. If fragment is null, then the UI or app has not been executed. if not null, then you can get data from RetainedFragment object.
2) Need to retain the Fragment state.
public class RetainedFragment extends Fragment {
// data object we want to retain
private MyDataObject data;
// this method is only called once for this fragment
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// retain this fragment
setRetainInstance(true);
}
Note: setRetainInstance is used in OnCreate. And subclassing the Fragment is recommended, naming it RetainedFragment, used on snippet 1.

When you change screen orientation your parent Activity is destroyed and recreated. Unless you persist the level structure in some fashion, it will always appear as when you first started the activity. You can either use the bundle object, or for more complicated objects you need to persist it to a database.
Either way, onSaveInstanceState is your friend. Then in your onCreate method you need to check the bundle or database, and the set the fragment accordingly.

How to save an Activity's Fragment's transactional states?

Related Question.
I put together a simple app that goes like this:
Activity -> FirstFragment
Activity: onCreate() -> createFirstFragment()
FirstFragment firstFragment = (FirstFragment) getSupportFragmentManager().findFragmentByTag(FirstFragment.TAG);
if (firstFragment == null)
{
firstFragment = FirstFragment.newInstance();
getSupportFragmentManager()
.beginTransaction()
.add(R.id.firstFragmentContainer, firstFragment, FirstFragment.TAG)
.hide(firstFragment)
//.addToBackStack(null)
.commit();
}
Plain and simple, during onCreate() add and hide a fragment so that I can do show/hide animations later.
Now, my question is this: why does the Activity/FragmentManager not remember this transaction (regardless of whether I .addToBackStack() or setRetainInstance(true) on the fragment) when the activity is killed and recreated? You can test this by checking the Do not keep activities developer option. Start the app, firstFragment is hidden as expected, minimize and come back, and viola! firstFragment is there for all the world to see!
I would expect that this sort of thing would be managed by Android, or do I need to specifically record all my transactions and repeat them when the app is recreated?
Any help/advice would be greatly appreciated!
Edit: Also see related logged bug

Use FragmentStatePagerAdapter like below in your main activity. This internally calls 'onSaveInstanceState' of the fragments and hence keeps the track of the changes you made and retains the transactional states
class MyAdapter extends FragmentStatePagerAdapter {
public MyAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
// your code here
}
#Override
public int getCount() {
// returns no. of fragments count. in my case it is 4
return 4;
}
onCreate() in mainactivity generally looks like this:
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView (R.layout.scrollabletabs_main);
viewPager = (ViewPager) findViewById (R.id.pager);
FragmentManager fragManager = getSupportFragmentManager();
viewPager.setAdapter(new MyAdapter(fragManager));
}
From
http://developer.android.com/training/basics/fragments/fragment-ui.html it is mentioned that,
Note: When you remove or replace a fragment and add the transaction to the back stack, the fragment that is removed is stopped (not destroyed). If the user navigates back to restore the fragment, it restarts. If you do not add the transaction to the back stack, then the fragment is destroyed when removed or replaced.