Develop Reference

addToBackStack Not working

I am trying to close the fragment and wants to resume the main activity by using the addToBackStack in my fragment implimentation but it is not working. Back button is closing the application.
The fragment implimentation method that I am using is,
private void dispaySelectedScreen(int id) {
Fragment fragment = null;
switch (id) {
case R.id.facebook_login:
fragment = new FacebookLogin();
break;
case R.id.memes:
fragment = new Memes();
break;
case R.id.submit_image:
fragment = new SubmitImage();
break;
case R.id.discussion:
fragment = new Discussions();
break;
case R.id.invite:
fragment = new Invite();
break;
case R.id.connect_fb:
fragment = new FacebookConnect();
break;
case R.id.connect_twitter:
fragment = new TwitterConnect();
break;
case R.id.connect_instagram:
fragment = new InstaConnect();
break;
}
if (fragment != null) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.content_main, fragment);
ft.addToBackStack(null);
ft.commit();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
I have also declared one onBackPressed method for the drawer,
#Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
Please suggest..

fragment.addToBackStack(null) is enough to open the previous activity but if you want to handle some action on back pressed apart from removing the fragment then we override onBackPressed(), so this is my tested approach, kindly have a look:-
Below is my implementation:-
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getSupportFragmentManager().beginTransaction().replace(R.id.fragment_holder, new MyFragment(), "MY_FRAG")
.addToBackStack(null).commit();
}
#Override
public void onBackPressed() {
MyFragment fragment = (MyFragment) getSupportFragmentManager().findFragmentByTag("MY_FRAG");
if (fragment != null) {
if (fragment.isVisible()) {
//todo perform any action if you want when fragment is removed
}
} else {
super.onBackPressed();
}
}

I see you are using replace on transaction in that way your fragment will pop up from stack but it will reload i.e onCreateView() of that fragment will be called . Just replace
ft.replace(R.id.content_main, fragment);
to
ft.add(R.id.content_main, fragment);
For handling back button use following code .
public void onBackPressed() {
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
if (getSupportFragmentManager().getBackStackEntryCount() == 0) {
//that means your stack is empty and you want to close activity
finish();
} else {
// pop the backstack here
getSupportFragmentManager().popBackStackImmediate();
}
}
}

how only keep one instance for each fragment if i navigate many time between this fragment

for Ex.
I have bottom navigation have 4 tab
when I navigate from A-->B then B-->A then A-->B then B-->A
THEN press back ---> B - A - B - A
What I want remove this duplicate so if I press back should be B - A then exit app
public class MainActivity extends BaseActivity implements BottomNavigation.OnMenuItemSelectionListener {
private BottomNavigation mBottomNavigation;
private List<Integer> openedTabs = new ArrayList<>();
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initializeViewComponents();
}
private void initializeViewComponents() {
mBottomNavigation = (BottomNavigation) findViewById(R.id.BottomNavigation);
if (null != mBottomNavigation) {
if (openedTabs.size() == 0) {
openedTabs.add(0);
}
mBottomNavigation.setDefaultSelectedIndex(0);
mBottomNavigation.setOnMenuItemClickListener(this);
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_my_contacts, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.menu_contacts_search) {
}
return false;
}
#Override
public void onBackPressed() {
super.onBackPressed();
if (openedTabs.size() > 0) {
int lastIndex = openedTabs.size() - 1;
int beforeTheCurrent = lastIndex - 1;
if (beforeTheCurrent >= 0) {
mBottomNavigation.setSelectedIndex(openedTabs.get(beforeTheCurrent), true);
printLog("OnBackPressed", "Size: " + openedTabs.size() + " ---> LastIndex: " + lastIndex + " ---> Current: " + openedTabs.get(lastIndex) + "Go To: " + openedTabs.get(beforeTheCurrent));
openedTabs.remove(lastIndex);
}
}
}
#Override
public void onMenuItemSelect(#IdRes int i, int i1) {
openedTabs.add(i1);
switch (i) {
case R.id.profile:
printLog("Item", "profile");
replaceFragment(new ProfileFragment());
break;
case R.id.my_contacts:
printLog("Item", "my_contacts");
replaceFragment(new MyContactsFragment());
break;
case R.id.requests:
printLog("Item", "requests");
replaceFragment(new RequestsFragment());
break;
case R.id.settings:
printLog("Item", "settings");
replaceFragment(new SettingsFragment());
break;
}
}
#Override
public void onMenuItemReselect(#IdRes int i, int i1) {
}
private void replaceFragment(Fragment fragment) {
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
transaction.replace(R.id.fragmentContainer,fragment);
transaction.addToBackStack(null);
transaction.commit();
}
}

You are adding the transaction to the backStack always, so is normal that if you press the button back you get back through the whole navigation the user did.
Maybe you could try to add the transaction to the backStack transaction.addToBackStack(null); only if there aren't the same fragment on it:
fragmentManager.findFragmentByTag(TAG).
To use this, you have to assign a different Tag to every DIFFERENT fragment you are replacing:
So, try this:
private void replaceFragment(Fragment fragment, String tag) {
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
transaction.replace(R.id.fragmentContainer,fragment);
if (fragmentManager.findFragmentByTag(tag) == null)
transaction.addToBackStack(null);
transaction.commit();
And you call this function that way:
switch (i) {
case R.id.profile:
printLog("Item", "profile");
replaceFragment(new ProfileFragment(), "profile");
break;
case R.id.my_contacts:
printLog("Item", "my_contacts");
replaceFragment(new MyContactsFragment(), "my_contacts");
break;
case R.id.requests:
printLog("Item", "requests");
replaceFragment(new RequestsFragment(), "requests");
break;
case R.id.settings:
printLog("Item", "settings");
replaceFragment(new SettingsFragment(), "settings");
break;
}

You actually create a new instance in your onMenuItemSelect(..), and add everyone to backstack. So either remove your addtoBackStack(null) if this fragment-type already exists (so it doesnt get multiple times added to backstack) OR avoid creating new instances everytime the user switches between the tabs, e.g. by saving the fragments in an
Fragment[] myfrags = new Fragment[4]; //4 means count of your different fragments)
or a HashMap with your IdRes as key and the Fragment as Value

Backstack android fragment navigation

This is how I used navigation drawer to display Fragments:
private void displayView(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
switch (position) {
case 0:
fragment = new Fragment0();
break;
case 1:
fragment = new Fragment1();
break;
case 2:
fragment = new Fragment2();
break;
case 3:
fragment = new Fragment3();
break;
case 4:
fragment = new Fragment4();
break;
case 5:
fragment = new Fragment5();
}
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.frame_container, fragment)
.addToBackStack(null)
.commit();
// update selected item and title, then close the drawer
mDrawerList.setItemChecked(position, true);
mDrawerList.setSelection(position);
setTitle(navMenuTitles[position]);
mDrawerLayout.closeDrawer(drawerll);
} else {
// error in creating fragment
Log.e("MainActivity", "Error in creating fragment");
}
}
Suppose if the user navigates to Fragment 2-> Fragment 5-> Fragment3.
If the user clicks the back button I need to have the descending order and on each fragment I am displaying the name of the Fragment when he goes to that particular fragment ie:
Fragment 3-> Fragment 5-> Fragment2.
This is what I have tried:
First Method:
FragmentManager fm = getSupportFragmentManager();
int count = fm.getBackStackEntryCount();
for(int i = 0; i < count; ++i) {
fm.popBackStackImmediate();
}
Second Method:
fragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
I'm unable to get this working**(ie.. I'm unable to move it back to the fragment where I have come from**) and unable to display the name of the fragment based on the backstack
Any help is greatly appreciated.

Your navigation is working fine I guess and the issue you are facing is the tittle for which you can use
public class SampleFragment extends Fragment{
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Creating view correspoding to the fragment
View v = inflater.inflate(R.layout.fragment_layout, container, false);
// Updating the action bar title
getActivity().getActionBar().setTitle("Screen name");
return v;
}
}
in every fragment. And whenever you backpress the onCreateView method of fragmemt(the one which is poping from the backstack) gets called and the tittle will again set replacing the old tittle.

1. Handle back
You can use getSupportFragmentManager().popBackStack() method in onBackPressed:
#Override
public void onBackPressed() {
if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
getSupportFragmentManager().popBackStack();
getSupportFragmentManager().beginTransaction().commit();
}
else {
super.onBackPressed();
}
}
Don't forget to add the fragment in BackStack like :
transaction.addToBackStack(null);
2. Display Name
To show the current fragment name in actionbar, you can get it on onResume of your Fragment :
#Override
protected void onResume() {
super.onResume();
((FrgmentActivtiyName)getActivity).changeTitle("title");
}
Define a method which set the title in the actionbar in your FrgmentActivity:
public void changeTitle(String titleToSet) {
// set title as titleToSet
}
Hope it helps ツ

Please try this:
In the activity which holds the fragments, override the onbackPressed() method by,
#Override
public void onBackPressed() {
if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
getSupportFragmentManager().popBackStack();
getSupportFragmentManager().beginTransaction().commit();
}
else {
super.onBackPressed();
}
}

if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.frame_container, fragment).commit();
menuList.setItemChecked(position, true);
menuList.setSelection(position);
}

How to keep only one instance of a fragment, when switching with NavigationDrawer?

My App starts with a AddressFragment. From the NavigationDrawer I start (amongst others) a new AddressFragment with:
getSupportFragmentManager().beginTransaction()
.replace(R.id.container, new AddressFragment())
.addToBackStack(null)
.commit();
But I would rather just go back the first instance. How could I do that?
Or more general, how can I find out, whether an instance of a fragment already exists and then start that, if yes, otherwise create one?

When creating the fragment set a tag for it, then later you can find it through the fragment manager and replace/create accordingly.
FragmentManager fManager = getFragmentManager();
FragmentTransaction fTransaction = fManager.beginTransaction();
Fragment fragment = fManager.findFragmentByTag("uniqueTag");
// If fragment doesn't exist yet, create one
if (fragment == null) {
fTransaction.add(R.id.fragment_list, new ListFrag(), "uniqueTag");
}
else { // re-use the old fragment
fTransaction.replace(R.id.fragment_list, fragment, "uniqueTag");
}

Step one:
Optimize current code to allow a Fragment to have his own "TAG"
getSupportFragmentManager().beginTransaction()
.replace(R.id.container, new AddressFragment())
.addToBackStack(**AddressFragment.class.getName()**)
.commit();
Step two:
Somewhere in your application flow you will need to determine if a fragment exists:
public static boolean isFragmentInBackstack(final FragmentManager fragmentManager, final String fragmentTagName) {
for (int entry = 0; entry < fragmentManager.getBackStackEntryCount(); entry++) {
if (fragmentTagName.equals(fragmentManager.getBackStackEntryAt(entry).getName())) {
return true;
}
}
return false;
}
Step three:
perform fragment action
if (exists) {
// Fragment exists, go back to that fragment
//// you can also use POP_BACK_STACK_INCLUSIVE flag, depending on flow
mFragmentManager.popBackStackImmediate(AddressFragment.class.getName(), 0);
} else {
// Fragment doesn't exist
// STEP 1 + additional backstack management
}

This is tested answer, Hope this will help you
First Make these field globally in MainActivity
private static final int TIME_INTERVAL = 2000;
private long mBackPressed;
private FragmentManager fm;
private FragmentTransaction ft;
private DrawerLayout drawer;
Now in onNavigationItemSelected() implement like that
#Override
public boolean onNavigationItemSelected(MenuItem item) {
Fragment fragment = null;
Class fragmentClass = null;
switch (item.getItemId()) {
case R.id.nav_home:
fragmentClass = Fragment.class;//this is MainAvctivty extends AppCompatActivity
break;
case R.id.nav_f1:
fragmentClass = FragmentOne.class;
break;
case R.id.nav_f2:
fragmentClass = FragmentTwo.class;
break;
case R.id.nav_f3:
fragmentClass = FragmentThree.class;
break;
case R.id.nav_f4:
fragmentClass = FragmentFour.class;
break;
case R.id.nav_f5:
fragmentClass = FragmentFive.class;
break;
default:
fragmentClass = Fragment.class;
}
try {
fragment = (Fragment) fragmentClass.newInstance();
} catch (Exception e) {e.printStackTrace();}
//Insert the fragment by replacing any existing fragment
fm = getSupportFragmentManager();
ft = fm.beginTransaction();
ft.replace(R.id.frame_container, fragment);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
ft.addToBackStack(null);
ft.commit();
item.setChecked(true);
setTitle(item.getTitle());
drawer.closeDrawers();
return true;
}
Now handle onbackpressed like below
#Override
public void onBackPressed() {
if (drawer != null) {
fm = getSupportFragmentManager();
ft = fm.beginTransaction();
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else if (fm.getBackStackEntryCount() > 0) {
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_CLOSE);
ft.commit();
} else if (mBackPressed + TIME_INTERVAL > System.currentTimeMillis()) {
super.onBackPressed();
} else {
Toast.makeText(this,"Press again to exit the app",Toast.LENGTH_SHORT).show();
}
mBackPressed = System.currentTimeMillis();
}
}

First time you create the fragment with a tag.
When you want to replace it try to get the fragment with tag and if it return null you create a new one

How can I assure that a View is available when I call a Fragment method?

I'm using the native Android drawer for my menu, here in MainActivity :
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
switch (position) {
case 0:
//Home
fragment = new EntryFragment();
break;
case 1:
//Journal
fragment = new JournalFragment();
break;
case 2:
// Medications
fragment = new RxFragment();
break;
case 3:
// Reminders
fragment = new ReminderFragment();
break;
case 4:
// Counselor Locator
fragment = new LocatorFragment();
break;
case 5:
// Library
fragment = new LibraryFragment();
break;
case 6:
// Settings
break;
case 7:
// About
break;
default:
break;
}
if (fragment != null) {
fm.beginTransaction()
.replace(R.id.container, fragment).addToBackStack(String.valueOf(position)).commit();
String fragmentTitles[] = getResources().getStringArray(R.array.menu_array);
if(mActionBar != null) {
mActionBar.setTitle(fragmentTitles[position]);
}
} else {
Log.e("MainActivity", "Error in creating fragment");
}
But I'm repurposing EntryFragment for another activity (EntryDetailActivity), so in EntryFragment I defined a couple of methods to modify the view based on which activity is hosting it:
// Runs on the home page, shows/hides appropriate views
public void prepareForHomeView() {
mTxtDate.setVisibility(View.GONE);
mBtnDiffDay.setVisibility(View.GONE);
mEdtNotes.setVisibility(View.GONE);
mBtnSave.setVisibility(View.GONE);
mBtnDelete.setVisibility(View.GONE);
}
// Runs on the detail page, shows/hides appropriate views
public void prepareForDetailView() {
mBtnLog.setVisibility(View.GONE);
}
In EntryDetailActivity, I can easily call prepareForDetailView() in onResumeFragments(), but I'm having an issue of where to call prepareForHome() in MainActivity, since I am swapping fragments in and out based on the menu. Any suggestions?
/** Update **/
I assigned the fragments a tag that is the position of the menu through addToBackstack(). I also added the following method to my MainActivity:
#Override
public void onAttachFragment(Fragment fragment) {
super.onAttachFragment(fragment);
FragmentManager fm = getSupportFragmentManager();
EntryFragment entryFrag = (EntryFragment)fm.findFragmentByTag("0");
if(entryFrag != null) {
Log.v("rx", "Home frag is not null");
} else {
Log.v("rx", "Home frag is null");
}
}

Activity (or FragmentActivity) has onAttachFragment(Fragment fragment) - you could do an instanceof on fragment to determine if it is the correct type of fragment (or use the id, tag, etc) and call the appropriate method.
Alternatively, you could have the Fragment check the getActivity() (in onCreateView / onViewCreated).