Develop Reference

Avoid creating the fragments again using BottomNavigationView

I am adding a BottomNavigationView with three fragments to my app.
Everything works correctly, except one thing.
In the first fragment, there is an EditText view, in the second a ListView and in the third one some texts and images loaded from a JSON hosted in the server.
This is my code:
bottomNavigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
int id = item.getItemId();
switch (id) {
case R.id.menu_dash:
fragment = new frg_dash();
break;
case R.id.menu_list:
fragment = new frg_list();
break;
case R.id.menu_info:
fragment = new frg_info();
break;
}
final FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.replace(R.id.contenedor_principal, fragment).commit();
return true;
}
});
The problem is that every time I go from one fragment to another using the bottomNavigationView buttons, the Fragment starts all its execution again.
The result I'm looking for is that if the user in the second fragment is, for example, in the middle of the ListView, it goes to the third fragment and returns again, the ListView continues where it was.
Or if you press the button of the third Fragment in the bottomNavigationView, do not load the data again from the server.
I guess the problem is that when you click on a bottomNavigationView button, the fragment is created again:
... switch (id) {
case R.id.menu_dash:
fragment = new frg_dash();
break; ...
But it's just a guess. I suppose it can be controlled with the onCreate, onActivityCreated and onCreateView methods, but again, they are just my assumptions.
I've tried it with the hide () and show () parameters of the fragments, but without success ... or I'm not applying it well
I greatly appreciate the help in advance.
EDIT
This is my example currently with all the parts related to the answer:
public void replaceFragment(Fragment fragment, #Nullable Bundle bundle, boolean popBackStack, boolean findInStack) {
Log.v("2134", "Dentro");
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
String tag = fragment.getClass().getName();
Log.v("2134", "tag:" + tag);
Fragment parentFragment;
if (findInStack && fm.findFragmentByTag(tag) != null) {
parentFragment = fm.findFragmentByTag(tag);
} else {
parentFragment = fragment;
}
// if user passes the #bundle in not null, then can be added to the fragment
if (bundle != null) {
parentFragment.setArguments(bundle);
} else {
parentFragment.setArguments(null);
}
// this is for the very first fragment not to be added into the back stack.
if (popBackStack) {
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
} else {
ft.addToBackStack(parentFragment.getClass().getName() + "");
}
ft.replace(R.id.contenedor_principal, parentFragment, tag);
ft.commit();
fm.executePendingTransactions();
}
...
bottomNavigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
int id = item.getItemId();
switch (id) {
case R.id.menu_panel:
fragment = new frg_panel();
break;
case R.id.menu_promos:
fragment = new frg_promociones();
break;
case R.id.menu_catalogo:
fragment = new frg_catalogo();
break;
}
replaceFragment(fragment, null, true, true);
return true;
}
});

Use this code to open your fragment. Your fragment will not create every time. It will get same fragment from stack if exist.
/**
* replace or add fragment to the container
*
* #param fragment pass android.support.v4.app.Fragment
* #param bundle pass your extra bundle if any
* #param popBackStack if true it will clear back stack
* #param findInStack if true it will load old fragment if found
*/
public void replaceFragment(Fragment fragment, #Nullable Bundle bundle, boolean popBackStack, boolean findInStack) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
String tag = fragment.getClass().getName();
Fragment parentFragment;
if (findInStack && fm.findFragmentByTag(tag) != null) {
parentFragment = fm.findFragmentByTag(tag);
} else {
parentFragment = fragment;
}
// if user passes the #bundle in not null, then can be added to the fragment
if (bundle != null)
parentFragment.setArguments(bundle);
else parentFragment.setArguments(null);
// this is for the very first fragment not to be added into the back stack.
if (popBackStack) {
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
} else {
ft.addToBackStack(parentFragment.getClass().getName() + "");
}
ft.replace(R.id.contenedor_principal, parentFragment, tag);
ft.commit();
fm.executePendingTransactions();
}
use it like
Update :
If your fragment is home or dashboard fragment then
Fragment f = new YourFragment();
replaceFragment(f, null, true, true);
Otherwise
Fragment f = new YourFragment();
replaceFragment(f, null, false, true);
Important This code is not replacement of saving all states or variables in fragment. This code will useful because it will not create fragment instance again.
For saving all states and variables in fragment for future use see this answer

Android fragment handling back button

I am creating an application with multiple fragments. I have four fragments fragment1, fragment2, fragment3, fragment4. I am moving from different orders like f1 -> f2 -> f4 -> f3 -> f1 or any other order. But when I click the back button from each fragment I need to go to the previous fragment. How to handle this.
Edit 1:
I already tried
FragmentManager fm = ((Activity) context).getFragmentManager();
for (int i = 0; i < fm.getBackStackEntryCount(); i++) {
fm.popBackStack();
}
Which is not help me to solve my issue.

Sample code of Manage Fragment back stack
private Stack<Fragment> stack = new Stack<Fragment>();
public void pushFragments(Fragment fragment, boolean shouldAnimate,
boolean shouldAdd) {
drawerClose = false;
if (shouldAdd)
stack.push(fragment);
this.changeFragment = fragment;
invalidateOptionsMenu();
changeFragment(fragment, shouldAnimate, false);
}
public void popFragments() {
/*
* Select the second last fragment in current tab's stack.. which will
* be shown after the fragment transaction given below
*/
Fragment fragment = stack.elementAt(stack.size() - 2);
// / pop current fragment from stack.. /
stack.pop();
/*
* We have the target fragment in hand.. Just show it.. Show a standard
* navigation animation
*/
this.changeFragment = fragment;
invalidateOptionsMenu();
changeFragment(fragment, false, true);
}
private void changeFragment(Fragment fragment, boolean shouldAnimate, boolean popAnimate) {
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction ft = manager.beginTransaction();
if (shouldAnimate)
ft.setCustomAnimations(R.anim.slide_in_right,
R.anim.slide_out_left);
if (popAnimate)
ft.setCustomAnimations(R.anim.slide_in_left,
R.anim.slide_out_right);
ft.replace(R.id.content_frame, fragment);
ft.commit();
}
//On BackPress just check this thing
private void backManage() {
if (stack.size() > 1) {
popFragments();
}
}

Use addToBackStack(String tag), while committing the fragment to add the fragment into the stack of your application:
getFragmentManager().beginTransaction().replace(fragmentContainer.getID(), fragment)
.addToBackStack(null).commit();`

on Activity
#Override
public void onBackPressed() {
if(check_if_backstack_is_null)
super.onBackPressed();
else
{
popupFromBackstack();
}
}

You should override onBackPressed method:
#Override
public void onBackPressed() {
if (fragment != null && fragment.getChildFragmentManager().getBackStackEntryCount() > 0){
fragment.getChildFragmentManager().popBackStack();
}else {
super.onBackPressed();
}
}

For this you can set addToBackStack to fragment transation and then call commit.
By calling addToBackStack(), the replace transaction is saved to the back stack so the user can reverse the transaction and bring back the previous fragment by pressing the Back button.
If you add multiple changes to the transaction (such as another add() or remove()) and call addToBackStack(), then all changes applied before you call commit() are added to the back stack as a single transaction and the Back button will reverse them all together.

You just need to add addToBackStack(null) by FragmentTransaction.
when you are calling next Fragment just add this method with null parameter.
Like this.
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(..............);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();

Use this lines of code for it:-
#Override
public void onBackPressed() {
if ( getSupportFragmentManager().getBackStackEntryCount() > 0){
fm.popBackStack();
}else {
super.onBackPressed();
}
}
To get the backStack functionality in your fragmentthan you should have use the .addToBackStack(null) , while performing the fragment transaction like below:-
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.YOUR_CONTAINER, YOUR_FRAGMENT,"TAG")
.addToBackStack(null) /// IT IS NECESSARY TO GET THE BACK STACK PROPERTY IN YOUR FRAGMENT
.commitAllowingStateLoss();

Back Navigation in Android

I am beginner in android and trying to develop an android app in which I stuck in back navigation. My issue is :
How to manage backstack with activities and fragments.
A1 activity with frag1 calls A2 activity and A2 activity displays a user list where on click of a list to check user profile, call to A1 Activity with Frag 2.
On opening of Frag2 of A1 activity, We are using intent flag: flag_activity_reorder_to_front and adding frag1 to backstack with FragmentManager transaction
Now IF I click on back then It shows A1 Activity with frag1 instead of A2 Activity.
IF I don't add frag1 into backstack then on back, It works with first back but on second back it exits from the app.
Any suggestions?

Try using single activity and handle all fragment transactions in it using an interface. Activity should implement this interface.
Example:
public interface FragChanger {
int NEXT_FRAGHELLO =1;
int NEXT_FRAGSET = 2;
int NEXT_FRAGSELECT =3;
int NEXT_FRAGLOG=4;
int NEXT_FRAGCHAT=5;
void onFragmentChange(int nextFrag);
}
The following should be in Your activity:
#Override
public void onFragmentChange(int nextFrag) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
switch (nextFrag){
case NEXT_FRAGHELLO:
break;
case NEXT_FRAGSET:
FragSet fragSet = new FragSet();
ft.replace(containerId,fragSet,"fragset");
ft.addToBackStack(null);
ft.commit();
break;
case NEXT_FRAGSELECT:
FragSelect fragSelect = new FragSelect();
ft.replace(containerId,fragSelect,"fragselect");
ft.addToBackStack(null);
ft.commit();
break;
case NEXT_FRAGCHAT:
FragChat fragChat = new FragChat();
ft.replace(containerId,fragChat,"fragchat");
ft.addToBackStack(null);
ft.commit();}
break;
case NEXT_FRAGLOG:
ft.replace(containerId,fragLog,"fraglog");
ft.addToBackStack(null);
ft.commit();
break;
}
Handling back in your activity:
#Override
public void onBackPressed() {
Log.d(TAG,"button back pressed");
//Check which fragment is displayed an do whatever you need
//for example like this
if (getSupportFragmentManager().findFragmentById(containerId) instanceof FragLog){
Fragment fl = getSupportFragmentManager().findFragmentByTag("fraglog");
if (fl !=null){
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.remove(fl);
ft.commit();
return;
}
}
}
Of course, this is only an example, but may be useful in Your case

Handling fragment backstack in Navigation drawer

okay i know there are other questions that on first glance make this one look like a duplicate, but none of these answers work in my case,
What i want is the first fragment displayed to be like a Main Activity in respect to how the back button works, i need whichever fragment i choose from my navigation drawer to go back to the first fragment when the back button is pressed then a user would quit the app by pressing it again.
So ive tried using addToBackStack and when i move to another fragment if i press the back button it comes back to my first fragment (exactly as i want) but pressing the back button again leaves me with a white screen (i wonder if this is due to the transaction animation im using which ive included below) so to get around this i tried overriding the back button and throwing in a call to finish(); but this causes whichever fragment im in to finish instead of going back to the first fragment, ive tried a handful of workarounds from the above mentioned link and many others but cannot find a decent fix any suggestions?
here is my Main Activity displayView
private void displayView(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
switch (position) {
case 0:
fragment = new FirstFragment();
break;
case 1:
fragment = new glideFrag();
break;
case 2:
fragment = new secondGlideFrag();
break;
case 3:
fragment = new thirdGlideFrag();
break;
case 4:
fragment = new forthGlideFrag();
break;
case 5:
fragment = new lgFrag();
break;
case 6:
fragment = new cyanFrag();
break;
case 7:
fragment = new sonyFrag();
break;
case 8:
fragment = new SecondFragment();
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.setCustomAnimations(R.anim.enter,R.anim.exit,R.anim.pop_enter,R.anim.pop_exit);
//fragmentManager.beginTransaction()
fragmentTransaction.replace(R.id.frame_container, fragment).addToBackStack("first Fragment").commit();
// update selected item and title, then close the drawer
mDrawerList.setItemChecked(position, true);
mDrawerList.setSelection(position);
setTitle(navMenuTitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
} else {
// error in creating fragment
Log.e("MainActivity", "Error in creating fragment");
}
i found this that looks like a great way around it
private boolean popNext = false;
if(popNext){
if(position == INITIAL_POSITION){
onBackPressed();
mDrawerLayout.closeDrawer(mDrawerList);
popNext = false;
return;
}
getSupportFragmentManager().popBackStackImmediate();
}
else{
if(position == INITIAL_POSITION){
mDrawerLayout.closeDrawer(mDrawerList);
return;
}
popNext=true;
}
but im still fairly new to android and im not sure what to set INITIAL_POSITION to, I tried
private static final INITIAL_POSITION = 0;
but without any luck

When adding the initial fragment, you must not add it to the back stack.
You must only do it for the next ones. When the back stack will be empty, the Activity will just finish.
Edit: Here is an explanation of the problem so you can figure out how to fix it:
Each time you add a fragment transaction to the back stack, you allow the user to revert it by pressing the back button and the Activity will return to the state it was before the transaction. If the initial fragment is added to the back stack, then when the user press back, the screen becomes blank, because there was nothing displayed before you added the initial fragment. That's why the initial fragment transaction which adds the first visible fragment to your Activity must not be added to the back stack. Usually you initialize the initial fragment like this:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState == null) {
Fragment fragment = new FirstFragment();
getSupportFragmentManager().beginTransaction()
.add(R.id.frame_container, fragment)
.commit();
}
}

BladeCoders answer was more trying to tell me how the backstack works rather than answering my question, i ended up not adding any fragments to the back stack, .addToBackStack(null), and overriding back button in MainActivity, feels like a little bit of a hack but works perfectly
#Override
public void onBackPressed() {
FragmentManager fragmentManager = getSupportFragmentManager();
if (fragmentManager.getBackStackEntryCount() < 1){
Fragment fragment = new FirstFragment();
FragmentTransaction fragmentTransaction =
getSupportFragmentManager().beginTransaction();
fragmentTransaction.setCustomAnimations(R.anim.enter, R.anim.exit,
R.anim.pop_enter, R.anim.pop_exit);
getSupportActionBar().setTitle(mDrawerTitle);
fragmentTransaction.replace(R.id.frame_container,
fragment).addToBackStack("first").commit();
}else{
finish();
}
}

You can do it even with out backstack its just my point of view to simplify so that it can help some one.
#Override
public void onBackPressed(){
Fragment f = getSupportFragmentManager().findFragmentById(R.id.container_body);
if(f.getClass().getName().equals(HomeFragment.class.getName())){ // here HomeFragment.class.getName() means from which faragment you actually want to exit
finish();
}else{
displayView(0); //were you want to go when back button is pressed
}
}
private void displayView(int position) {
Fragment fragment = null;
String title = getString(R.string.app_name);
switch (position) {
case 0:
fragment = new HomeFragment();
title = getString(R.string.app_name);
break;
case 1:
fragment = new OffersFragment();
title = getString(R.string.nav_item_offers);
break;
case 2:
fragment = new NotificationFragment();
title = getString(R.string.nav_item_notifications);
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.container_body, fragment);
fragmentTransaction.commit();
// set the toolbar title
getSupportActionBar().setTitle(title);
}
}

Skip some fragments onBackPressed

I am fairly new with android fragments so please bear with me.
I have a bunch of fragments using a single activity as host.
In my mind, my fragments are grouped by sections although they are still modular/reusable by code.
Consider this desired scenario:
Frag1 -> (Press Next) -> Frag2 -> (Press Next) -> Frag3 -> (Press Back) -> Frag1
After going through a series of fragments, I would like to skip some previous fragments (in this scenario, skip Frag 2) on pressing the back button.
However, in my current code, my problem is that even though it goes back to Frag1, Frag3 does not disappear from the screen. What happens is that both Frag1 and Frag3 becomes visible on top of each other.
Here are my relevant code snippets:
Code snippet for creating Frag1
#Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
// init the fragment (with a default fragment, not null)
Fragment fragment = PlaceholderFragment.newInstance(position + 1);
// Position number from navigation sidebar starts from 0.
// Since position starts from 0, add 1 to match section number
// as implemented in {#link #onSectionAttached()}
switch(position) {
case 0:
fragment = PlaceholderFragment.newInstance(position + 1);
break;
case 1: // Frag1 case
fragment = new AddPointsFragment().newInstance(position + 1, "");
break;
default:
break;
}
// update the main content by replacing fragments
FragmentManager fragmentManager = getFragmentManager();
// clear all fragments from previous section from the back stack
fragmentManager.popBackStackImmediate(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
// replace all currently added fragments in container and replace with the new fragment
fragmentManager.beginTransaction()
.replace(R.id.container, fragment)
.commit();
}
Code snippet for creating Frag2
public void onEnterButtonFragmentInteraction(int sectionNumber, String cardNo) {
// TODO: Add point for given card number
int points = 5; //sample points
AddPointsSuccessFragment addPointsSuccessFragment =
new AddPointsSuccessFragment().newInstance(sectionNumber, cardNo, points);
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, addPointsSuccessFragment)
.addToBackStack(null)
.commit();
}
Code snippet for creating Frag3
public void onOkButtonFragmentInteraction(int sectionNumber, String cardNo, int points) {
RedeemRewardFragment redeemRewardFragment =
new RedeemRewardFragment().newInstance(sectionNumber, cardNo, points);
FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.container, redeemRewardFragment);
fragmentTransaction.commit();
}
My current workaround for this is by adding .addToBackStack(null) in creating Frag3 and running this code
public void onBackButtonFragmentInteraction() {
this.onBackPressed(); // simulate pressing of activity back button
FragmentManager fragmentmanager = getFragmentManager();
fragmentmanager.popBackStack(); // pop Frag2 from back stack
}
right after calling the onBackPressed() method. Unfortunately, this workaround is ugly because because there is a split-second appearance of Frag2 before going to Frag1.

So the key to your solution here is this guy:
.addToBackStack(null)
Instead of null, you can pass in a String identifier for that particular transaction -- for instance, the class name of the Fragment is what we use (although that doesn't work if you have multiple instances of the same fragment on the backstack):
.addToBackStack(Fragment1.class.getName())
Then, if you wanted to get back to Fragment1 from Fragment3, just pop using the identifier of the next fragment, and pass the INCLUSIVE flag (which means it will also pop that next fragment that you specified):
getFragmentManager().popBackStack(
Fragment2.class.getName(),
FragmentManager.POP_BACK_STACK_INCLUSIVE);
Which will play your animations as expected, but as if the fragments in between were never there. The reason I suggest to use the next fragment is because you probably don't want your first fragment transaction on the back stack.

You could try this, it should work and doesnt give a split-second delay. Its not beautiful code though, and if somebody has a better way, please post.
1.Give a tag to your fragments.
transaction.add(R.id.main_activity_container, FirstFragment, "FirstFragment");
transaction.replace(R.id.main_activity_container, Second, "SECOND");
transaction.replace(R.id.main_activity_container, Third, "THIRD");
2.Modify your onBackPressed() in your frameActivity (activity) that "houses" your fragments.
#Override
public void onBackPressed() {
// TODO Auto-generated method stub
int lastStack = getSupportFragmentManager().getBackStackEntryCount();
try {
//If the last fragment was named/tagged "three"
if (getSupportFragmentManager().getFragments().get(lastStack).getTag().equalsIgnoreCase("THIRD")){
getSupportFragmentManager().popBackStackImmediate();
getSupportFragmentManager().popBackStackImmediate();
//Get your first fragment that you loaded in the beginning.
Fragment first = getSupportFragmentManager().findFragmentByTag("FirstFragment");
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.main_activity_container, first);
transaction.commit();
return;
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
super.onBackPressed();
}

When you display Frag2 use:
final FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.addToBackStack(FRAG_2);
fragmentTransaction.replace(containerID, frag2, FRAG2_TAG);
and on back press:
#Override
public void onBackPressed() {
final Frag2 frag2 = (Frag2)getSupportFragmentManager().findFragmentByTag(FRAG2_TAG);
if (frag2 != null && frag2.isVisible() && getSupportFragmentManager().getBackStackEntryCount() > 0) {
getSupportFragmentManager().popBackStackImmediate();
return;
}
}
This will prevent from frag2 to be displayed after onBackPressed() called.
Avoid using popBackStack() as this will results in frag2 lifecycle trigger (onCreate, onStart, onResume ...)