Develop Reference

Handling hidden and shown fragments onbackpressed

I have an activity which hosts three Fragment's and I can switch between Fragment's using BottomNavigationView.The mechanism that I use to switch between Fragment's is using show and hide functions of FragmentTransaction instead of replace function of FragmentTransaction. I am doing so because I want some network operations to be done only once and also to inflate Layout only once.
The problem that I am facing using this mechanism is that when I start another Activity from any of the Fragment and then hit the back button the selectedItem of the BottomNavigationView and the Fragment shown are mismatching.
I was able to solve this problem though but I feel it has less efficiency. The procedure was that whenever I clicked a tab in BottomNavigation while switching Fragment's I gave it some predecided number and saved in a static variable(X) and whenever I clicked back button in the OnResume() method of the hosting activity I made a switch-case block using X to know which Fragment was visible before starting the new Activity and then finally making three FragmentTransaction's to show and hide required Fragment's.
protected void onResume() {
super.onResume();
if(selectedId!=63){
switch(selectedId){
case 0:if(bottomNavigationView.getSelectedItemId()==R.id.navigation_home){handleHomeFragmentVisibility();}
break;
case 1:if(bottomNavigationView.getSelectedItemId()==R.id.navigation_dashboard)
{handleDashboardFragmentVisibility();}
break;
case 2:if(bottomNavigationView.getSelectedItemId()==R.id.navigation_notifications)
{handleNotificationFragmentVisibility();}
break;
}
}
I feel using three FragmentTransaction's is costly and I was looking for some efficient way. Can you tell me one if you know ?
public void handleHomeFragmentVisibility(){
FragmentManager fragmentManager= getSupportFragmentManager();
if (fragmentManager.findFragmentByTag("home") != null) {
//if the fragment exists, show it.
fragmentManager.beginTransaction().show(fragmentManager.findFragmentByTag("home")).commit();
} else {
//if the fragment does not exist, add it to fragment manager.
Log.e(TAG,"homeFragmentAdded");
fragmentManager.beginTransaction().add(R.id.container, new HomeFragment(), "home").commit();
}
if (fragmentManager.findFragmentByTag("dashboard") != null) {
//if the other fragment is visible, hide it.
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("dashboard")).commit();
}
if (fragmentManager.findFragmentByTag("requests") != null) {
//if the other fragment is visible, hide it.
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("requests")).commit();
}
}
public void handleDashboardFragmentVisibility(){
FragmentManager fragmentManager= getSupportFragmentManager();
if (fragmentManager.findFragmentByTag("dashboard") != null) {
//if the fragment exists, show it.
fragmentManager.beginTransaction().show(fragmentManager.findFragmentByTag("dashboard")).commit();
} else {
//if the fragment does not exist, add it to fragment manager.
fragmentManager.beginTransaction().add(R.id.container, new DashboardFragment(), "dashboard").commit();
}
if (fragmentManager.findFragmentByTag("home") != null) {
//if the other fragment is visible, hide it.
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("home")).commit();
}
if (fragmentManager.findFragmentByTag("requests") != null) {
//if the other fragment is visible, hide it.
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("requests")).commit();
}
}
public void handleNotificationFragmentVisibility(){
FragmentManager fragmentManager= getSupportFragmentManager();
if (fragmentManager.findFragmentByTag("requests") != null) {
//if the fragment exists, show it.
fragmentManager.beginTransaction().show(fragmentManager.findFragmentByTag("requests")).commit();
} else {
//if the fragment does not exist, add it to fragment manager.
fragmentManager.beginTransaction().add(R.id.container, new NotificationFragment(), "requests").commit();
}
if (fragmentManager.findFragmentByTag("home") != null) {
//if the other fragment is visible, hide it.
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("home")).commit();
}
if (fragmentManager.findFragmentByTag("dashboard") != null) {
//if the other fragment is visible, hide it.
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("dashboard")).commit();
}
}
bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
FragmentManager fragmentManager = getSupportFragmentManager();
switch (item.getItemId()) {
case R.id.navigation_home:
selectedId=0;
handleHomeFragmentVisibility();
break;
case R.id.navigation_dashboard:
selectedId=1;
handleDashboardFragmentVisibility();
break;
case R.id.navigation_notifications:
selectedId=2;
handleNotificationFragmentVisibility();
break;
}
return true;
}
});

A first note on your code: Avoid boilerplate! Write only one method instead of three and use a signature of the type handleFragmentVisibility(String show, String hide1, String hide2, int container). In case the fragment to be shown is null, instantiate it by testing for show, something like:
Fragment newFragment = (show == "home") ? new HomeFragment() : (show == "dashboard") ? new DashboardFragment() : new NotificationFragment();
However, none of your fragments should ever get null through hiding (please check for yourself), since you don't remove them from your activity or replace them with other fragments. Instead of using show and hide you could also use attach and detach, both sets of methods keep state. I don't see an efficiency problem and you do indeed need to call three FragmentTransactions. It only can be done with less code:
public void handleFragmentVisibility(String show, String hide1, String hide2){
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().show(fragmentManager.findFragmentByTag(show)).commit();
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag(hide1)).commit();
fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag(hide2)).commit();
}
Please note, that although this method keeps the state of the fragment while hiding or detaching them, other events like orientation change still make it necessary that you take care of saving state in onSaveInstanceState(Bundle savedInstanceState).

fragments sometimes overlap - Android

I have a navigation drawer and clicking on items shows/hides/creates full screen fragments.
For the most part, this code works great. But sometimes, maybe 1% of the time, I will get crazy full screen fragment overlapping when opening the app while it has already been running.
Is the problem with my code..? Or maybe something else in Android where it does not recognize I have the fragments with the tags already created?
Here is the relevant code for how I show/hide/create fragments:
#SuppressWarnings("StatementWithEmptyBody")
#Override
public boolean onNavigationItemSelected(MenuItem item) {
// Get to drawer layout so we can interact with it
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
// Get the fragment manager to remove/add fragments
FragmentManager fragmentManager = getSupportFragmentManager();
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_profile) {
// Hide visible fragment
fragmentManager.beginTransaction().hide(getVisibleFragment()).commit();
// Check if the fragment exists first.
if(fragmentManager.findFragmentByTag("profileFragment") != null) {
// If the fragment exists, show it (no reason to recreate it).
fragmentManager.beginTransaction()
.show(fragmentManager.findFragmentByTag("profileFragment"))
.commit();
} else {
// If the fragment does not exist, add it to fragment manager with a tag to identify it.
// Create new fragment instance with required argument(s).
ProfileFragment fragment = ProfileFragment.newInstance();
fragmentManager.beginTransaction()
.add(R.id.content_frame, fragment, "profileFragment")
.commit();
}
// Set the title
mToolbarTitleTextView.setText(R.string.title_activity_profile);
} else if (id == R.id.nav_feed) {
// Hide visible fragment
fragmentManager.beginTransaction().hide(getVisibleFragment()).commit();
// Check if the fragment exists first.
if(fragmentManager.findFragmentByTag("feedFragment") != null) {
// If the fragment exists, show it (no reason to recreate it).
fragmentManager.beginTransaction()
.show(fragmentManager.findFragmentByTag("feedFragment"))
.commit();
} else {
// If the fragment does not exist, add it to fragment manager with a tag to identify it.
fragmentManager.beginTransaction()
.add(R.id.content_frame, new feedFragment(), "feedFragment")
.commit();
}
// Set the title
mToolbarTitleTextView.setText(R.string.title_activity_feed);
} else if (id == R.id.nav_notifications) {
// Hide visible fragment
fragmentManager.beginTransaction().hide(getVisibleFragment()).commit();
// Hide the post button
mPostButton.setVisibility(View.GONE);
// Check if the fragment exists first.
if(fragmentManager.findFragmentByTag("notificationsFragment") != null) {
// If the fragment exists, show it (no reason to recreate it).
fragmentManager.beginTransaction()
.show(fragmentManager.findFragmentByTag("notificationsFragment"))
.commit();
} else {
// If the fragment does not exist, add it to fragment manager with a tag to identify it.
fragmentManager.beginTransaction()
.add(R.id.content_frame, new NotificationsFragment(), "notificationsFragment")
.commit();
}
// Set the title
mToolbarTitleTextView.setText(R.string.title_activity_notifications);
}
mDrawerLayout.closeDrawer(GravityCompat.START);
return true;
}
// Useful method to hide the currently visible fragment
public Fragment getVisibleFragment(){
FragmentManager fragmentManager = MainActivity.this.getSupportFragmentManager();
List<Fragment> fragments = fragmentManager.getFragments();
if(fragments != null){
for(Fragment fragment : fragments){
if(fragment != null && fragment.isVisible())
return fragment;
}
}
return null;
}
EDIT: It is really hard to reproduce this error which makes it hard to debug. It seems to randomly happen.

Why hide and keep all the fragments with fragmentManager.beginTransaction().add(); you can avoid this error by keeping only one fragment in memory and avoiding the hassle of hiding fragments by using fragmentManager.beginTransaction().replace() and using the fragment lifecycle methods to store the fragment state if necessary.

Here is how I solved the problem. In my MainActivity I did this:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(null);
setContentView(R.layout.activity_main);
}
Basically what was happening is if I had 1+ fragments on the screen, if the android system ran low on resources while the app was in the background and shut it down, when restored, MainActivity.onCreate() would be called and it would re-instantiate all the fragments with the call
super.onCreate(savedInstanceState);
So I just made it null and this prevents from all those fragments to be recreated.
The reason they are overlapping is because they were all getting shown at once.
Definitely not the correct way to do it, but it solves my problem right now =P

Android Navigation Drawer Fragment Not Showing

I have implemented a navigation drawer in my application, The application is a tabbed layout and I think this is where the problem is coming from.
AT the moment I have a listener on the items in the Nav drawer to launch a new fragment when pressed. The issue is that when I press one of the items the fragment doesnt seem to load and the current fragment just goes blank.
How do I set the layout of the fragment to launch once the item has been selected? As my current method doesnt seem to be working. The below shows my current attemp where R.id.viewpager is what I am trying to replace. Is there a way of just launching the fragments layout and completely replacing the layout with the new fragments layout?
onDrawerItemSelected
#Override
public void onDrawerItemSelected(View view, int position) {
Fragment fragment = null;
String title = getString(R.string.app_name);
switch (position)
{
case 0:
{
Intent intent = new Intent(MainActivity.this, MainActivity.class);
startActivity(intent);
}
case 1:
fragment = new FavouritesFragment();
title = getString(R.string.title_favourites);
break;
case 2:
fragment = new HelpFragment();
title = getString(R.string.title_help);
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.viewpager, fragment);
fragmentTransaction.commit();
// set the toolbar title
getSupportActionBar().setTitle(title);
}
}

fragmentTransaction.replace(R.id.viewpager, fragment);
You don't replace the viewpager, you set current item for the viewPager. You should have a PagerAdapter that defines which fragment to show for the position.

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);
}
}

Android Navigation Drawer Fragment State

I'm currently utilizing the Navigation Drawer for my Android APP. In my first fragment, I've a fragment that loads data using Facebook's Graph API. Thus, when my App is first loaded, it first goes to the first fragment.
Then, I use the Navigation Drawer to click on another Fragment and view it.
And then finally, I reuse the Navigation Drawer to proceed back to the first Fragment and view it.
My issue that I'm facing is, how do I proceed to utilize the Fragment that has been created once instead of re-creating it whenever the Navigation Drawer Item is selected. My code for the switching of the fragments are as shown below.
private void displayView(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
switch (position) {
case 0:
fragment = new SelectionFragment();
break;
case 1:
fragment = new HomeFragment();
break;
case 2:
fragment = new PhotosFragment();
break;
case 3:
fragment = new CommunityFragment();
break;
case 4:
fragment = new PagesFragment();
break;
case 5:
fragment = new SplashFragment();
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.frame_container, 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 noticed that there is indeed a "new" instance of the Fragment every time whenever the option is selected. How do I go about implementing the logic of creating the Fragment instance ONCE and reusing it, so that I do not have to continuously load the Fragment over and over again.

To anyone who encounters the same issue with me,I've managed to find a solution.
In the container frame,I've to define specific fragment views that I'll be utilizing as shown below.
In each Fragment view,I've to "link" it with the actual Fragment itself as shown below via the "android:name" attribute.Do take note of the the path to the Fragment,example for in my case it's com.example.confesssionsrp.SelectionFragment.
<fragment
android:id="#+id/selectionFragment"
android:name="com.example.confessionsrp.SelectionFragment"
android:layout_width="match_parent"
android:layout_height="match_parent" />
In the the MainActivity(or the Activity where we're viewing the fragments),create variables for each of the Fragments as shown below.
Following that,in the Oncreate of the MainActivity(or your specific Activity),initialize the various fragments as shown below.
Proceed onto creating a new Method called "ShowFragment" as shown below.
private void showFragment(int fragmentIndex, boolean addToBackStack) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction transaction = fm.beginTransaction();
for (int i = 0; i < fragments.length; i++) {
if (i == fragmentIndex) {
transaction.show(fragments[i]);
if (Session.getActiveSession().isClosed()) {
mDrawerLayout
.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED);
}
} else {
transaction.hide(fragments[i]);
}
}
if (addToBackStack) {
transaction.addToBackStack(null);
}
transaction.commit();
}
From then on in the switching of the fragments,manually call upon the "ShowFragment" method with the selected Fragment as shown below.
Doing all of this overall,will not reset the Fragment each time we view it,and therefore is the solution to the answer.Thank you for anyone who has helped me so far :)!

I am using the following code:
#Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
FragmentManager fragmentManager = getFragmentManager();
if(position==0){// selection of tabs content
fragmentManager
.beginTransaction()
.replace(R.id.container,
SimulatorFragment.newInstance(position + 1)).commit();
}else if(position==1){
fragmentManager
.beginTransaction()
.replace(R.id.container,
HudFragment.newInstance(position + 1)).commit();
}else if(position==2){
// Display the fragment as the main content.
fragmentManager
.beginTransaction()
.replace(R.id.container,
SettingsBasicFragment.newInstance(position +1)).commit();
}else{
}
}
You can replace by a new instance the first time and store the fragment, if it is not null, then replace by the stored fragment.
The activity must implement NavigationDrawerFragment.NavigationDrawerCallbacks
The fragment constructor and newInstance methods look like this:
public final class HudFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section number.
* #param simulation
*/
public static HudFragment newInstance(int sectionNumber) {
HudFragment fragment = new HudFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public HudFragment() {
}
To switch fragments by code I use this method inside the NavigationDrawerFragment:
/**
* Select a different section
* #param position
*/
public void select(int position){
selectItem(position);
}
private void selectItem(int position) {
mCurrentSelectedPosition = position;
if (mDrawerListView != null) {
mDrawerListView.setItemChecked(position, true);
}
if (mDrawerLayout != null) {
mDrawerLayout.closeDrawer(mFragmentContainerView);
}
if (mCallbacks != null) {
mCallbacks.onNavigationDrawerItemSelected(position);
}
}

The second option is to start with the example of navigationDrawer that Android SDK offers. I selected that template of activity when creating the project and almost all the code of my previous answer is produced automatically.
If you want to keep the fragments after device rotation or similars it is a different thing, you need then to retain the fragments. If not, you just need to save the new instance of the fragment in a variable and check if it is null to create a new one or use the old one.

In case someone want's a different approach to this: you could find the fragment on the stack:
// check if this fragment is on the backstack to avoid creating a new one
Fragment foundFragment = fragmentManager.findFragmentByTag("unique_fragment_tag");
if (foundFragment != null) {
fragmentManager.popBackStackImmediate("unique_fragment_tag", 0);
return;
}