Develop Reference

Fragment not attached to host

Let me explain the whole thing, just in case. I'm using BottomNavigationView with Jetpack's Mobile Navigation graphs and so. I reimplemented the method:
NavigationUI.setupWithNavController(...)
during navigation setup, instead of using this method I made a very similar:
customSetupWithNavController(...)
the only changes I made was to change de default fading transition between fragments, and started to using more natural (in my opinion) side slide animations, just like this in onNavDestinationSelected:
if(origin == 0){
builder.setEnterAnim(R.anim.slide_in_from_right)
.setExitAnim(R.anim.slide_out_to_left)
.setPopEnterAnim(R.anim.slide_in_from_left)
.setPopExitAnim(R.anim.slide_out_to_right);
}else if(origin == 1){
builder.setEnterAnim(R.anim.slide_in_from_left)
.setExitAnim(R.anim.slide_out_to_right)
.setPopEnterAnim(R.anim.slide_in_from_right)
.setPopExitAnim(R.anim.slide_out_to_left);
}
Where origin stands for the direction where the incoming Fragment comes from.
It came with a problem: 2 of my fragments need a FAB to add elements to a recycler, and the side slide transitioning suddenly became ugly. So I added a single FAB in MainActivity's Layout, and a logic shows the FAB only when these 2 fragments are called.
I couldn't find a nice way to pass the click event from Activity to Fragments, because I wasn't able to instantiate the Fragments, since the Navigation handles the whole process.
So, what I did was to create a ViewHolder, since I know it can survive trough lifecycle changes. This ViewHolder holds an int, and a MutableLiveData, in the MainActivity logic I pass the current selected id of the element selected by the BottomNavigationView to the int, and only if the MainActivity's FAB is clicked the live Boolean is set to true. So, in Fragments onViewCreated() I added and observer to this Boolean, when the value is set to true, and the id passed to the ViewHolder matches with the id of the current fragment, the Boolean is set back to false, and something can be done, it's something like this:
eventsNotificationHandler.getClickEvent().observe(requireActivity(), new Observer<Boolean>() {
#Override
public void onChanged(Boolean aBoolean) {
if(aBoolean && eventsNotificationHandler.getPositionId() == R.id.nav_contacts){
eventsNotificationHandler.setClickEvent(false);
//do something here
}
}
});
This notificationHandler is the ViewHolder.
So far so good, at this point I can:
1- Navigate between BottomNavigationView' Fragments freely, and the FAB shows only for needed fragments.
2- Use Log.d(...) inside the observer any time I want, and see that the debug message just fine.
3- Toast a message, any time I want, ONLY if the context parameter was initialized outside the Observer, something like this:
Toast.makeText(previouslyDefinedContext, "SOME TEXT", Toast.LENGTH_SHORT).show();
What I can't:
1- Launch an Activity whenever I want, from inside the observer by using same idea than before, ONLY initializing the context before, and outside the Observer I was able to start the intent, just like this:
eventsNotificationHandler.getClickEvent().observe(requireActivity(), new Observer<Boolean>() {
#Override
public void onChanged(Boolean aBoolean) {
if(aBoolean && eventsNotificationHandler.getPositionId() == R.id.nav_contacts){
eventsNotificationHandler.setClickEvent(false);
Intent newContact = new Intent(previouslyDefinedContext, NewContactActivity.class);
startActivity(newContact);
requireActivity().overridePendingTransition(R.anim.slide_in_from_right,R.anim.slide_out_to_left);
}
}
});
But in this particular case I can launch the new Activity as many times as I want, BUT ONLY if I navigate directly to this particular fragment where the observer is defined after the app opens, if I decide to navigate first trough some other fragments instead, and then I go to this fragment to try to launch the Activity, the app crashes
I've noticed that this exact behavior happens when I call requireContext() from inside the Observer, it works but then stops working.
The app crashes with:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: cu.arrowtech.bpawreckproject, PID: 18019
java.lang.IllegalStateException: Fragment FragmentContacts{883259b} (9f127bdb-127d-4366-b90b-c8900a5a771e)} not attached to Activity
What I want:
1- A right way to launch a new Activity from inside a Fragment, by pressing a FAB in MainActivity, if it's possible.
2- A nice way to switch fragments if a possible solution implies to change the logic I have already.
3- Keep using Jetpack and Navigation Graphs.
I'm able to do what I want by using 2 separate FABs in each Fragment, but the transitioning is not nice and beautiful.
I'm open to suggestions, even if that implies to change the logic. I'm almost certain it must be a better way to do what I'm doing, instead of using ViewHolder for this purpose.
I would like to get something similar to the Google Pay, it seems to be that the Buttons for adding payment method, passes, and transfers is the same button, but it adapts to each situation.

After some reasearch I did found a way to keep fluid transitions between fragments AND Mobile Navigation components AND a single FAB in the MainActivity layout.
What I did was to use an Interface instead of ViewModels (I always knew that approach was wrong):
public interface SharedViewsInterface {
void onFabClicked();
}
So in my MainActivity I defined that interface as null, and created a method to define it according to the situation. My MainActivity looks like:
public class MainActivity extends AppCompatActivity {
//UI elements
private FloatingActionButton main_fab;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//Same dode to get the custom animations
//.......
//Main and only Fab configuration
main_fab = findViewById(R.id.main_fab);
main_fab.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(sharedViewsInterface !=null){
sharedViewsInterface.onFabClicked();
}
}
});
}
//Other auxiliary methods
public void setInterface(SharedViewsInterface sharedViewsInterface){
this.sharedViewsInterface = sharedViewsInterface;
}
}
By doing this, I can, from each fragment to implement the Interface in onCreate by doing this:
((MainActivity) requireActivity()).setInterface(new SharedViewsInterface() {
#Override
public void onFabClicked() {
Intent newContact = new Intent(requireContext(), NewContactActivity.class);
startActivity(newContact);
requireActivity().overridePendingTransition(R.anim.slide_in_from_right_short,R.anim.slide_out_to_left_medium);
}
});
This works well becouse the FAB is shown only when a fragment with Interface implementation is visible, see my example gif

Save BottomNavigationView selected item during screen rotation

Using ASL's 25.0 BottomNavigationView i'm faced with some troubles, like a save selected item (or his index) and selected item programmatically.

Unfortunately, there are plenty of features missing in BottomNavigationView at this stage.
Your question was really interesting and I wrote this extended BottomNavigationView that preserves the state and, in your case, saves last selected item.
Here is gist to the code
This extension includes:
Gives public two method to set and get selected items programatically.
Saves and restores state only for the last selection.
Lets wait until ASL devs fix this.

Agree with Nikola!
I created my own gist too
To save state after rotation you need add to you Activity:
#Override
protected void onSaveInstanceState(Bundle outState) {
outState.putInt("opened_fragment", bottomNavigation.getCurrentItem());
super.onSaveInstanceState(outState);
}
and into onCreate method, just after setting up BottomNavigationView:
final defaultPosition = 0;
final int bottomNavigationPosition = savedInstanceState == null ? defaultPosition :
savedInstanceState.getInt("opened_fragment", defaultPosition);
bottomNavigation.setCurrentItem(bottomNavigationPosition);
The biggest plus of this gist is: There are few kinds of listeners, it shows you previous selection position and listeners react even when the position is set programmatically. Everything is written in link, use if you need.

I am working with BottomNavigationView and here is the code with which the app is working correctly on screen rotation.
Firstly, I created a variable to hold the id of selected menu
private int saveState;
Saving the value of id by taking the selected menu id in the variable
#Override
protected void onResume() {
super.onResume();
navigation.setSelectedItemId(saveState);
}
#Override
public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
super.onSaveInstanceState(outState, outPersistentState);
saveState = navigation.getSelectedItemId();
}
Then in the onCreate method retrieving the value of id if available
if(savedInstanceState!=null){
navigation.setSelectedItemId(saveState);
}else{
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.content, MapFragment.newInstance());
transaction.commit();
}

I was having the same problem and what I did was to update from 25.0.1 to 25.3.1 and it started working correctly without the need of no additional code. You can check the Support Library Revision website for the latest version.
I hope it helps.

Save App Preferences from PreferenceScreen when pressing back button

I'm trying to learn how to develop Android apps. I followed a video tutorial on YouTube, and it ended by adding a simple App Settings screen to the application.
However, there's one point that bothers me: when I press the back button on my phone's navigation bar, the changed settings aren't applied.
I have tried searching on Google, but none of the solutions I found have worked. The fact that I don't yet understand 100% of what's happening on the proposed solutions may also contribute to my difficulty on solving this one problem.
The behavior I expect from the app is that when I press the back button on the navigation bar, the changed settings should be applied.
For instance, I have a setting for dark background, which is controlled by a checkbox. The current behavior is: I check the setting for dark background. When I press the back button on the navigation bar, the setting isn't applied (I do have a method that loads the preferences on my MainActivity). What I want to happen is when I press the back button, the dark background is applied in this case.
From what I understand, I believe that overriding onBackPressed should do the trick, but I don't know what should be executed in order to properly apply the settings.
Here are the class and layout of my PreferenceScreen. Regarding the strings on the XML, they aren't actually hard-coded. I just copied the English values here to show the text that should appear on the interface.
public class AppPreferences extends AppCompatActivity
{
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_note_detail);
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
SettingsFragment settingsFragment = new SettingsFragment();
fragmentTransaction.add(android.R.id.content, settingsFragment, "SETTINGS_FRAGMENT");
fragmentTransaction.commit();
}
public static class SettingsFragment extends PreferenceFragment
{
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.app_preferences);
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
<PreferenceCategory
android:title="General">
<EditTextPreference
android:title="Notebook"
android:summary="The title that will be used on the main action bar."
android:key="title"
android:defaultValue="Notebook" />
</PreferenceCategory>
<PreferenceCategory
android:title="Color">
<CheckBoxPreference
android:title="Dark Background"
android:summary="Is the main background color dark?"
android:key="background_color"
android:defaultValue="false" />
</PreferenceCategory>
</PreferenceScreen>

You will need to use
public class AppPreferences extends AppCompatActivity
{
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
//setContentView(R.layout.activity_note_detail);
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
SettingsFragment settingsFragment = new SettingsFragment();
fragmentTransaction.add(android.R.id.content, settingsFragment, "SETTINGS_FRAGMENT");
fragmentTransaction.commit();
}
public static class SettingsFragment extends PreferenceFragment
{
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.app_preferences);
Preference preference = findPreference("background_color");
preference.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
#Override
public boolean onPreferenceChange(Preference preference, Object newValue) {
//do your action here
return false;
}
});
}
}
}
Or from other activity:
PreferenceManager.setDefaultValues(this, R.xml.your_setting_xml, false);
SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(this);
if (settings.getBoolean("background_color", true)) {
//do your action here
.........
Refer to this question also, (it has similar use case):
Checkbox Preference and Checking if its enabled or disable

Like #Chisko said, there isn't enough code in your question for us to be able to figure out your end goal - although I'm guessing you are wanting some form of persistent storage for your app to be able to save your app preferences. For this, you will want to use something in Android called SharedPreferences. This allows you to save simple data types to be accessed later.
Give that link a read, and then try saving/loading one simple piece of data. You'll want to load it from SharedPreferences on starting the activity (you can specify a default value if it hasn't been saved yet) and then you'll want to save the data in onBackPressed() as you said.
Best of luck and if you run into any issues, just comment here.

#Abdulhamid Dhaiban correctly points it out.
I'll add to your suggestion about overriding the onBackPressed() method.
If your "Up" button (top left <-) provides the correct result, then you can set the Back button to behave like the Up button by just adding the following code:
#Override
public void onBackPressed() {
super.onBackPressed();
NavUtils.navigateUpFromSameTask(this);
}
Hope it helps!

Callback when Fragment is replaced and when it is visible again

I've been researching this topic but so far no luck. Basically I'm replacing a fragment (A) with another one (B) using FragmentTransaction.replace. In this other fragment (B) I have a 'Cancel' button in the toolbar which when pressed pops back to the previous transaction (A) by calling getActivity().getSupportFragmentManager().popBackStackImmediate().
The problem is I need to update the Activity toolbar to display a different title when I'm showing fragment A and fragment B. I can't seem to find a method which gets called in fragment A whenever I go from A -> B -> A to inform me that it is visible again. The idea is to set the toolbar title in this callback which I cannot seem to find.
Can anyone point me in the right direction please?
Cheers.
Edit:
Method I call to replace the fragment with another one is as follows:
public static void replaceFragment(FragmentActivity parentActivity, int fragmentToReplaceId, Fragment withFragment, Integer enterAnim, Integer exitAnim)
{
FragmentManager fragmentManager;
FragmentTransaction transaction;
fragmentManager = parentActivity.getSupportFragmentManager();
transaction = fragmentManager.beginTransaction();
if ( (null != enterAnim) &&
(null != exitAnim) )
{
transaction.setCustomAnimations(enterAnim, exitAnim);
}
transaction.replace(fragmentToReplaceId, withFragment);
transaction.addToBackStack(null);
transaction.commit();
}

You can inform by overriding method onResume() in fragment and sending the message to activity or changing the Toolbar directly.
#Override
public void onResume() {
super.onResume();
((AppCompatActivity) getActivity()).getSupportActionBar().setTitle("Title");
}

In one activity, when replace A ---> B (A and B both are fragments), can use this call-back:
#Override
public void onAttachFragment(Fragment fragment) {
}

Solved by creating a simple static method in fragment A as follows:
public static void updateActivityTitle(FragmentActivity activity)
{
activity.setTitle(kActivityTitle);
}
Then I'm calling this method in fragment B as follows:
// cancel button has been pressed
private void cancel()
{
INV_CustomersFragment.updateActivityTitle(getActivity());
getActivity().getSupportFragmentManager().popBackStackImmediate();
}
Not ideal but it gets the job done. Any other solution involving a proper callback would be better
Update:
A better solution is the one described by #Rani at Fragment's onResume() not called when popped from backstack. This is more elegant and more maintainable, in fact I implemented this solution in my project. Compared to an equivalent solution for iOS this is still messy if you ask me, still seems the way to go.

DialogFragment dismiss() does not pop backstack

I have a simple DialogFragment that calls dismiss when exits, according to the documentation:
public void dismiss()
Dismiss the fragment and its dialog. If the fragment was added to the
back stack, all back stack state up to and including this entry will
be popped. Otherwise, a new transaction will be committed to remove
the fragment.
however, I found that the fragment is still on the backstack after calling dismiss() so I have to click back button to clear it. Does anyone know why ?
here's my code:
public void onCreate(Bundle b) {
super.onCreate(b);
setContentView(R.layout.test_layout);
class MyDialogFragment extends DialogFragment implements OnClickListener{
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.hello_world, container, false);
Button b = (Button)v.findViewById(R.id.btn);
b.setOnClickListener(this);
return v;
}
#Override
public void onClick(View v) {
dismiss();
}
}
getFragmentManager().beginTransaction().add(android.R.id.content, new MyDialogFragment(), "test").addToBackStack("b").commit();
}
#Override
public void onBackPressed() {
if (getFragmentManager().getBackStackEntryCount() > 0 ){
getFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
}
}
I also found out that if I don't override onBackPressed(), the back button simple doesn't work, no matter how many fragments I add to the activity, the back button always exits the activity right away.

I can confirm what #Luksprog said in his comment: the dialog must be started through show(FragmentTransaction, String).
Note after looking the source: make sure to call addToBackStack(String) on the supplied transaction or else it still won't work.

That it's a wrong way to create a DialogFragment.
Never ever use the FragmentManager to show a DialogFragment. To be shown there are a method called show(FragmentTransacion, String).
In java:
MyDialogFragment mDialogFragment = new MyDialogFragment();
mDialogFragment.show(getFragmentManager(), "MyDialogFragment");
For another hand, to dismiss the dialog just do this:
mDialogFragment.dismiss()
Another think that I would like to highlight is that the MyDialogFragment class is defined inner onCreate method :'(
Please, define the class outside the method or in another file if you want :)
Good Look!

dismiss()
findNavController().navigate(FirstBottomSheetDialogDirections.actionFirstSheetToSecondSheet())
This code is always the wrong thing to do: dismiss() is an asynchronous operation that doesn't actually dismiss anything immediately. That is unlike the navigate() which does immediately update the NavController's state, stacking the new dialog destination on top of the previous one.
This means that when the asynchronous dismiss actually happens, it correctly removes the dialog and, because it is a navigation stack, removes everything on top of it - including your second dialog. However, due to a bug in the DialogFragmentNavigator, we don't actually dismiss that second dialog, which is why it appears to work, despite everything actually already being internally out of sync (thus causing the later crash).
The correct way to pop a destination and navigate to a new destination as an atomic, immediate operation is to use popUpTo and popUpToInclusive. Therefore you can fix the sample app by removing the call to dismiss() and updating the action to pop the first dialog as part of the navigate call:
<action
android:id="#+id/action_firstSheet_to_secondSheet"
app:destination="#id/secondSheet"
app:popUpTo="#id/firstSheet"
app:popUpToInclusive="true"/>
This correctly pops the first dialog off the back stack and then navigates to the new dialog destination.
please refer this link : https://issuetracker.google.com/issues/191073055