I have a support library fragment that sends a network call, and recreate() the parent activity when it receives a specific network response. I can see that the activity does get recreated as I can see the onCreate() and onDestroy() are called.
But after the activity is recreated, the fragment is still there and it got stuck in a loop which keep recreating and making new fragments.
Here's part of the onCreate() of the activity:
if (someLogic()) {
fragmentA = new FragmentA();
FragmentUtil.addFragment(getSupportFragmentManager(), fragmentA);
} else {
fragmentB = new FragmentB();
FragmentUtil.addFragment(getSupportFragmentManager(), fragmentB);
}
FragmentA is the one that does the network call, and FragmentB is the fragment that should be displayed after the recreate(). When I check the list of fragments with getSupportFragmentManager().getFragments() I see 1 instances of FragmentA, and 16 instances of FragmentB.
My question is why does this happen, and how do I fix it?
Calling recreate() essentially causes the Activity to go through a configuration change. A configuration change causes both the Activity and its Fragments to be destroyed and recreated. So your Fragments should in fact be destroyed when this occurs (you can see for yourself by adding a Log message in your fragment's onDestroy method).
The fact that configuration changes cause fragments to be destroyed and created however does not mean that the FragmentManager will simply forget the fragments ever existed. The FragmentManager will still hold a reference to the newly created fragment after the configuration change occurs.
One thing you can do to prevent multiple fragments from being created is by doing something like this in your activity's onCreate():
if (savedInstanceState == null) {
// The Activity is being created for the first time, so create and
// add new fragments.
} else {
// Otherwise, the activity is coming back after being destroyed.
// The FragmentManager will restore the old Fragments so we don't
// need to create any new ones here.
}
I had same situation as #spy wrote, recreating the Activity after Day/Night mode is changed. Activity had four Fragments which they get restored after Activity.recreate() is called, because FragmentManager saves them as #Alex Lockwood stated. But restoring and not adding Fragments after recreation does not help me because of some architectural reasons of project, i wanted them to disappear.
Solution is to delete Fragments from FragmentManager just before Activity.recreate()is called, in my case it is in Activity.onStart():
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
Fragment fragmentA = fragmentManager.findFragmentByTag("fragmentATag");
if(fragmentA != null)
fragmentTransaction.remove(fragment);
// Find and delete other Fragments
fragmentTransaction.commit(); // or commitAllowingStateLoss()
recreate();
This way you will not get Fragments restored when Activity.onCreate() is called.
Related
I have a thread which triggers a callback method in my Activity which has a fragment. The Activity then calls a method within the Fragment to refresh the UI with new info. In that method, getString() is called. When getstring() is called, I get a 'Fragment not Attached to Activity error'. This UI refreshing error is guarded runOnUIThread. The fragment is added like so:
FragmentManager fm = getSupportFragmentManager();
fm.beginTransaction()
.add(fragmentContainerID, fragment, tag)
.commit();
fm.executePendingTransactions();
The activity uses two different layout files for horizontal and vertical orientation. Their are two fragment containers in both layouts. They have the same names in both horizontal and vertical layouts, but they do not match each other. The fragments are added using the above code the first time the Activity is created. On orientation changes, the fragments are automatically added into the layouts because the fragment containers have the same ids in both vertical and horizontal orientation.
When the savedInstanceState is not null, I get a reference to the fragments by using
fm.findFragmentByTag
Can anyone please tell me what I am doing wrong ? The fragments are visibly added to the Activity perfectly fine, and several minutes go by before this thread callback occurs, so I don't see how the Fragment is not "attached".
EDIT: Sigh, after some debugging Ive found that adding fragments in this way is perfectly fine. Code elsewhere in the Activity ( I registered for a callback twice) caused my fragment not attached error. If anyone reading this is getting this error, keep in mind that this issue can be triggered from elsewhere. Also, you have to setRetainInstance to true in the fragment to avoid it being recreated. Tags alone don't do that.
Fragments are added one-per-container so if you are using .add(fragmentContainerID, fragment, tag) ensure firstly that fragmentContainerID is different for each of the fragments added.
However, these sorts of issue are most often caused by a misunderstanding in how orientation changes are handled. When you change orientation and let the oncreate handle the adding: you get a new fragment of the same type what this means is that if your background task has a reference to your fragment - it has a reference to the old (now detached) fragment. What you need to do is to make sure the same fragment gets added to the tag (not a new instance). To do that just don't (re)create a fragment instance when we are only restoring state
public class MyActivity ... {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FragmentManager fm = getSupportFragmentManager();
if (savedInstanceState == null) {
MyFragment frag = new MyFragment();
frag.setArguments( getIntent().getExtras() ); //if it takes params
fm.beginTransaction().add(fragmentContainerID, frag, tag).commit();
}
//after this point a call to MyFragment frag = (MyFragment) fm.findFragmentByTag(tag); should always return the correct fragment
}
It's probably also a wise idea for your task to look for the fragment right when it does its callback to update the UI (and NOT to hold on to a reference to it). Depending on how you've set up your task it just means changing from FragmentManager fm = getSupportFragmentManager(); then the task is created, to calling it as part of the onPostExecute
When change orientation, fragment automatically added to FragmentManager and forget own tag!!
Use this code to find your fragment:
FragmentManager fragmentManager= getSupportFragmentManager();
for (Fragment fragment : fragmentManager.getFragments())
{
if(fragment instanceof MyFragment)
myFragment = (MyFragment)fragment;
}
After you find the fragments on orientation change, try detaching them and then reattaching them before any operation. Or if that does not work remove them and add them. then continue..... I have even had to sometimes put a time delay of a few millisec after detach and before attach to ensure all OK.
I'm having an issue of having two instances of the same fragment being attached to the activity. I have ActivityA attaching FragmentA on onCreate. When I leave the app while being on this Activity, browse other apps for a while, and return to the app, I see that the system is trying to re-create the activity. My log shows the code from the Fragment being ran TWICE. My guess is the Fragment is already attached but then the Activity attempts to create a new instance of FragmentA.
What happens to the Activity/Fragment when the system removes them from memory, and what's the best way to handle this? Any links would be helpful.
Will provide code if needed.
The best way to handle this is to check in your onCreate() method if your activity if being recreated from a previous state or not. I'm assuming you add your fragment on the onCreate() method of your activity. You can do something like this:
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
if (savedInstanceState == null)
{
// Add the fragment here to your activity
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.content, new YourFragment());
ft.commit();
}
}
By doing this, you are basically saying that if a previous state is not found, you add your fragment. Otherwise you automatically get back the fragment that already exists.
I am rewriting a Bluetooth app with 3 Activities to use just 1 Activity and 3 Fragments:
So I have now 4 files:
MainActivity.java (contains bluetooth and shared preferences code)
MainFragment.java (contains ellipsis menu to show SettingsFragment)
SettingsFragment.java (contains "scan" button to show ScanningFragment)
ScanningFragment.java (displays nearby bluetooth devices in a list)
It almost works, but as an Android programming newbie I don't understand - what to do with Fragments when I show some other Fragment?
Should I just drop the Fragments (and remove from FragmentManager?) to be garbage collected?
Or should I add these 3 private variables to MainActivity.java and reuse them (when the user navigates forwards and backwards)?
private MainFragment mMainFragment;
private SettingsFragment mSettingsFragment;
private ScanningFragment mScanningFragment;
Or does FragmentManager somehow manage all 3 Fragment for me - regardless if they are visible or not?
Here is my current code (it is simple, I just call replace() all the time)-
public class MainActivity extends Activity implements
MainListener,
SettingsListener,
ScanningListener,
BleWrapperUiCallbacks {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
setContentView(R.layout.activity_main); // empty FrameLayout
Fragment fragment = new MainFragment();
getFragmentManager().beginTransaction()
.replace(R.id.root, fragment, "main")
.commit();
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_settings:
Fragment fragment = new SettingsFragment();
getFragmentManager().beginTransaction()
.addToBackStack(null)
.replace(R.id.root, fragment, "settings")
.commit();
break;
}
return super.onOptionsItemSelected(item);
}
// implementing SettingsFragment.SettingsListener interface
public void scanClicked() {
// TODO how to stop indicator when returned?
setProgressBarIndeterminateVisibility(true);
String address = // get from shared preferences
Fragment fragment = ScanningFragment.newInstance(address);
getFragmentManager().beginTransaction()
.addToBackStack(null)
.replace(R.id.root, fragment, "scan")
.commit();
}
Should I just drop the Fragments (and remove from FragmentManager?) to
be garbage collected?
No need to do anything else. FragmentManager is the guy in charge of Fragments' lifecycle. Once you call replace(), FragmentManager takes care for the rest. If needed it will keep fragment in memory, or release it.
Or should I add these 3 private variables to MainActivity.java and
reuse them (when the user navigates forwards and backwards)?
No, don't do it because of the said above.
Or does FragmentManager somehow manage all 3 Fragment for me -
regardless if they are visible or not?
Yes, it does. For instance, if you have invisible retained fragment, it's enough to create it once, and FragmentManager will take care of it and will keep it even when activity gets re-created during configuration change.
If you create fragments dynamically (as far as I can see, this is your case) then I suggest to add very first fragment dynamically too. You can do it like this.
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
setContentView(R.layout.activity_main); // empty FrameLayout
if (savedInstanceState == null) { // <- important
Fragment fragment = new MainFragment();
getFragmentManager().beginTransaction()
.replace(R.id.root, fragment, "main")
.commit();
}
}
This will ensure you don't duplicate MainFragment on configuration change, because when savedInstanceState is not null, then FragmentManager keeps instance of your fragment already.
Since you are calling .replace() on the fragment manager it's essentially the same thing as calling .remove(). According to the docs:
This is essentially the same as calling remove(Fragment) for all currently
added fragments that were added with the same containerViewId and
then add(int, Fragment, String) with the same arguments given here.
So you don't need to worry about any further management since it will be taken care of for you (and be removed to free up resources). This basically means that when one is shown the other is removed. If you were to call .add() then the fragments would still be alive in the background using up resources but you don't have to worry about that since using .replace() only allows one to live at a time.
If I understand your question correctly, you need not call any method to destroy the fragments after using them. Android OS will take of them. According to the documentation, When you replace the fragment with another, the onStop() method of the fragment will be executed, and documentaed as,
The fragment is not visible. Either the host activity has been stopped or the fragment has been removed from the activity but added to the back stack. A stopped fragment is still alive (all state and member information is retained by the system). However, it is no longer visible to the user and will be killed if the activity is killed.
So the fragment will be killed by the OS when the activity is killed. Till the activity is live, fragment objects will reside in the memory.
EDT:
So, if you want to use the fragment again in future, as document suggests,
Also like an activity, you can retain the state of a fragment using a Bundle, in case the activity's process is killed and you need to restore the fragment state when the activity is recreated. You can save the state during the fragment's onSaveInstanceState() callback and restore it during either onCreate(), onCreateView(), or onActivityCreated(). For more information about saving state, see the Activities document.
Fragment are hard coded in xml can not replaced....
but when you call replace(..) then what happen ??
Ok just consider you have 3 fragment A,B,C . In primary stage A initialize in MainActivity... now you are going to call B from A using replace(....). that means A will go onPause(),onStop() state of lifecycle and B will be initialized and paced in MainActivity...same as for C then B is onPause() ,onStop() state. If you want to reuse A or B then you need to call again A or B from C using replace (..). and then A or B will reinitialize and C goes to onPause(),onStop(). But there is another way you can do this
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
hide(A);
show(B);
ft.commit();
if you use above code block then A still be in the running state of its lifecycle but not visible (just detached from UI ).. so it would be better if you need those fragment again use hide()or show() method because it is less expensive operation then reinitialize the fragment.
Given the application flow show in the graphic and textually described in the following.
Fragment 1 is the lowest fragment but not in the backstack by setting disallowAddToBackStack.
Fragment 2 is pushed onto the stack, using fragmentTransaction.addToBackStack().
A new instance of fragment 1 is pushed onto the stack.
The top most fragment (fragment 1) is popped from the stack.
Activity 2 becomes foreground.
Activity 1 becomes foreground.
Here is the generalized method I use to handle fragments:
private void changeContainerViewTo(int containerViewId, Fragment fragment,
Activity activity, String backStackTag) {
if (fragmentIsAlreadyPresent(containerViewId, fragment, activity)) { return; }
final FragmentTransaction fragmentTransaction =
activity.getFragmentManager().beginTransaction();
fragmentTransaction.replace(containerViewId, fragment);
fragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
if (backStackTag == null) {
fragmentTransaction.disallowAddToBackStack();
} else {
fragmentTransaction.addToBackStack(backStackTag);
}
fragmentTransaction.commit();
}
Problem
When activity 1 resumes in the last step the lowest instance of fragment 1 also resumes. At this point in time fragment 1 returns null on getActivity().
Question
Why is a fragment which is not the top most on the stack resumed?
If resuming the fragment is correct - how should I handle a detached fragment?
When an Activity is not showing UI and then come to show UI, the FragmentManager associated is dying with all of your fragments and you need to restore its state.
As the documentation says:
There are many situations where a fragment may be mostly torn down (such as when placed on the back stack with no UI showing), but its state will not be saved until its owning activity actually needs to save its state.
In your Activity onSaveInstanceState and onRestoreInstanceState, try saving you Fragment references and then restore them with something like this:
public void onSaveInstanceState(Bundle outState){
getFragmentManager().putFragment(outState,"myfragment", myfragment);
}
public void onRetoreInstanceState(Bundle inState){
myFragment = getFragmentManager().getFragment(inState, "myfragment");
}
Try this out and have luck! :-)
I don't see how this would happen, unless (based on how you described the steps) you've misunderstood how fragmentTransaction.addToBackStack() works: it manages which transactions are placed in backstack, not fragments.
From the android docs:
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.
So if your step 2 looked something like this in code:
fragmentTransaction.replace(containerViewId, fragment2);
fragmentTransaction.addToBackStack();
fragmentTransaction.commit();
and your step 3:
fragmentTransaction.disallowAddToBackStack()//or just no call to addToBackStack - you do not say
fragmentTransaction.replace(containerViewId, newfragment1);
fragmentTransaction.commit();
At this point, Fragment2 will be removed from the backstack, and your backstack consists of the two Fragment1 instances. in Step 4 you pop the top one, which means you should have the bottommost Fragment1 now at the top.
This explains why it is the resumed fragment if you return to the activity. But not, i'm afraid, why it is apparently detached from its activity.
Android OS can and will create and destroy fragments when it sees fit. This is likely happening when you launch Activity 2 and return to Activity 1. I'd verify for sure that it isn't the actively displayed fragment. What is probably happening is that you are seeing it do some of the creation steps for fragment 1 before it does the creation steps for fragment 2.
As for handling the detached fragments you should take a look at this page. The gist of it is that you should only be using the getActivity in certain fragment functions(Based on the fragment life cycle). This might mean that you have to move some of your logic to other functions.
I'm trying to decide and show a fragment in activity's onResume method, but in case a previously added fragment is chosen again, then the activity goes blank.
Sample code (with one fragment):
#Override
protected void onResume(){
FragmentTransaction trans = getSupportFragmentManager().beginTransaction();
trans.replace(R.id.myLayout, fragA);
trans.commit();
getSupportFragmentManager().executePendingTransactions();
}
With above code, when the activity is created for the first time, it shows fragA correctly, but in case I press Home Key and then switch back to my activity (in order to provoke onResume again), it all goes blank (seems like fragA is removed).
Is replacing a previously added fragment removes itself? or how not to loose a fragment if it is replaced by itself?
You can't replace a fragment with itself. The first half of a replace is a removal of the previous fragment at that id. Once a fragment is removed it can no longer be added or used by the fragment manager (so the add portion of the replace will not work properly).
Depending on your use case, you have two options:
Create a new fragment instead of reusing the existing instance
Use some other method to see if its necessary to replace your fragment
Finally, you probably don't need to call executePendingTransactions.
You can try:
if( !(getSupportFragmentManager().findFragmentById(R.id.myLayout) instanceof FragmentA) ) {
FragmentTransaction trans = getSupportFragmentManager().beginTransaction();
trans.replace(R.id.myLayout, fragA);
trans.commit();
}
And I assume that fragA is FragmentA class object.
Finally, I had to put a check before replacing fragments. In case, an (already added) fragment is requested for replace again, I had to check if its already added then ignore the replacement, else proceed. For example:
#Override
protected void onResume() {
if (!fragA.isAdded()) {
FragmentTransaction trans = getSupportFragmentManager().beginTransaction();
trans.replace(R.id.myLayout, fragA);
trans.commit();
//getSupportFragmentManager().executePendingTransactions(); //unnecessary
}
}
When referencing back to a created Fragment please do make sure to try adding the
fragmentTransaction.addToBackStack(null);
method right before committing so that your Fragment is resumed instead of destroyed as mentioned in the developer guides.
If you don't call addToBackStack() when you perform a transaction that removes a fragment, then that fragment is destroyed when the transaction is committed and the user cannot navigate back to it. Whereas, if you do call addToBackStack() when removing a fragment, then the fragment is stopped and is later resumed if the user navigates back.
You can find this at the end of this page.