CONSTRUCTION
I've got Activity that holds a "path" made of Fragments.
The User goes from Fragment1 to Fragment2 and then to Fragment3 filling up the required informations. Nothing fancy here just plain backStack and .replace made on Fragments.
QUESTION
How should I retain that information when orientation changes to get my backStack back the way it was before orientation change?
IDEAS
The only idea I have is to insert into saveInstanceState the last visible Fragment and recreate things from there but it feels really hacky and I think in the long run it's going to make some major problems.
/////////////UPDATE//////////////
It looks like nowadays Android is capable of doing it on its own as long as you are following the guidelines provided by ARTICLE
The backstack itself is saved and loaded automatically with the activity.
Here's an article how Android does save and load activity and fragment states.
What you should care of is implementing the same logic of saving and restoring states for each fragment.
Related
As the title suggests, I want to retain my fragments. I have enforced my app orientation to always be in landscape mode in the manifest file so that there will be no rotations.
I have read:
Understanding Fragment's setRetainInstance(boolean)
and
Why use Fragment#setRetainInstance(boolean)?
However, I am not sure if they apply to my situation.
My project consists of a ViewPager with swipe tabs. How can I ensure that the fragments used in the ViewPager are the same ones as created when the MainActivity first starts? Would I use the same tagging method and findfragment by tag?
Additionally, where would it be best to check for the tagged fragment, else create a new fragment?
Just a side question related to ViewPager: what can I do to immediately create all fragments used in the ViewPager when the mainactivity is started, rather than to wait for a swipe event to occur?
To answer your last question view pager will by default create the fragments around the current fragment so you don't need to worry about that part. What I would recommend is let the view pager manage your fragments for you rather changing the behaviour since you might face performance issues.
SetRetainInstance simply keeps the instance of your fragment when its detached so it's up to you to assess whether you need to use it or not.. is there anything you want to maintain about that fragment? if not then do not use it, free your memory as much as possible.
For the last question, why do you want the same fragments created from the first time to be retained ? all the time? if you NEED to do that then rethink your structuring. gracefully recreate your fragments and maybe have some caching of your data on another layer if that is what you are worried about.
When rotating the screen my nested fragment is shown but for some brief moments, the parent fragment is also shown.
I have my MainActivity that has a FrameLayout with ID activity_base_container.
I'm doing this when my activity starts:
Fragment initialFragment = getInitialFragment();
mFragmentManager.beginTransaction()
.add(R.id.activity_base_container, initialFragment, initialFragment.getClass().getSimpleName())
.commit();
That initialFragment initial fragment is responsible to check some conditions and depending them will launch one of two possible fragments:
fragmentManager.beginTransaction().replace(R.id.activity_base_container, fragment, fragment.getClass().getSimpleName()).commit();
Lets assume it launches FragmentF (whit a root FrameLayout with id fragment_f_root). This fragments layout has a set of options. When the user clicks one of those options, the corresponding fragment is created and is launched like this:
//The example here is an option that displays a google map.
fragment = FragmentMapMultipleActivity.newInstance();
fragmentManager.beginTransaction()
.replace(R.id.fragment_f_root, fragment)
.addToBackStack(fragment.getClass().getSimpleName())
.commit();
At this point all is working as expected. The problem is when I rotate the screen. FragmentF appears briefly and then immediately FragmentMapMultipleActivity, the nested fragment, appears.
Is it possible after rotating the screen show only the nested fragment or I should change my "architecture" to something else?
should change my "architecture" to something else?
Probably, you should.
The brightest Android-minds from Square are even advocating to avoid simple fragments everywhere it's possible: Advocating Against Android Fragments
Nested fragemnts, in its turn, increase complexity exponentially. The only good pattern of using them I've seen so far is ViewPager with it's FragmentPagerAdapter. In majority of other cases, consider using Custom Views instead.
It keeps your app's lifecycle cleaner and more predictable.
I don't think you can do much with this blinking you see, apart from:
setRetainInstance(true) and avoid full re-creation of the Fragment in Activity, so you keep you fragment's data during change of the configuration (and then pass same retained fragment to the fragment manager)
keeping layouts as lightweight as possible
avoid re-creation of already initialized variables
keep onViewCreate() as lightweight as possible
Good luck!
Scenario:
I have a fragment which has a ViewPager which contains 5 instances(different) of a single Fragment with different values, each having a listivew that contains some sort of items.
Problem:
The flow goes smooth when I click an item of listView(say on page1) but the moment I come back from there on pressing back (overridden OnBackPressed in the main_activity (will discuss later)), the viewPager fails to load the subFragments.
But when I switch to the 2nd or 3rd page, it gets displayed, and on going back to 1st page, it now gets displayed.
OnBackPressed():
I am maintaining a manual stack here. When I click on an item of ListView, the current Fragment Instance (of the parent Fragment ofcourse) goes into stack. And when user comes back , that instance gets popped off the stack and I replaces it on the activities FrameLayout container.
References:
Fragments not getting recreated by FragmentStatePagerAdapter after coming back to the main Fragment instance
Guys, I am really pissed off here, please help me out.
Frankly, I haven't worked much with fragments.
But it seems like the page is being thrown off the memory every time you switch to other pages. I am not sure but if there is a way for android to manage this and keep the page in its memory persistently, it might solve the problem
Finally I am able to get a workaround for this issue, which included two things:
while replacing the fragment make a call to
ft.replace(R.id.content_frame, frag).addToBackStack(null);
while initiating the ViewPager, the fragment manager to be used is :
mAdapter = new myAdapter(getChildFragmentManager());
Actually the problem is that, android fails to recognise and load the older instance of the fragment unless you explicitly add that instance to the backstack. So after adding it to BackStack, there is practically no need to maintain your own manual Stack, but you still can do that.
I have looked around and found variations of this question, but all of the answers seem to be ugly hacks. Is there no easy and proper way to achieve this?
Say for instance I have Activity A, which has a FrameLayout that can hold one fragment at a time. Lets say that when the Activity is first started it loads Fragment A into the FrameLayout, which consists of a ListView. When an item is selected in Fragment A it starts up Fragment B. The way I am currently doing this is by simply hiding Fragment A and then adding Fragment B since this preserves Fragment A's state. I am of course also adding this fragment transaction to the backstack.
So now Fragment A exists on the backstack. Say now I go back to my Android home screen and go to another app. While I am doing this, the Android system decides to destroy my application because the system needs more memory. When I navigate back to my application, how am I supposed to properly restore the state of Fragment B, and Fragment A which is currently on the backstack.
I cannot use setRetainInstance() since it does not work for Fragments placed on the backstack.
Essentially what I am trying to do is restore the backstack to exactly how it was before my application was forcefully closed. So Fragment A should be on the backstack (but not showing), and Fragment B should be currently showing. If I hit the back button, it should properly pop Fragment A off the backstack.
Some notes
Since the application was forcefully closed, it's savedInstanceState != null. Same thing holds for the fragments.
I'm not quite understanding this fragment lifecycle business.
I have a pretty standard 3 page horizontal slider view Pager layout for a "view details" section of my app. I start my app on the middle page of the three. My FragmentActivity sets the page to page 1.
mPager.setCurrentItem(1); //default to center page, current data view fragment
I've been using the FragmentStatePagerAdapter because using the FragmentPagerAdapter crashed my app at times, when coming back from a suspended state for example, and this was the quickest way to work around that for now. Seems to work but I suspect the State aspect is what might be the cause of my problem here, maybe.
So at first I thought that I would have each fragment do the work of getting data from a rest service and then showing it in a list, but I'm not so sure any more.
I tried running a unique async task to fetch data in each of the fragments onCreateView events.
Then after reading more on the fragment lifecycle I switched to onCreate, having noticed that the onCreateView was being called quite heavily, which in turn made for a greedy app that too often requested data over the wire.
Switching to onCreate hasn't changed anything. OnCreate is still geting called just as much as onCreateView for the 2 adjacent fragments.
The odd thing is that the fragment that I set to be the first one to display in Fragment Activity only gets the onCreate called the one time.
Something doesn't feel right here.
Right now I'm thinking that I should have the parent fragment activity declare and call all the async tasks to fetch the data that I need to display in the fragments.
Set the results of the async calls in an object owned by the parent fragment activity and then have the fragments use the object contained by the parent to create the list view etc.
But what if the async tasks started by the parent activity don't finish before each fragments onCreateView is called and the object contained by the parent isn't ready yet.....
signed, confused and frustrated
ViewPager is quite zealous in shutting down things it isn't currently using, and this is exactly what is happening here. The default behaviour is for ViewPager to "keep around" one page either side of the page being viewed, and destroy the rest. Hence in your 3-page view, page 3 gets destroyed when selecting page 1, then when page 2 is reselected page 3 is recreated. As you've noticed, page 2 only has onCreate(..) called once because it is always adjacent to, or is, the currently selected page.
To solve this, simply set ViewPager.setOffscreenPageLimit(2). Then the ViewPager will keep all your Fragments. Obviously this isn't a good idea for a large number of Fragments, but for your case it should be fine.
#Espiandev's solution will work for your current case, but you're right that your state is the issue. You should use the setArgument and/or onSaveInstanceState methods to save your Fragment's state (which shouldn't be too hard, since e.g., a response from the server can usually be represented as a String), and then use getArgument and/or the Bundle passed in onCreate to restore it.
Alternatively, you could have your Activity do the server fetches, and then call setArgument for each of your fragments, and check the arguments inside your Fragment to determine if your data has arrived yet (and if not, potentially display a loading state of some kind).
If you care at all about screen orientation change, this related question will also be useful to you.