Can I tell FragmentTabHost to not destroy fragments(views) when I switch tabs? In one of the fragments I fetch some data from the Internet (or from a local database, depending on the situation), which takes a bit of time. I want to always keep this fragment in memory when it's posible.
I like the way ViewPager handles it with setOffscreenPageLimit() set to something bigger than 1.
A better solution would be to use a retained fragment without UI for fetching data and posting it to other fragments when data is there. The logic would be like this. Every fragment asks the retained fragment for data. If data is not there, they show "loading" state. If data is there, they show the data. If you want to have an event based communications between fragments, instead of calling fragments through interfaces, you can have a look at Otto event bus.
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.
I have created a tabbed android application using android.support.v4.view.PagerAdapter.
There are about seven tabs in the application and I plan to add more. Each tab contains a lot of controls (TextView, Spinners, Toggle buttons, Check boxes etc.)
On the first tab there is a drop down to select a profile. The user can 'Load' or 'Save' a profile he wants.
A profile contains data for all the controls in the tabs and I need to update the UI controls in all the tabs.
I have all the data loaded from the profile but the UI controls are not getting updated.
There is a 'UpdateUI' function which calls 'set' functions (setText, setChecked etc. for individual controls after finding its view by ID).
I was informed that only three tabs (Previous, Current and Next) are kept in memory so I wrote the application such that the 'UpdateUI' function is called to set UI data only when user swipes to that particular tab (figuring out the active fragment).
Using DDMS logs I saw that the data loaded was proper but the 'setText' or 'setXXXXX' function does not update the fragment tab.
I have also checked several possible issues:
Possibility of 'OnTextChanged' or an 'OnListener' updating the data again.
Made sure 'UpdateUI' is called from UI thread.
Using notify data change and redrawing UI to make sure UI is updated.
I am a novice Java/Android programmer. Please point me in the right direction.
viewpager.setOffscreenPageLimit(size);
you can instantiate all your fragments by setting limit then you can update all widgets inside other fragments.
If my understanding of Android Fragment management is right, once the fragment becomes invisible for user (say some other fragment completely overlayed it or in your case you change tabs) Fragment goes through onPause and possible onStop lifecycle stages, this mean it's kind of hybernated and can't be changed before it get's visible. viewpager.setOffsetPageLimit(size) tells the fragment manager (or rather pageAdapter) how many fragments should be kept hybernated, and I doubt it playing with this will change anything, but let me know if it's, because otherwise the solution may be more complicated.
What I'd do is recreate a fragment every time user gets to see it and pass your profile data to it's constructor (or following better practice newInstance() static method), it will in fact save memory since keeping many fragments there may be overwhelming. Alternatively you can check what profile is chosen everytime fragment is calling it's onResume, and update your controls there.
I have an activity with a ViewPager with a variable number of fragments (tabs).
Upon start the activity checks if the associated (complex) data has been loaded. If it hasn't it shows a progress bar view and starts an AsyncTask which fetches the data. Depending on the data the activity creates a number of fragments (tabs) and gives each fragment a sub set of the data.
I currently hold references to the fragments (I know that it is discouraged) and I run into all sorts of problems when the fragments gets reused - I'm giving the data to the wrong instance of the fragment.
So, is there an "android way" of solving this problem?
I run into all sorts of problems when the fragments gets reused
Fragments usually don't get reused in a ViewPager. This is not like an AdapterView where rows get recycled. Using FragmentPagerAdapter or FragmentStatePagerAdapter, a fragment represents one and only one page.
I re-instantiate the ViewPager each time (but the fragments get reused?)
Ah. That's a slightly different problem.
The stock implementations of FragmentPagerAdapter and FragmentStatePagerAdapter make a couple of assumptions:
They are in complete control over the fragments, particularly in terms of running the transactions to add and remove them from the UI
That those fragments will only ever be used by one "logical" ViewPager (IOW, recreating that ViewPager for a configuration change is fine, but that' pretty much it)
Complicating matters is that these adapters store the fragments under certain tags, and therefore if those fragments still exist in those tags, those existing ones will get used, instead of new ones being created.
So, is there an "android way" of solving this problem?
It's unclear from your question why you even need to "re-instantiate the ViewPager". I'm assuming that this is tied to some sort of refresh operation, or something else that is forcing you to go through the process described in your second paragraph.
You could give my ArrayPagerAdpater a try, as it is friendlier about external agents mucking about with the fragments. Since you control the fragments' tags, you can always be certain that you are working with the right fragment -- rather than caching them yourself, just retrieve the right one and manipulate it.
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.
In my application I have a FragmentActivity that uses a FragmentViewPager. The Fragments have a quite complex structure of views with ListViews and Adapters. The FragmentViewPager appears to destroy the Fragments that are out of sight, and to recreate them if the user swipes back to it. This leads to all member variables are cleared that hold the lists and adapters with all content, so the Fragment is empty if it comes back to the top.
My question now is: How can I preserve these data? If I'm not mistaken, I have to save and resume the list with the content the adapter works on. When and where should I save it?
Is it a good idea to save the data in the FragmentActivity or in a helper singleton class outside the activity?
How can I preserve these data?
Your data is already "preserved". You loaded it from somewhere originally from some data model. Load it again.
If there are changes the user is making on-screen to the data, you need to be persisting that to your data model as the user makes the changes. This is no different than dealing with, say, a RatingBar in a ListView row.