An Activity uses a FragmentPagerAdapter with two Tabs (and a fragment for each tab).
At first, only the Home fragment is visible, and the Run fragment is not.
tabsPageAdapter = new TabsPagerAdapter(getSupportFragmentManager());
...
viewPager = (ViewPager) findViewById(R.id.pager);
...
viewPager.setAdapter(tabsPageAdapter);
The FragmentPagerAdapter looks a bit like this :
class TabsPagerAdapter extends FragmentPagerAdapter {
public TabsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int index) {
switch (index) {
case 0: {
return Fragment.instantiate(MainActivity.this, HomeFragment.class.getName());
}
case 1:
return Fragment.instantiate(MainActivity.this, RunFragment.class.getName());
}
return null;
}
}
When an Async Task in the Home Fragment succeeds, it notifies the Activity to show the Run Fragment.
viewPager.setCurrentItem(1);
This makes the RunFragment visible, but it calls none of the lifecycle methods :
onCreate (which makes sense, since it has already been created before)
onResumed
Unfortunately, I need some code in the RunFragment to run at this moment (it can not run before, since it depends on side effects of code that was run in the HomeFragment.)
I tried :
using the lifecycle methods (none seem to be called)
keeping a reference to the RunFragment in the MainActivity ; this does not work, as the reference to the RunFragment ends up being "null" from time to time (or it is not null, but its reference to getActivity() is null)
How would I attack this ?
Related
Okay i'll try and make this as clear as possible. I have a Fragment called CheckerManager which contains a ViewPager. This ViewPager will allow the user to swipe between 3 Fragments all of which are an instance of another Fragment called CheckerFragment. I'm using a FragmentPagerAdapter to handle paging. Here's how it looks
private class PagerAdapter extends FragmentPagerAdapter {
CharSequence mTabTitles[];
public PagerAdapter(FragmentManager fm, CharSequence tabTitles[]) {
super(fm);
mTabTitles = tabTitles;
}
#Override
public Fragment getItem(int position) {
switch(position) {
case 0:
return CheckerFragment.newInstance(MainFragment.DRAW_TITLE_LOTTO);
case 1:
return CheckerFragment.newInstance(MainFragment.DRAW_TITLE_DAILY);
case 2:
return CheckerFragment.newInstance(MainFragment.DRAW_TITLE_EURO);
default:
return null;
}
}
#Override
public CharSequence getPageTitle(int position) {
return mTabTitles[position];
}
#Override
public int getCount() {
return 3;
}
}
I know that the ViewPager will always create the Fragment either side of the current Fragment. So say my 3 CheckerFragments are called A, B and C and the current Fragment is A. B has already been created. But my problem is that even though I am still looking at Fragment A, Fragment B is the 'active' Fragment. Every input I make is actually corresponding to Fragment B and not A. The active Fragment is always the one which has been created last by the ViewPager.
I've looked at quite a few things to see if anyone has had the same problem but i'm finding it difficult to even describe what's wrong. I think it's something to with the fact that all of the ViewPagers fragments are of the same type ie - CheckerFragment. I have a working implementation of a ViewPager inside a fragment elsewhere in the application and the only difference I can tell is that each page is a different type of Fragment.
Any help would be appreciated!
*EDIT
PagerAdapter adapter = new PagerAdapter(getChildFragmentManager(), tabTitles);
ViewPager viewPager = (ViewPager)view.findViewById(R.id.viewPagerChecker);
viewPager.setAdapter(adapter);
I feel pretty stupid but I found out what the issue was. In my CheckerFragment I would call getArguments() to retrieve a String extra and I would use this to determine how to layout the fragment. Problem was I made this extra a static member of CheckerFragment. So every time a new Fragment was created it was using the most recent extra.
Moral of the story - Don't make your fragments extra a static member if you plan on making multiple instances of that fragment.
I'm testing my app with 'destroy all activities as soon as user leaves it' to simulate the OS killing my app.
In my main activity, in onCreate, I instantiate all the fragments, add them to a list and then:
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager(), fragments);
mViewPager = (ViewPager) super.findViewById(R.id.pager);
mViewPager.setAdapter(mSectionsPagerAdapter);
Here is the adapter code:
public class SectionsPagerAdapter extends FragmentPagerAdapter {
private List<Fragment> fragments;
public SectionsPagerAdapter(FragmentManager fragmentManager, List<Fragment> fragments) {
super(fragmentManager);
this.fragments = fragments;
}
#Override
public Fragment getItem(int position) {
return fragments.get(position);
}
#Override
public int getCount() {
return fragments.size();
}
#Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0: return getString(R.string.section_one);
case 1: return getString(R.string.section_two);
case 2: return getString(R.string.section_three);
case 3: return getString(R.string.section_four);
}
return null;
}
}
Now, the problem (crash) lies here, in an action bar item:
case R.id.action_refresh:
PostsFragment fragment = (PostsFragment) mSectionsPagerAdapter.getItem(mViewPager.getCurrentItem());
fragment.reloadDataFromServer();
Say the activity was opened, then destroyed on the back button. When I return to this activity and press the refresh action item, the app crashes. Why? When the activity is created again, it creates a new pager adapter, with all new 4 fragments. But onCreate of these fragments is never called, none of the members are initialized, so the reloadDataFromServer fails loading into a listview that hasn't been initialized yet.
HOWEVER, the onCreate of the previous referenced fragments IS called, but we no longer have a reference to them because we recreated the FragmentPagerAdapter with new fragments. This is driving me INSANE! Why is onCreate not called for the new fragments?
In case someone has problems with this, I'll explain my solution. Basically what happens is fragments that were created before are restored on recreation of the activity after a destruction. This may be a duh moment for some of you.
My problem is essentially having incorrect references to fragments.
First, I changed the setOffscreenPageLimit to the full (#tabs - 1). This means all fragments are created at the start and held in memory. I'll explain why this helps later.
This means in onSaveInstanceState, we can use putFragment on all 4 fragments with the outState Bundle.
In create, if savedInstanceState is null, we can create all 4 fragments from scratch. Otherwise, you can use getFragment on all 4 fragments and place them into the new pager adapter to hold as reference.
You may ask why I set setOffscreenPageLimit to max. I had problems with figuring out which fragments to save with putFragment. isAdded() did not seem to always work properly, neither did isResumed(), so it was easier to just save all of them because we know all 4 were created and were in the fragment manager at all times.
Currently, with a FragmentActivity, I toggle among 2 type of Fragments using the following code.
private void toggle() {
Fragment oldFragment = getSupportFragmentManager().findFragmentById(R.id.content);
Fragment fragment = null;
if (oldFragment instanceof ColorFragment) {
fragment = new ViewPagerFragment();
} else {
fragment = new ColorFragment(android.R.color.black);
}
getSupportFragmentManager().beginTransaction().replace(R.id.content, fragment).commitAllowingStateLoss();
}
2 Fragments are being toggle.
ColorFragment - A simple fragment which fill up its background with solid black color.
ViewPagerFragment - A fragment contains ViewPager. User can swipe between a purple color fragment, and a blue color fragment.
The code which responsible for swiping purple and blue color fragments are as below.
private static class MyFragmentPagerAdapter extends FragmentPagerAdapter {
public MyFragmentPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public int getCount() {
return 2;
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new ColorFragment(android.R.color.holo_purple);
default:
return new ColorFragment(android.R.color.holo_blue_bright);
}
}
}
However, I encounter the weird behavior during toggling.
Black color fragment was shown.
Toggling.
View pager, which can swipe between purple and blue fragments shown.
Toggling.
Black color fragment was shown.
Toggling.
Nothing shown, as MyFragmentPagerAdapter's getItem is not being triggered.
I think my situation is similar to FragmentPagerAdapter getItem is not called
However, I prefer not to use FragmentStatePagerAdapter, because of the cost of potentially more overhead when switching between pages.
Any workaround to overcome this problem?
I include a complete workable source code to demonstrate this problem : https://www.dropbox.com/s/jok9tz5ktvfcteo/viewpagerbug.zip
Any workaround to overcome this problem?
I've downloaded your code and the problem appears because you don't handle those Fragments right. Most precisely you use nested Fragments in the ViewPager based Fragment and for that ViewPager you create the adapter like this:
MyFragmentPagerAdapter myFragmentPagerAdapter = new MyFragmentPagerAdapter(this.getFragmentManager());
Instead, you should be using getChildFragmentManager() to bind the nested fragments:
MyFragmentPagerAdapter myFragmentPagerAdapter = new MyFragmentPagerAdapter(this.getChildFragmentManager());
Also, you shouldn't pass data through a constructor to a Fragment as that data will not survive a configuration change and bad things will start to appear. Use a Bundle instead.
Global working tested solution.
getSupportFragmentManager() keeps the null reference some times and View pager does not create new fragment instance.Since it finds reference to same fragment. So to over come this use getChildFragmentManager() solves problem in simple way.
Don't
new PagerAdapter(getSupportFragmentManager(), fragments);
Do
new PagerAdapter(getChildFragmentManager() , fragments);
Simple use FragmentStatePagerAdapter instead of FragmentPagerAdapter
or
you can use new MyFragmentPagerAdapter(this.getChildFragmentManager())
Hope it will help you :)
In my case I was correctly calling
MyFragmentPagerAdapter myFragmentPagerAdapter = new MyFragmentPagerAdapter(this.getChildFragmentManager());
but then in the nested fragment I was trying to replace the container fragment with another one by using:
getFragmentManager()
You need to go to the activity and call
getActivity().getSupportFragmentManager();
In my cases it worked after add this to my FragmentPagerAdapter:
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
and I also used getChildFragmentManager() like Luksprog said
I have a ViewPager with 3 Fragments and my FragmentPagerAdapter:
private class test_pager extends FragmentPagerAdapter {
public test_pager(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int i) {
return fragments[i];
}
#Override
public long getItemId(int position) {
if (position == 1) {
long res = fragments[position].hashCode()+fragment1_state.hashCode();
Log.d(TAG, "getItemId for position 1: "+res);
return res;
} else
return fragments[position].hashCode();
}
#Override
public int getCount() {
return fragments[2] == null ? 2 : 3;
}
#Override
public int getItemPosition(Object object) {
Fragment fragment = (Fragment) object;
for (int i=0; i<3; i++)
if (fragment.equals(fragments[i])){
if (i==1) {
return 1; // not sure if that makes a difference
}
return POSITION_UNCHANGED;
}
return POSITION_NONE;
}
}
In one of the page (#1), I keep changing the fragment to be displayed. The way I remove the old fragment is like this:
FragmentManager fm = getSupportFragmentManager();
fm.beginTransaction().remove(old_fragment1).commit();
And then just changing the value of fragments[1]
I found that I cannot really add or replace the new one or it will complain the ViewPager is trying to add it too with another tag... (am I doing something wrong here?)
All the fragments I display have setRetainInstance(true); in their onCreate function.
My problem is that this usually works well for the first few replacement, but then when I try to reuse a fragment, sometimes (I have not really figured out the pattern, the same fragment may be displayed several times before this happens) it will only show a blank page.
Here is what I have found happened in the callback functions of my Fragment I am trying to display when the problem happens:
onAttach is called (but at that time, getView is still null)
onCreateView is not called (that's expected)
onViewStateRestored is not called (why not?)
onResume is not called (I really thought it would...)
If it changes anything, I am using the support package, my activity is a SherlockFragmentActivity
EDIT (to answer Marco's comment):
The fragments are instantiated in the onCreate function of the Activity, I fill an ArrayList with those fragments:
char_tests = new ArrayList<Fragment>(Arrays.asList(
new FragmentOptionA(), new FragmentOptionB(), new FragmentOptionC()));
The I pick from that list to set fragments[1] (that's all done in the UI thread)
I fixed this by changing test_pager to extends FragmentStatePagerAdapter instead.
I am still confused as to what PagerAdapter should be used depending on the usage. The only thing I can find in the documentation says that FragmentPagerAdapter is better for smaller number of pages that would be kept in memory and FragmentPagerStateAdapter better for a larger number of pages where they would be destroyed and save memory...
When trying to do (fancy?) things with Fragments, I found FragmentStatePagerAdapter is better when pages are removed and re-inserted like in this case. And FragmentPagerAdapter is better when pages move position (see bug 37990)
I have following issue. I have ViewPager and FragmentPagerAdapter for it.
All I need to do is call some method from my Fragment which is in ViewPager when this page was selected.
I tried to keep all my Fragments in List inside my adapter, but the problem is that when I rotate my device Adapter use previous fragments. New fragments were created after rotation and I have list of them, but I don't now how to get access to previous fragments. I have references to new fragments only.
Here is my adapter:
public class MainPagerAdapter extends FragmentPagerAdapter {
private List<Fragment> fragmentList;
public MainPagerAdapter(FragmentManager fm) {
super(fm);
fragmentList = new ArrayList<Fragment>();
fragmentList.add(new TaskPageFragment());
fragmentList.add(new HistoryFragment());
fragmentList.add(new TestFragment());
}
#Override
public Fragment getItem(int i) {
return fragmentList.get(i);
}
#Override
public int getCount() {
return 3;
}
}
Of course when I trying to access to fragment which was only created like an object, I can't get access to Activity Context.
Fragment fragment = pagerAdapter.getItem(i);
if (fragment instanceof SelectionListener) {
((SelectionListener)fragment).onTabSelected();
}
Here is onTabSelected() method call is shown. It's my interface which I implemented to each fragment in ViewPager and when it gets called after screen rotation I get null Context
Device configurations can change during runtime (such as screen orientation). When this happens the Activity is restarted. This is done so your activities can adjust to match the new device configuration, and since fragments are within Activities they are also 'destroyed'.
However your issue may be solved with something simple, since from what I understand from your question you are not looking for UI configuration changes and assuming you are using API 11+.
public void setRetainInstance (boolean retain)
Since: API Level 11
Control whether a fragment instance is retained across Activity re-creation (such as from a configuration change). This can only be used with fragments not in the back stack. If set, the fragment lifecycle will be slightly different when an activity is recreated:
onDestroy() will not be called (but onDetach() still will be, because
the fragment is being detached from its current activity).
onCreate(Bundle) will not be called since the fragment is not being
re-created.
onAttach(Activity) and onActivityCreated(Bundle) will
still be called.
public MainPagerAdapter(FragmentManager fm) {
Fragment frag = null;
super(fm);
fragmentList = new ArrayList<Fragment>();
frag = new TaskPageFragment();
frag.setRetainInstance(true);
fragmentList.add(frag);
frag = new HistoryFragment();
frag.setRetainInstance(true);
fragmentList.add(frag);
frag = new TestFragment();
frag.setRetainInstance(true);
fragmentList.add(frag);
}