I'm making a view whose architecture is:
A fragment has view pager that has FragmentStatePagerAdapter(adapter 1), FragmentStatePagerAdapter (adapter 1) returns a Fragment when click on Fragment it opens another Fragment that again has a ViewPager and FragmentStatePagerAdapter(adapter 2) attached to it that again returns a Fragment.
My problem is when I'm clicking on Fragment and returning by pressing back button the Fragment is blank, also when I'm using getChildFragmentManager on adapter 1, application crashing that no view found for Fragment.
Edit:
by debugging I found that FragmentStatePagerAdapter wont return fragment that was returned previously thats why I'm getting blank page
In a fragment:
viewPagerDetail.setAdapter(new ProductDetailViewPagerAdapter(getFragmentManager()));
tabLayoutDetail.setupWithViewPager(viewPagerDetail);
(if I'm using getChiildFragmentManager here it crashing application)
Inside ProductDetailViewPagerAdapter:
#Override
public Fragment getItem(int position) {
return new ViewPagerImageFragment();
}
Inside ViewPagerImageFragment: there is single imageview when I click on image view it opens a fragment that has viewpager that has adapter attach on it that also returns a fragment when I press back to fragment that has ProductDetailViewPagerAdapter the viewpager is blank
For the fragment like these kind of nested, we should see for hierarchy of the fragment either we want to see parallel or step ahead or below for step ahead or below choose getFragment manager when replacing and
getParentFragment().getFragmentManager()
for parallel fragment replacement
Happy coding!
I'm new to fragments. I have an activity that extneds FragmentActivity and uses the ViewPager to swipe between fragments.
Within one of the fragments I want to launch a new fragment that is "outside" of whats in the view pager. Is it possible to add a fragment like this or do I need to start a new activity with the fragment.
Now I have it launch a new activity but it is very slow.
Activity A
Fragment A
Fragment B
Fragment C
Activity B
Fragment D
Fragment A
So fragment A can launch acitvity B to get to fragment D but ideally it would be cool if I could just inject fragment D in Activity A
Hope that makes sense.
Yes, you can, but I strongly suggest you avoid it, unless you have a good reason to do so.
The ViewPager is (I assume) hosted in your Activity. The ViewPager obtains its views from its adapter. (A FragmentStateAdapter or similar). So you could tell the activity to change its layout (and or hide the Viewpager and show another FrameLayout) or you can simply launch another Activity that contains a single fragment. This is also fine.
Messing with the ViewPager/Adapter is usually complicated and you may waste time trying to make it work.
On the other hand, you could add the Fragment to the ViewPager's Adapter and use the getType of the adapter to return a different type of Fragment.
So you could do (pseudo code):
mPagerAdapter.addFragmentDToTheDataAtPositionZero(); //longFancyName ;)
mPagerAdapter.notifyDataSetChanged();
mViewPager.setCurrentItem(0, false);
that'd add Fragment D to the "top" of the viewpager and will switch to it.
Your Adapter then has to use an Interface to determine what type of fragment must be instantiated…
The getItem of the adapter would look like… (again, pseudocode)
#Override
public Fragment getItem(final int i) {
final FragmentTypeInterface f = yourData.get(i);
if (f.isD()) {
return FragmentD.newInstance();
} else {
return OtherFragment.newInstance();
}
}
And so forth… :)
First of all I'm sorry if this explanation seems unclear, I'm new to Android.
I have a ViewPager in main activity showing fragments added dynamically by user. Fragments are created initially on activity start up and are added to ViewPager via Adapter i.e. adapter simply returns proper fragment and as I understand correctly fragment's content is created at this time when ViewPager 'retrieves' a fragment first time.
The problem is when main activity gets restored after orientation changing all fragments are resurrected as well and when Adapter tries to return newly created by user Fragment method createView() is no longer called and it fails with NullPointerException. It seems ViewPager retains fragments attached to it initially and doesn't call createView() for newly added ones for the same position.
I have a feeling I'm missing vital point on the Fragment lifecycle. I wouldn't like to change the design. My main question is what the correct way is to return a Fragment added to ViewPage after activity is restored? Is there any way to locate recently attached fragments?
If the fragment already exists, it will be re-used. However the state of the fragment will not. You should take a look at http://developer.android.com/training/basics/activity-lifecycle/recreating.html for more information.
In particular you should look at overriding onSavedInstanceState and onRestoreInstanceState as a method to repopulate the field that is generating that nullpointerexception
To determine if an instance of a fragment has already been created you can use 'findFragmentByTag' like so:
String fragmentTag = MyFramgment.getClass().getName();
MyFragment frag = getFragmentManager().findFragmentByTag(fragmentTag);
if(frag == null)
frag = new MyFragment();
Whatever ends up being referenced in 'frag', show this to the user.
I am using a ViewPager plugged to a FragmentStatePagerAdapter. Each fragment contains a listview. In this listview I wish to display ads and make calls to a analytics server. I only want to make those calls when the user navigates to a fragment (so I cannot use the onCreateView or onActivityCreated events in the Fragment). Is there an event I can hook on to this end ?
Update
I realized that the way I am fetching my current fragment is flawe
#Override
public void onPageSelected(int page) {
this.currentPage = page;
tabsAdapter.getItem(page);
}
getItem(int position) in the pager is actually responsible for instanciating the fragments, so it would create a new unattached fragment (hence getActivity() returning null). I think I will us an approach where I keep a map of the fragments (<Position, Fragment>), i will remove the fragment from the map when destoryItem is called in the pagerAdapter.
You are right, best option is the second solution here:
http://tamsler.blogspot.nl/2011/11/android-viewpager-and-fragments-part-ii.html
so your thoughts are correct.
How about this:
http://developer.android.com/reference/android/support/v4/view/ViewPager.OnPageChangeListener.html
The onPageSelected(int) method sounds like it does what you want.
I'm getting this on some cases, in onResume(), of an activity which uses a FragmentStatePagerAdapter. When using device's back button. Not always. Not reproducible.
I'm using support package v4, last revision (8).
Already searched with google, no success finding a useful answer.
Looking in the source, it's thrown here: FragmentManager.java
#Override
public void putFragment(Bundle bundle, String key, Fragment fragment) {
if (fragment.mIndex < 0) {
throw new IllegalStateException("Fragment " + fragment
+ " is not currently in the FragmentManager");
}
bundle.putInt(key, fragment.mIndex);
}
But why is the index of fragment < 0 there?
The code instantiating the fragments:
#Override
public Fragment getItem(int position) {
Fragment fragment = null;
switch(position) {
case 0:
fragment = MyFragment.newInstance(param1);
break;
case 1:
fragment = MyFragment2.newInstance(param2, param3);
break;
}
return fragment;
}
#Override
public int getCount() {
return 2;
}
If your ViewPager is layouted inside a fragment (not an activty) :
mViewPager.setAdapter(new MyFragmentStatePagerAdapter(getChildFragmentManager()));
I had the same error here, but for another reason.
In my case I had override getItemPosition in my FragmentStatePagerAdapter. My ideia was to return the position, if the item exists, or a POSITION_NONE, if it doesn't exists anymore.
Well, my problem was the fact that when my collection got empty I returned POSITION_NONE. And that broke everything.
My fix was to return POSITION_UNCHANGED when I had an empty collection.
Hope it helps someone else.
The two key things to understand the bug are:
It happens sometimes.
It happens in onResume().
Given this information, it's likely that the ViewPager is not retaining the state of your Fragments. If you are manipulating the Fragments directly from the Activity, it could be the case that the off-page Fragment is getting destroyed and your Activity is trying to manipulate a null fragment. To retain the Fragment's state even when it is not in the current screen, the fix is pretty simple:
private static final int NUM_ITEMS = 2;
ViewPager mPager = /** instantiate viewpager **/;
mPager.setOffscreenPageLimit(NUM_ITEMS-1);
You can read about it here:
ViewPager Fragments getting destroyed over time?
Got it, the reason was, that I'm intantiating the Adapter each time in onResume().
If I instantiate the adapter only once, in the life cycle of the activity, this does not happen anymore.
This exceptions means that you are trying to attach a fragment to an activity which is no longer correct state to attach the fragments. What it means is, whenever we try to attach fragments (especially through an asynchronous call), there is a small probability that someone has pressed the back button and activity is in merge of getting destroyed while you are attaching the fragment. This is not always reproducible as its just a race condition, and might not always occur..
There are two ways to fix this:
1) This happens when you the onSaveInstanceState of your activity has been called and post to that you are trying to attach the fragment, since android wont be able to save the state of your fragment now, it will throw an exception. To overcome this and if you are not saving the state of your fragment, try using
commitAllowingStateLoss(), while committing the transaction.
2) To be very safe, check whether your activity is in correct state or not before attaching the fragment, use the following code in onPause:
boolean isInCorrectState;
public void onCreate{
super.onCreate();
isInCorrectState = true;
}
public void onPause() {
super.onPause();
if(isFinishing()){
isInCorrectState = false;
}
}
Now use this flag to check if your activity is in correct state or not before attaching the fragment.. Meaning attach the fragment iff isInCorrectState == true.
For me the reason was something else.
In my Loader.onLoaderReset() I cleared the data from the adapter. When I was leaving the app, onDestroy() caused the loader to reset, which cleared the FragmentStatePagerAdapter. I think it caused the adapter to clear all references to it's Fragments, but somehow, the FragmentManager didn't notice and threw the Exception. Doesn't seem very logical to me.
Note that for me it happened Activity.onDestroy().
Hope it helps someone.
Fragments in the ViewPager are fixed, instead of trying to replace the fragments in the adapter, try to give a different set of fragments and notifyDataSet changed, or take the advantage of FrameLayout to show another fragment over the view pager tab's current fragment.
There is my solution that works:
Swipe Gesture applied at Fragment level along with ViewPager with it's default swipe disabled