I have a view pager inside a fragment. Inside the inner fragment i have to show animation when the fragment is visible. i checked this answer and tried setUserVisibleHint and OnPageChangeListener both this are called before onCreateView and gives null pointer exception. how can i find when Fragment becomes visible in ViewPager so that i can start animation.
#bill gates, viewpager is the thing, in that both page (Current page and next or previous page) both are prepare simultaneously itself, so when you slide the current page two pages are visible to user. that a awesome function of viewpager. thanks.
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So I have a fragment inside a viewpager which is contained inside a fragment which is getting initialize'd as shown in the debugger but doesn't have it's onCreate,onCreateView or any such methods being called. The activity containing has a bottom navigation view and contains 4 such fragments and this issue is only happening in 1 such fragment.
All these fragments and viewpagers and fragments inside them are created on the oncreate of the activity. If I move the logic to create the fragment to when a bottom tab is clicked, this issue gets solved on.
How is this possible ?
Only the currently active fragment and the two directly adjecant fragments are created when the viewpager is first shown. so the fragment for the first page, the fragment for the page shown if you "scroll to the left" and the fragment for the page shown when you "scroll to the right". the 4th fragment will be created when it is put in the next adjecant position.
so if you have fragments a,b,c,d in a viewpager like -a-[b]-c-d- where b is the first visible page, only a,b and c will be created at startup. when you scroll to c -a-b-[c]-d- onCreate for fragment d will be called.
You can control number of pages/fragments preloaded when you launch your activity by setting it's off Screen Page Limit on your view pager adapter. like this
mViewPager.setOffScreenPageLimit(limit)
If you set limit to 0 than only first fragment would be load.
https://spotandroid.com/2016/11/23/android-tricks-viewpager-and-offscreen-tabs/
https://techcodegeek.wordpress.com/2015/06/23/android-viewpager-and-performance-improvements/
Need more detail to know your issue.Issue which you are facing is not understood with information you have provided.
I used the wizard to create an tabbed Activity which contains an FragmentPagerAdapter, in the getItem() function I tried to return my own fragments as follows:
However when the App runs and the view is in the first tab, I found it actually goes through the onCreateView() function in both Fragment and Fragment2(known from println() in onCreate() & onCreateView()), and when I swipe to Fragment2, it prints Fragment3. and when swipe to Fragment3, it prints nothing.. and after that I swipe back to Fragment2, It prints Fragment1.
What's wrong with it?
Thats is how a FragmentPagerAdapter is supposed to work. It created the Fragment in selected position and also the previous position and next position. This is so that when you move from one fragment to another through swipe the next fragment is ready so that it can be animated into the view. You can read about it below.
http://developer.android.com/reference/android/support/v4/app/FragmentPagerAdapter.html
I have a viewpager and a pagerAdapter which inflates a custom view and adds it to the collection. After setting up the viewpager and pageradapter, I proceed to get some data which I now want to display in one of the custom views. However I observed that the pagerAdapter.instantiateItem is not being called by that time. How can I get the viewpager to start instantiateItem right away?
instantiateItem is called when the viewPager calls the getItem method. When the viewPager is first displayed, getItem is called for the currently displayed tab and the following tab.
Could you provide a code snippet for further details ?
I'm using a ViewPager in my app. There are three fragments inside the PageAdapter that is set in the ViewPager. All works perfectly fine and I can switch between all three fragments. I have 3 buttons that allow me to switch between adapters 1 to 3. The problem is noticed when I click buttons 1 and 3 at the same time. Here's what happens:
Fragment 1 - Fragment 3
onAttach
onViewCreated
onResume
onPause
onAttach
onViewCreated
onResume
onPause
As you can see from above, the second fragment is never paused and therefore never resumed. Both fragments modify the same recycler view onResume so with the behaviour above I end up with the incorrect state of my recycler view.
Any thoughts on why this might be happening and how I can fix this?
A ViewPager loads (by default) the current page, the previous page and the next page, since you have only 3 pages the second fragment is always resumed.
the solution is to set up a OnPageChangeListener and modify the recycler view in onPageSelected instead in onResume
I use the viewpager and fragment, the adapter is FragmentStatePagerAdapter, fragment's layout i use is SwipeRefreshLayout(22.0.0)+ListView, the ViewPager's setOffScreenPageLimit is 1, Just think i click in all the fragment, current is fragment 1 tap the refresh then click to fragment 3 then go back! the ghost is come up!