I have several fragments. I want them to come one after another as ViewPager. If i swipe right then a fragment will be destroyed storing a value "yes" and if i swipe left it will destroy storing a value "no" and next fragment will appear. I tried FragmentStatePagerAdapter but not getting desired result. I have google a lot but unable to do as I want.
Suppose I have 3 fragments 1,2,3.
1 is the first fragment. If I swipe right/left fragment 1 will destroy storing a value and fragment 2 will appear, and so on. When swiping to last fragment, a Dialog box will pop up with completion message.
Your ViewPager does not destroy your fragment, when you swipe from fragmet 1 to fragment 2. However, if you swipe from fragment 2 to fragment 3, fragment 1 is destroyed. This also applies to when you swipe from fragment 2 to fragment 1. In that case, fragment 3 is destroyed.
If you want to store a value between swipes, you should probably use the onPause callback method of the respective fragment.
Related
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.
Scenario: I have three fragments in ViewPager in activity.
Fragment One
FragmentTwo
FragmentThree
I noticed that switching from fragment one to three onPause() method is called
but when I switched from fragment one to two onPause is not called
Problem: I want to show some data in FragmentOne's TextView with a webservice on button click.I clicked that button and data is shown But I noticed when I switch from one to two and then come back to fragment one data is shown. I want to hide that data when I come back to one. Is there any callback . ?
You need to understand Viewpager first. viewpager creates fragment in advance before and keeps so that there is smooth flow when you switch, like if you are on Fragment 2. viewpager creates 1 and 3 and keeps.
and when you are on Fragment 3 it retains Fragment 1.
Anyways you can increase the limit of viewpager with this
viewPager.setOffscreenPageLimit(int num)
you can understand all the lifecylce of fragment in Viewpager by putting Logs in onPause and onResume in viewpager fragments.
Anyways coming back to your prob. you need to have custom interface like this . answer helped me too
Its happening because Fragment One is in backstack. Dont keep FragmentOne in backstack while switching to FragmentTwo and on Back press of FrgamentTwo call switchContent for FragmentOne again .
I am using a ViewPager inside a TabLayout. The ViewPager has 3 pages where each page is a fragment.
When the activity containing the TabLayout starts, the fragment callback methods upto onResume() are called for fragment1, which is as expected and fragment1 is displayed on the screen.
However, logcat shows that the callback methods upto onResume are also called for fragment2, although fragment2 is currently not being displayed on the screen. This looks odd to me since onResume should only be called when a fragment is about to become visible.
When I select fragment2, onResume is called for fragment3, although fragment3 is not being displayed. So there seems to be a pattern to this behaviour.
What could be the cause for this?
Update: The ViewPager I am using is a subclass of FragmentPagerAdapter.
If is default behavior of ViewPager to call next Fragment when ViewPager is initilized.
You need to use setOffscreenPageLimit()
setOffscreenPageLimit() sets the number of pages that should be retained to either side of the current page
Default value is 1 so next Fragment to the left and to the right will stay in memory.
To prevent from calling next Fragment you need to set 0 value to OffscreenPageLimit
viewPager.setOffscreenPageLimit(0);
on the ViewPager object.
EDIT:
But i have checked by setting limit to 0.
setOffscreenPageLimit(0) will not work now. when you set limit to 0 you can see below warning in LogCat:
Requested offscreen page limit 0 too small; defaulting to 1
So i advise you to either call setOffscreenPageLimit(2) which will keep all your 3 Fragments in memory otherwise don't call setOffscreenPageLimit(int limit) on ViewPager.
Two things contribute to this behavior:
Fragments are not required to have a UI, in which case it is never "visible" on screen. Basically, if a Fragment is attached to an Activity, its lifecycle methods will be called as appropriate.
ViewPager loads items to either side of the item that is currently displayed. This is in order to have content to show as the user scrolls the page with his finger. By default the off screen page limit is 1, which means that when your first fragment is the current item, the second fragment is loaded off screen in preparation for scrolling.
You can always check which item is displayed by the ViewPager using getCurrentItem(). If you are having problems because the fragment are destroyed and recreated needlessly when they go beyond the off screen page limit, you can increase the page limit with setOffscreenPageLimit().
I have a fragment that hosts a ViewPager with 3 fragments, 2 of them contain ListView (not inherits FragmentList)
The problem is:
If I click on one of the items in one of the list the application navigates me correctly to a new fragment, but, if I press the back button and go back to the ViewPager, a can see a blank fragment, only the first fragment who didn't have ListView is created, none of the other fragments are displayed, nor even their onStart is called
What's wrong? I suppose the fragment is not attached again, how can I solve this issue?
I have a custom Viewpager in which it disables the touch events. So I have buttons 'Next' and 'Back' that control the viewpager. My question is how to pass data or bundles between the fragments in the viewpager. Normally it would work but sense the fragments are created even though they are not shown. That's because of the viewpager slide effect, it has to make the fragments ahead and before for the effect to work. So that means I can't use bundles since the fragment is already created. This is what I'm trying to do
Fragment 1 -> Fragment 2 -> Fragment 3
Fragment 1 is created and so is Fragment 2. When I press 'Next' Fragment 2 is shown. I want to pass a bundle to Fragment 3 when I press 'Next' again but Fragment 3 is already created so it won't work.
Another way I thought of is to call a method in each Fragment when the Viewpager sets it as its current Item.
Why don't you create an interface that all of your fragments implement? This interface will have two methods: getParameterData() and setParameterData(). In your ViewPager, when they press next or previous, call getParameterData() on the current fragment, then call setParameterData() on the fragment to be displayed.
You could share/pass your objects between fragments by holding them in the host activity.