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Here are some tips that I follow now while using fragments in my activities:
First you would like to achieve something like this:
https://moqups.com/abhsax130778@gmail.com/lc0ZOERO/p:a5d7b55eb
Then there are scenarios like:
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Scenario 1:
1. Suppose there is a fragment on an activity and a button on it. You click on a button and another fragment opens.
2. From there, you press on back/return button and you come to first fragment.
That is easily done using back stack.
Now you want to do the same using swipe. I mean coming from second fragment to the first using the swipe and not the back/return button.
You usually do it with a backstack, while replacing the fragment 2 with fragment 1 in the transacton when opening fragment 2 from fragment 1:
FragmentManager manager = ((FragmentActivity) this).getSupportFragmentManager();
manager.popBackStack();
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Scenario 2:
1. There are 4 tabs on action bar activity, and on each there is a fragment.
2. You click on a button on fragment 1 on tab one and it replaces with fragment 5 (while 2, 3 and 4 are on their tabs respectively).
you move to tab 2 and there is fragment 2, and when coming to tab 1, still there is fragment 5.
You left swipe on fragment 5 and come to fragment 1 remaining on tab 1 and this state is also maintained.
This you can do without transactions by having stack of fragments for each of the tab and pop when onBackPressed knowing what tab is active.
You do the same when the left swipe is detected.
[The stack for each tab is in another array arranged in the order of the tab displayed.
It updates the ViewPager adapter onClick and onBackPressed thus maintaining the navigation history for each tab.]
So:
Effective management of transactions for fragment:
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[Note: In case you are using FragmentStatePagerAdapter, you can play with replacing a fragment with another fragment at a particular index in the list of fragment that you are using as a data for this adapter, in a way that you are in the same tab but its content is changed without changing the tab. Then use notifyDataSetChanged(). Here you do not use transactions, but otherwise you do].
1. Use Fragment.instantiate() to initialize your fragments instead of
constructor.
2. Use listeners to update/delete the reference of instance
(from the collection used to refer them) of fragment onCreateView and onDestroy.
3. Use getView() to get the root view of fragment every where and on update functionality.
4. Do not keep track of instances, in fact avoid static pointers where ever possible.
5. Use getSupportFragment instead of keeping reference of FragmentManager in view pager adapter or elsewhere.
6. Use attach detatch on transaction hide view, to get rid of child views on Fragment's root view and re initialize.
This is because only one fragment needs to be visible at a time, the others need to detach.
Therefore re-attach on demand.
7. getActivity() or getApplicationContext() whatever applicable, instead of keeping a global variable to keep references to context.
8. onConfiguration change (orientation, keyboard, resize): do in activity and pass it to active fragment which manages it.
Important: If you do want to use fragments for transactions, do not declare them in layouts.
Provide container (layout) id in add fragment transaction.
9. A Fragment transaction should be done in an event call, not anywhere else, and such an event should not be repetitive. This prevents Illegal Argument Exception.
10. There is a ViewPager method where you do not have to use Fragments. Instead, you can use Views, or ViewGroups. This replaces the nesting of fragments.
11. Detect the level of fragments, that means if you want a fragment 'B' to replace existing fragment 'A', and when you want to go back to show fragment 'A' when pressing back on 'B', put that transaction in back stack.
BETTER APPROACH:
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Each fragment of tab can have child fragments using child fragment manager, with back stack advantage. Thus you can have navigation history for each tab of the ViewPager.
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Tip : Carefull while adding swipe feature because there are other clickable views.
Swipe with intercept touch on RootView returning false but analysing touches.
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For the Swipe feature handling; properly in your ViewGroups:
Check which events needs to be intercepted and which are to be passed to the child views:
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Swipe gestures on viewgroup
Instead of using my swipe gesture listener in frame-layout on which fragments are attached,
now I am using it on the relative-layouts which are the root-views of the fragments.
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
boolean intercepted = super.onInterceptTouchEvent(event);
// In general, we don't want to intercept touch events. They should be
// handled by the child view.
gestureDetector.onTouchEvent(event);
return false;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
boolean touched = super.onTouchEvent(event);
gestureDetector.onTouchEvent(event);
return touched;
}
Task that remains here is that: intercept the touches in the ViewGroup when the fling is detected, that means return true so that the event is passed to the ViewGroup's onTouch event. This I might achieve by extending the class for the GestureDetector and implement SimpleOnGestureListener.
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One more thing: you should observe that having one fragment in one container at a time resolves another issue: If there are two fragments , one on the top of the other, the clicks from one fragment goes to the other fragment that is beneath. So hide or replace to have just one fragment at a time. Back-Stack helps in maintaining the navigation levels, and on configuration change or update, try to update the same instance of the target active fragment, instead of doing transactions because that changes the order of fragments navigated.
