I've implemented navigation in my Android app as one Activity and many Fragments.
When I open new child Fragment, I call this:
FragmentTransaction tx = getSupportFragmentManager().beginTransaction() .addToBackStack(null).replace(R.id.fragment_container, f)
.setBreadCrumbTitle(f.getClass().getSimpleName());
tx.commit()
This works quite well, as old fragment isn't destroyed, so when I go back in the back stack, the old fragment retains the scroll position and everything entered on it.
The problem is, in one Fragment I actually need to pause something when I add another fragment above it. I've thought that onPause() will be called, but it doesn't - I suppose that all other fragments live beneath the ones on top of them.
On the side note, I also think that my app gradually slows down as the user navigates deeper. Shouldn't I be replacing the fragment in the transaction instead, so only one is on the top?
Related
I have a Navigation panel activity. With 5 fragments (Will name it as Fragment1, Fragment2, ...) in menu sections.
Now by Default, activity will display Fragment1.
If user navigate to Fragmentxtz from Fragment1. We will add the fragment on top of Fragment1.
Now user goes to background by pressing home button and open the app from tasks.
Now i know Fragmentxtz onStart will be called. But i see that Fragment1 onStart is also called.
Is this expected behavior ?
As you can see on Android Developers, your fragment will be called at onViewCreated().
https://developer.android.com/guide/components/fragments#Creating
The View has to be updated in case you changed the system language or something like that.
Providing a bit more context to what might be happening here.
If both of your fragments are added e.g. via FragmentTransaction.add() both of them will have onCreateView() called when the layout is restored for the user as Robert pointed out. From the system's point of view all of those fragments are relevant to the user and would be shown simultaneously.
If on the other hand you add fragments via FragmentTransaction.replace() only the topmost fragment on the back stack will receive the onCreateView() call. This can also be achieved by doing an add and remove of the old fragment. If you make this transaction reversible by the back stack after pressing the back button your previous fragment would receive the appropriate lifecycle callbacks.
I have the following problem:
I have three fragments that I can switch through swiping. The first contains images that are regularly made visible and invisible by an external method. However, I see the change in the visibility of the images only when I leave the fragment by swiping and then swipe back again.
Therefore, the question is which method is called when rewinding back, so that I can call this explicitly if the fragment is visible.
I think this will help when you back on the fragment.
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.detach(this).attach(this).commit();
Scenario:
I have a fragment which has a ViewPager which contains 5 instances(different) of a single Fragment with different values, each having a listivew that contains some sort of items.
Problem:
The flow goes smooth when I click an item of listView(say on page1) but the moment I come back from there on pressing back (overridden OnBackPressed in the main_activity (will discuss later)), the viewPager fails to load the subFragments.
But when I switch to the 2nd or 3rd page, it gets displayed, and on going back to 1st page, it now gets displayed.
OnBackPressed():
I am maintaining a manual stack here. When I click on an item of ListView, the current Fragment Instance (of the parent Fragment ofcourse) goes into stack. And when user comes back , that instance gets popped off the stack and I replaces it on the activities FrameLayout container.
References:
Fragments not getting recreated by FragmentStatePagerAdapter after coming back to the main Fragment instance
Guys, I am really pissed off here, please help me out.
Frankly, I haven't worked much with fragments.
But it seems like the page is being thrown off the memory every time you switch to other pages. I am not sure but if there is a way for android to manage this and keep the page in its memory persistently, it might solve the problem
Finally I am able to get a workaround for this issue, which included two things:
while replacing the fragment make a call to
ft.replace(R.id.content_frame, frag).addToBackStack(null);
while initiating the ViewPager, the fragment manager to be used is :
mAdapter = new myAdapter(getChildFragmentManager());
Actually the problem is that, android fails to recognise and load the older instance of the fragment unless you explicitly add that instance to the backstack. So after adding it to BackStack, there is practically no need to maintain your own manual Stack, but you still can do that.
I have looked around and found variations of this question, but all of the answers seem to be ugly hacks. Is there no easy and proper way to achieve this?
Say for instance I have Activity A, which has a FrameLayout that can hold one fragment at a time. Lets say that when the Activity is first started it loads Fragment A into the FrameLayout, which consists of a ListView. When an item is selected in Fragment A it starts up Fragment B. The way I am currently doing this is by simply hiding Fragment A and then adding Fragment B since this preserves Fragment A's state. I am of course also adding this fragment transaction to the backstack.
So now Fragment A exists on the backstack. Say now I go back to my Android home screen and go to another app. While I am doing this, the Android system decides to destroy my application because the system needs more memory. When I navigate back to my application, how am I supposed to properly restore the state of Fragment B, and Fragment A which is currently on the backstack.
I cannot use setRetainInstance() since it does not work for Fragments placed on the backstack.
Essentially what I am trying to do is restore the backstack to exactly how it was before my application was forcefully closed. So Fragment A should be on the backstack (but not showing), and Fragment B should be currently showing. If I hit the back button, it should properly pop Fragment A off the backstack.
Some notes
Since the application was forcefully closed, it's savedInstanceState != null. Same thing holds for the fragments.
I'm trying to add animation to my android app, and knew a lot about transition animation between activities, and about fragments. So I have MainActivity with some view (image), and SecondActivity which is empty itself, but contains fragments, which then needs to be used to display some detail information about this image. I've read about postponeentertransition() and it worked. But the problem is, that this fragment in second activity have links(or transitions) to the same kind of fragment.
Let's say in main activity I have set of images of cars, then I click one, second activity is starting and waiting for fragment loading, and then shows animation. And then, in this fragment I have "similar cars" recycler, and choose one of them, and wants, to show its details the same way, but with adding this fragment to the backstack (not replacing). So the problem is that transition name of the view in main activity and big image of fragment are the same (which is obvious), and transition name in fragment's recycler and big image of the next fragment have to be the same too(otherwise app doesn't know how to make the animation). On the other side, fragment (which was added) has to be the same class, but its different instance.
I just want to set up animation without crashing the existing architecture.:) If you have any solutions or advices how to make animation between different instances of one fragment, please help.)
Use setCustomAnimations on the Fragment transaction (see below). It doesn't matter if the instances are from the same class.
FragmentTransaction transaction = mActivity.getSupportFragmentManager().beginTransaction();
// To animate the fragment
// NOTE: Must be before replace/add otherwise it doesn't work
transaction
.setCustomAnimations(enter, exit, popEnter, popExit)
.replace(R.id.frame_container, fragment, null)
.commit();