Develop Reference

Change order of fragments

I am using FragmentManager to dynamically add fragments to an activity. How can I add a new fragment before another one instead of just at the end without having to redo the entire set of fragments?
For example, on the activity there are three fragments shown vertically like this:
FragA
FragB
FragC
When I add a fourth fragment NewFragD they should now be arranged like this:
FragA
NewFragD
FragB
FragC

You need something like this:
#Override
public Fragment getItem(int position) {
if (position == 0) return new frg1();
else if (position == 1) if (newFragment)return new Mapfrag2(); else return frg2()
else if (position == 2) return new frg3();
else return new frg1();
}

I have had a similar issue and I don't think it's possible to reorder fragments already committed.
The way I fixed this issue that I found to be better than clearing and re-adding the fragments in the right order is to have all the potential fragments added in the correct order and then show/hide when they are ready to be displayed.
So in your example, you would initially have:
transaction.add(FragA)
transaction.add(FragD)
transaction.add(FragB)
transaction.add(FragC)
and then this line before committing the transaction
transaction.hide(FragD)
and when it's time to show the frag you would create another transaction and add this line
transaction.show(FragD)
This is better since all the fragments wouldn't have to go through the lifecycle again. I've found that using show/hide instead of trying to add a fragment to the transaction results in clearer and more performant code.
This will only work if you have a fixed order for all potential fragments, if you need to dynamically change the order then you would resort to clearing and adding fragments in the proper order each time you need to update it.

Android BackStack NavigationDrawer

I have a problem that I've been dealing with for the last couple o days and don't seem to find an answer to it.
Description : I have a main activity which contains a navigation drawer. Each item of the navigation drawer (when clicked) creates a fragment. In that fragment, there is a listView of objects, which creates other fragments when clicked. In those fragments i have another listView of objects which opens other fragments. In other words, there series of fragment that open other fragment. Something like this:
http://s22.postimg.org/pddo5gsv5/backstack.png
In order to be able to get back to each fragment, I've implemented the addToBackstack("string") method.
My question is, how can I implement correct backstack for my application so that when i click a navigation Drawer item, all the fragments that have been added to backstack are cleared, without the one that the navigation Drawer item opens.
Any help would be appreciated. Thank you !
EDIT
Ok, it seems I managed to figure it out. Considering what advices i received from the replies, here's the solution I came up with:
#Override
public void onBackPressed() {
int count = getFragmentManager().getBackStackEntryCount();
if (count != 0) {
FragmentManager.BackStackEntry backEntry = getFragmentManager()
.getBackStackEntryAt(
getFragmentManager().getBackStackEntryCount() - 1);
if (backEntry.getName() == NAVIGATION) {
finish();
} else
getFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
}
To put it in words: First, i added a backstack entry even for the top level fragments, given them a specific tag. The I have overridden the Activity's back button function so that when the last backstack entry is a top-level fragment to finish the activity (so that it not simply detach the fragment from activity, living it empty). Otherwise, if the last entry isn't an top-level fragment, execute a popBackStack.
PS: All non-top-level fragments are added to the backstack with a different tag then the top-level one. Also, i had to do a POP_BACK_STACK_INCLUSIVE in the navigation Drawer's click listener.
getFragmentManager().popBackStack(null,
FragmentManager.POP_BACK_STACK_INCLUSIVE);
Thank you all for the advices and hopefully this EDIT help other users.

You can use the following code to solve your problem:
getFragmentManager().beginTransaction()
.replace(R.id.fragment_container, fragment)
.addToBackStack(fragment_tag)
.commit();
In order to make the code above work, you have to create the fragments dynamically. As hardcoded fragments cannot be replaced. To do that, you can create a container (FrameLayout etc.) which in our example has the id fragment_container. Then, the code above will add the fragment in the container dynamically. Finally, you have to pass as parameter in the addToBackStack method the fragment_tag. That means, that this transaction will be added in the back stack. And finally, in order to get it from the backstack you have to use the code below:
getFragmentManager().popBackStack(fragment_tag, FragmentManager.POP_BACK_STACK_INCLUSIVE));
The POP_BACK_STACK_INCLUSIVE flag, insures that "all matching entries will be consumed until one that doesn't match is found or the bottom of the stack is reached. Otherwise, all entries up to but not including that entry will be removed."

You can clear the fragment backstack by using something like:
fragmentManager.popBackStack("string", FragmentManager.POP_BACK_STACK_INCLUSIVE);
and then you can addToBackstack and commit as usual. More info.
A code snippet that shows the way I normally use it in navigation drawers:
FragmentManager fragmentManager = getSupportFragmentManager();
if(clearBackStack) {
fragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
}
FragmentTransaction ft = fragmentManager.beginTransaction();
ft.replace(R.id.content_frame, fragment);
if(!clearBackStack) {
ft.addToBackStack(null);
}
ft.commit();

Android fragments wont show

i have a piece of code where i wish to just hide the current fragment so it doesnt destroy its view and then show a new one using this :
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.hide(oldFragment);
ft.show(newFragment);
ft.commit();
The issue is that when i execute the above code, it doesnt show any UI components.
if i do ft.replace(id,fragment); it works but i do not want to remove the previous displayed fragment as i want to maintain the fragments and its views so i dont need to re-initialise it

Did you previously add newFragment to some part of your Activity's view hierarchy? If you just instantiate a Fragment and tell it to show, it won't know where to show (unless it's a DialogFragment, I guess). You need to use add(somelayoutid,fragment,"sometag") for each Fragment and then you can hide/show them as you'd like. You can also just continually use replace, rather than hide/show, if you don't need to keep your Fragment's around while they're hidden.
"sometag" will be useful if you're handling rotation so you can retrieve a reference to each Fragment after your Activity is recreated, and then you can hide/show them as before.

Was your fragment initialized before calling this?
if (newFragment == null) {
// If not, instantiate and add it to the activity
ft.add(yourFragmentContainerId, newFragment,"tag");
} else {
// If it exists, simply attach it in order to show it
ft.show(newFragment);
}

How to keep only first added Fragment in back stack (fragment overlapping)?

Scenario what i'm trying to achieve:
Loading activity with two frame containers (for list of items and for details).
At the app launch time add listFragment in listFrame and some initial infoFragment in detailsFrame containers.
Navigating through list items without adding each detail transaction to back stack (want to keep only infoFragment in stack).
As soon as user hit back button (navigate back) he falls back to intial infoFragment what was added in launch time.
If sequential back navigation fallows then apps exit.
My code:
protected override void OnCreate(Bundle savedInstanceState)
{
...
var listFrag = new ListFragment();
var infoFrag = new InfoFragment();
var trans = FragmentManager.BeginTransaction();
trans.Add(Resource.Id.listFrame, listFrag);
trans.Add(Resource.Id.detailsFrame, infoFrag);
trans.Commit();
...
}
public void OnItemSelected(int id)
{
var detailsFrag = DetailFragment.NewInstance(id);
var trans = FragmentManager.BeginTransaction();
trans.Replace(Resource.Id.detailsFrame, detailsFrag);
if (FragmentManager.BackStackEntryCount == 0)
{
trans.AddToBackStack(null);
}
trans.Commit();
}
My problem:
After back button has been hit, infoFrag is overlapped with previous detailFrag! Why?

You can do this:
if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
getSupportFragmentManager().popBackStack(getSupportFragmentManager().getBackStackEntryAt(0).getId(), getSupportFragmentManager().POP_BACK_STACK_INCLUSIVE);
} else {
super.onBackPressed();}
In your activity, so you to keep first fragment.
You shouldn't have, in your first fragment, the addToBackStack. But, in the rest, yes.

Very nice explanation by Budius. I read his advice and implemented similar navigation, which I would like to share with others.
Instead of replacing fragments like this:
Transaction.remove(detail1).add(detail2)
Transaction.remove(detail2).add(detail3)
Transaction.remove(detail3).add(detail4)
I added a fragment container layout in the activity layout file. It can be either LinearLayout, RelativeLayot or FrameLayout etc.. So in the activity on create I had this:
transaction.replace(R.id.HomeInputFragment, mainHomeFragment).commit();
mainHomeFragment is the fragment I want to get back to when pressing the back button, like infoFrag. Then, before EVERY NEXT transaction I put:
fragmentManager.popBackStackImmediate();
transaction.replace(R.id.HomeInputFragment, frag2).addToBackStack(null).commit();
or
fragmentManager.popBackStackImmediate();
transaction.replace(R.id.HomeInputFragment, frag3).addToBackStack(null).commit();
That way you don't have to keep track of which fragment is currenty showing.

The problem is that the transaction that you're backing from have two steps:
remove infoFrag
add detailsFrag (that is the first1 detail container that was added)
(we know that because the documentation This is essentially the same as calling remove(Fragment) for all currently added fragments that were added with the same containerViewId and then add(int, Fragment, String) with the same arguments given here. )
So whenever the system is reverting that one transaction is reverting exactly those 2 steps, and it say nothing about the last detailFrag that was added to it, so it doesn't do anything with it.
There're two possible work arounds I can think on your case:
Keep a reference on your activity to the last detailsFrag used and use the BackStackChange listener to whenever the value change from 1 to 0 (you'll have to keep track of previous values) you also remove that one remaining fragment
on every click listener you'll have to popBackStackImmediatly() (to remove the previous transaction) and addToBackStack() on all transactions. On this workaround you can also use some setCustomAnimation magic to make sure it all looks nice on the screen (e.g. use a alpha animation from 0 to 0 duration 1 to avoid previous fragment appearing and disappearing again.
ps. I agree that the fragment manager/transaction should be a bit more clever to the way it handles back stack on .replace() actions, but that's the way it does it.
edit:
what is happening is like this (I'm adding numbers to the details to make it more clear).
Remember that .replace() = .remove().add()
Transaction.remove(info).add(detail1).addToBackStack(null) // 1st time
Transaction.remove(detail1).add(detail2) // 2nd time
Transaction.remove(detail2).add(detail3) // 3rd time
Transaction.remove(detail3).add(detail4) // 4th time
so now we have detail4 on the layout:
< Press back button >
System pops the back stack and find the following back entry to be reversed
remove(info).add(detail1);
so the system makes that transaction backward.
tries to remove detail1 (is not there, so it ignores)
re-add(info) // OVERLAP !!!
so the problem is that the system doesn't realise that there's a detail4 and that the transaction was .replace() that it was supposed to replace whatever is in there.

You could just override onBackPressed and commit a transaction to the initial fragment.

I'm guessing but:
You've added the transaction to replace infoFrag with 1st detailsFrag into the backstack.
But then you replace 1st detailsFrag with 2nd detailsFrag.
At this point when you click back, the fragment manager cannot cleanly replace 1st detailsFrag with infoFrag as 1st detailsFrag has already been removed and replaced.
Whether the overlapping behaviour is expected or not I don't know.
I would suggest debugging the Android core code to see what it is doing.
I'm not sure whether you can achieve without say overriding Activity::onBackPressed() and doing the pops yourself having added all transactions to the backstack.

Swap two fragment simultaneously

In my application i have one activity and i am adding two fragments at run time.I need to swap these two fragment simultaneously. Fragment 1 consist a button and i want when i click that button fragment 1 moves to right side of the screen and other fragment to the left side of the activity.
In the onClick method of the button i tried something like this
#Override
public void onClick(View v) {
FragmentTransaction ft = getFragmentManager().beginTransaction();
Fragment newFragment = getFragmentManager().findFragmentById(R.id.pageA);
ft.remove(newFragment);
Fragment newFragmentB = getFragmentManager().findFragmentById(R.id.pageB);
ft.remove(newFragmentB);
ft.add(R.id.pageB, newFragment);
ft.add(R.id.pageA, newFragmentB);
ft.addToBackStack(null);
ft.commit();
}
But i am getting the following error
java.lang.IllegalStateException: Can't change container ID of fragment PageA{40653da0 #0 id=0x7f060001}: was 2131099649 now 2131099650
I want something like this when i click the button on Page A then Position of Page A and PageB should swap with each other.

I have a similar issue ( IllegalStateException: Can't change container ID of Fragment ) and i solved by swapping the containers instead of the fragments... Nonetheless i still have no clue as to whether it's possibile to swap directly fragments. As I wrote in the aforementioned post, it seems to work only on ics!

I posted a solution to this problem to a similar question. My approach is to re-create the fragment, but keeping the state by saving it first and re-applying it to the new instance.
See https://stackoverflow.com/a/14951987/599614.