Android find fragment returns null always - android

I have an activity within it I do
FragmentTransaction trans = getFragmentManager().beginTransaction();
FragmentList fragList = new FragmentList();
trans.replace(R.id.fragList, fragList, "fragList");
to fill my frame layout with the actual fragment. That works fine. Through navigation I end up later in some other activity and some other fragment. In that new fragment I have to call a method of my list fragment to tell it that something has changed.
FragmentList listfrag = (FragmentList) getFragmentManager().findFragmentByTag("fragList");
FragmentList listfrag2 = (FragmentList) getFragmentManager().findFragmentById(R.id.fraglist);
listfrag.updateData(b);
Both, listfrag and listfrag2, are always null. Why?
Edit:
based on the answer that this is not possible from one activity to another activity. I have activity A,
On a tablet A has fragment F1 and F2, on a phone only F1. If I select something on F1, the either F2 gets updated or activity B is called to show F2. In F2 I press a save button and I want to update F1 based. So I either have to call something in the same activity (tablet) or in different acitivty (phone). How can I do this without duplicating my code for the updates?

The getFragmentManager() method gets a reference to the FragmentManager that is used within that activity.
In essence, you are creating the Fragment in one Activity, but looking for it in another. You can't do that (easily).
It sounds like you might want to use startActivityForResult() and onActivityResult() to pass data back and forth between the Activities.

Fragment lifecycle is tied to its activity, you can't call it from another activity. But in the same activity when you replace with another fragment,
Try this,
trans
.replace(R.id.fragList, fragList, "fragList")
.addToBackStack(null) // this will keep fragment when you replace with another.
.commit();

Related

Android. How to avoid fragment be recreated when back from another fragment?

I'm using MVP in my project. I have an activity. Inside this activity I'm showing fragment. Fragment contains some data, edit text, buttons etc. From this fragment it is possible to navigate to another fragment. Here is my code for showing another fragment:
getParentFragmentManager()
.beginTransaction()
.replace(R.id.main_container, secondFragment)
.addToBackStack(null)
.commitAllowingStateLoss();
Next, when I try to go back from fragment 2 to fragment 1, my fragment one is re-created.The method onViewCreated() is called again with saveedInstanceState = null. Also in the onViewCreated() I call presenter.onCreate(savedInstanceState) and because of this, all requests that should be called when I first enter the fragment are re-called when I back to first fragment.
As far as I understand, when calling a .replace(container, fragment), I cannot avoid recreating the fragment view, but in this case, how can I save all my data in the presenter so that I do not re-execute all requests when returning to the fragment?
P.S. With .add() fragment is not recreated. But in my activity I have toolbar with title, and I don't need it to show in my second fragment. When I open my second fragment with .replace() toolbar is not showing, but when open with .add() toolbar is showing.
Use Fragment Result API :
For implemention this method set - setFragmentResultListener - in source fragment and also set - setResult() and finish() - in destination fragment
Note 1 : for having clean code i suggest you to use FragmentTransaction class in:
https://github.com/mahditavakoli1312/FragmentTransaction---mahdi-tavakoli
Note 2 : use Navigation for navigate betwin fragments and activities Instead tranastion

Why after transaction to second fragment landscape mode showing me first transaction again?

I have 2 fragments. My first fragment have button which leads me to second fragment. It has this code:
binding.btnGet5Days.setOnClickListener {
val forecastFragment = ForecastFrag()
val transaction: FragmentTransaction =
parentFragmentManager.beginTransaction()
transaction.replace(R.id.fragment_container, forecastFragment)
transaction.addToBackStack(null)
transaction.commit()
}
In my MainActivity i have this code:
val cityFragment = CityFrag()
val fm: FragmentManager = supportFragmentManager
fm.beginTransaction()
.add(R.id.fragment_container, cityFragment)
.commit()
Fragments are in FragmentContainer,
The problem is when i'm joining second fragment through this button and turn my phone into landscape mode, my first fragment layering to my second fragment. How can i solve it? :)
It's hard to know without seeing your full code, but it's possible the code you posted from MainActivity is adding a fragment on top of the existing stack. When you rotate the device, the Activity is destroyed and recreated, but the FragmentManager maintains its state so you don't lose everything. If your recreated activity code always adds a new fragment instance, you'll end up with what was already there, plus another CityFrag on top
The official recommendation is to use the Jetpack Navigation library, which will handle all that for you. If you don't want to go that far right now, you'll have to do your own checking and creation logic.
One thing you can do is to check if the savedInstanceState Bundle passed into your activity's onCreate is null - if it is, then this is a fresh start, and you can initialise with your first fragment. If it's not null, then your app is being recreated from some saved state, so you should probably let the FragmentManager take care of restoring itself and its back stack.
Otherwise take a look at FragmentManager - there's a bunch of useful methods like getBackStackEntryCount, findFragmentByTag etc. that you can use to work out what state your fragments are in, and if you need to add one or not. Depends on your code!

How to handle fragment backstack

I'm having problem with fragment. Lets try to understand my issue, I have two fragment A and B. When app start with main activity,i start fragment A as you can see :
getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new MusicFragment())
.commit();
When i click on a button, it starts fragment B
getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new BarFragment())
.addToBackStack(null)
.commit();
Main problem is after starting fragment B,when i pressed back to go back to fragment A , Fragment A Recreated with new state.
I don' want to recreate fragment A. I only want to start fragment from old state where i left. How to fix it ?
Instead of calling the replace method you should be calling the add method with a subsequent call to addToBackStack with an argument of null. The add method adds the fragement to the stack with a null tag and calling the addToBackStack with an argument of null then the current fragment is stopped upon commit. If the method is not called then the current fragment is destroyed and recreated when coming back.
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container,new BarFragment())
.addToBackStack(null)
.commit();
You can clearly find it in the documentation quote saying this:
If you don't call addToBackStack() when you perform a transaction that
removes a fragment, then that fragment is destroyed when the
transaction is committed and the user cannot navigate back to it.
Whereas, if you do call addToBackStack() when removing a fragment,
then the fragment is stopped and is later resumed if the user
navigates back.
Here are some points that need to be taken care while creating fragments.
Check the backstack if the fragment is already created.
If it was created previously pop it from the backstack and put it on top so that it is visible to the user.
If fragment is not present in backstack crate it and store it in backstack.
Create a method like below which will handle such situation.
private void openFragment(Fragment fragment_to_be_opened){
String fragment_to_be_opened_name = fragment_to_be_opened.getClass().getName();
FragmentManager manager = getSupportFragmentManager();
// fetching the fragment if it is present in backstack
boolean fragment_allready_present = manager.popBackStackImmediate (fragment_to_be_opened_name, 0);
if (!fragment_allready_present){ //fragment is not present in backstack so create it and save the name in //backstack
FragmentTransaction fragment_trasition = manager.beginTransaction();
fragment_trasition.replace(R.id.fragment_container, fragment_to_be_opened);
fragment_trasition.addToBackStack(fragment_to_be_opened_name);
fragment_trasition.commit();
}
}
Now call this method from the activity to open a new fragment like
// create instance of fragment and pass it to the open fragment method
Fragment myFragment = new myFragment();
openFragment(myFragment);

Android: How to start a new fragment without destroying the state of the previous fragment?

How to replace Fragment_1 Fragment_2 with the ability to return back to the state and Fragment_1 (scroll, inputs, forms, other)?
enter image description here
If you use Activities, then you can use the method startActivityForResult. The work of this method perfectly shows the current task with fragments.
I do not want to save the values and then substitute them. We need that to Fragment_1 remained intact.
How to save the status of previous fragments at the opening of the new fragment_N and when you turn the screen using backstack?
Is there a ready library for the implementation of these tasks?
Instead of replacing fragment, You can add a new fragment and hide current one.
Something like this
FragmentTransaction t = getFragmentManager.beginTransaction();
t.hide(your_current_fragment);
t.add(container, new_fragment);
t.addToBackStack(TAG);
t.commit();
It will not loss the state of hidden fragment
FragmentTransaction t = getFragmentManager.beginTransaction();
t.hide(your_current_fragment);
t.add(container, new_fragment);
t.addToBackStack(TAG);
t.setCustomAnimations(R.anim.open_enter,R.anim.close_exit,R.anim.open_enter,R.anim.close_exit)
or
t.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
t.setTrans
t.commit();
replace FragmentPagerAdapter with a HorizontalScrollView contains 2FrameLayout for fragment.You can freely change fragment in FrameLayout.

"Can't change container ID of fragment" when using "replace"

So I've found a few similar cases, but nothing about this specific case.
I have a FrameLayout which I gave the id "container", and contains a few different fragments.
In my code for the activity that contains that FrameLayout, I'm trying to switch between the fragments with a function that receives a fragment.
In that code:
a. I have defined private FragmentManager fm = getSupportFragmentManager();
b. I have defined FragmentTransaction ft; to use later.
c. My function is:
private void setActiveFragment(Fragment fragment){
//Determine which button should be marked as "active"
determineButtonByFragment(fragment);
//Repalce fragment
ft = fm.beginTransaction();
ft.replace(R.id.container, fragment);
ft.addToBackStack(String.valueOf(fragment.getId()));
ft.commit();
}
Any idea why i would get this error on the "replace"?
EDIT:
Ok, I just realized a bit more about fragments. Since all 5 fragments are added to the FrameLayout, the "replace" won't work. You get the "can't chance container ID error" when you're trying to move a fragment from 1 parent view to another (Or in this, case, to the same one), without detaching it first.
Let's say I have fragments A, B, C, D, E.
If I want to replace to fragment B right now, I won't be able to do it until I remove it from it's original parent (Or at least that's how I think it works. please enlighten me otherwise). The only question that remains now, is how do I switch between my fragments correctly...
Alright, apparently you cannot use the "replace" method on fragments which are hard-coded in the layout:
Replacing a fragment with another fragment inside activity group
What I have to do now, is inside the function, to find a way to determine the fragment I want to display, create a new instance of it, and use "replace" on it.

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