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How to make button open another fragment from within another fragment in kotlin

how to make button to open another fragment. being within a fragment. kotlin
I'm starting in kotlin and I'm having a hard time trying to open a fragment with a button, how do I?

You need to use FragmentManager and FragmentTransaction to add your fragment on the fly. you can call a function similar to this in your button's onClick method. But it is recommended for the parent activity to handle each fragment's lifecycle and the fragments
are not supposed to interact each other. The following is taken from the developer docs, that can be found here.
"Often you will want one Fragment to communicate with another, for example to change the content based on a user event. All Fragment-to-Fragment communication is done either through a shared ViewModel or through the associated Activity. Two Fragments should never communicate directly."
fun createFragmentonTheFly(){
var mFragmentTransaction: FragmentTransaction = getSupportFragmentManager().beginTransaction()
mFragmentTransaction.add(R.id.fr_container,new ProductListFragment())
mFragmentTransaction.commit()
}
The best way to do it would be to add an interface let say onFragmentDetachedLisetner and add one method replaceFragment() or something and make your Activity implement this interaface and had it replace as soon as the fragment is detached and make your fragment that contains your button finish itself when user clicks the button, then your activity will replace it with the one you wanted to start. And also consider reusing fragments, as that is the main purpose of fragments at the first place.

how to save my fragment content? how to refresh my fragment?

I have 2 fragments which are called from the action bar of an activity. Both are gridviews, the first one displays applications with a dedicated adapter, and the second one displays a file list with another adapter. My problem is that when I launch a file then when I back to my activity I switch from one fragment to another, when I come back to the previous one, its content disappears. And when I rotate tablet I have the some problem, because my Fragment restart so for this I think that removing fragment give the possibility to create a new Fragment up to date. How can I save and reload data in my fragment.
How can I manage to update the content of the first fragment while coming back from the second one ? And how to remove fragment after the rotation in order to recreate the Action with new Fragment? I asked this questions but I don't have any responses. the code is given below

If your data is just strings or integers, you can make use of shared preferences to store and retrieve data.

Solution to your first problem -how to save fragment state
Use setRetainInstance(true) in you fragments onCreate() *it prevents your fragment from destroying and hence recreating.
Add your fragment to back stack
declare your adapter globally in fragment and resuse it when you get back.
when, you get back to fragment its onCreateView() method will be called directly. hence initialize your adapter in onCreate() method and use it in onCreateView().
Solution to your second problem -how to update fragment content
For this you can use interface. create interface in your second fragment and implement it in your first fragment. prefer this doc for this,
http://www.vogella.com/tutorials/AndroidFragments/article.html#fragments_activitycommunication

How to prevent calling onCreateView when back button pressed in fragment in android

In my application, I have tabbar functionality. In one tab i am displaying server data in lisview, and on clicking on that detail page for that list item will be open in new fragment.
But when I press back button from that detail page, every time oncreateview called of previous page, so every time listview created and new fetches new server data. So how to prevent such and just display previous state when back button press?

I know it has been too long to give this answer but what i am guessing is you are replacing your fragment with other one. I mean to say is you are using
ft.replace(R.id.realTabContent, fragment);
to move to other fragment which is you are using in your onItemClick so simple solution is use
ft.add(R.id.realTabContent, fragment);
instead of replacing your fragment.
Understand the difference between replace and add. This will solve your problem.
Replace : it will replace the original fragment and re-create the view when you come back
Add : it will just add a new fragment to stack.
Hope this will help someone who is facing the same problem...

I don't think prevent calling onCreateView is a good idea, beside if the function is not called, there will be exception, so NO, you shouldn't. Instead of doing that, I suggest you move your "listview created and new fetches new server data" into another place where you can call explicitly (when you want, where you want, onCreate() is a good place), don't put it in onCreateView(). Hope this helps.

You should cache your data objects apart from view variables as their references needs to be updated if you are fetching any data from server and don't want to make a call again then use branching to branch out that code.
Create an init() method where you do all initialization and server calls and logically branch out call to init() method whenever you don't want to call init().

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.

Android fragment instances avoid duplicates

Hi I am not sure I am doing the right thing. I have several fragments in one activity (not shown at the same time). When I add the fragment do I have to check if a previous instance exists? I am using the compatibility package and my fragment CameraFragment is a separate class (in its own file):
private void addNewFragment(Fragment fragment, String tag) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.frag1, fragment, tag);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
ft.addToBackStack(null);
ft.commit();
}
and then :
public void startPicTaking() {
addNewFragment(CameraFragment.newInstance(), TAG_PIC_TAKING);
}
So each time a user clicks a button to take a picture I use this methods BUT shall I verify if the fragment already exists and remove it first or does the static method newInstance make sure the fragment is not duplicated?
I have read the doc several times but I don't understand why the line:
ft.addToBackStack(null);
what is it for? I know you can pop the back stack and it keeps the transaction but how can it be used and for what? Is it necessary or if I don't use it I can skip it?
thanks

I have several fragments in one activity (not shown at the same time). When I add the fragment do I have to check if a previous instance exists?
No, it will just create a new instance of that Fragment when it adds the next instance of it. It will not affect the previous instance of it.
So each time a user clicks a button to take a picture I use this methods BUT shall I verify if the fragment already exists and remove it first or does the static method newInstance make sure the fragment is not duplicated?
You could do that if you wanted to, to ensure that no Fragment appears twice in the stack. (So when you hit back, you don't get the same activity again.) Depending on exactly what appears in your back stack, you may not want to remove stuff lower down. (Consider that a user expects previous fragments to appear when he hits the back button.)
I have read the doc several times but I don't understand why the line: ft.addToBackStack(null); what is it for?
When Fragment objects are added to the back stack, then each time the user hits back, they will go to the previous item on the stack. If you do not add an item to the back stack, the user will not encounter it when they hit the back button.