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how ViewPager2 handle fragments

In my app I have a ViewPager2, the fragment inside this ViewPager have some code on onViewCreated. I have 2 question:
If I update the dataset and then return to old one the onViewCreated is not called, because of fragment cache, how can I intercept the re-show? I am ok with cache, bui I want restore the initial focus of the fragment when re-showed.
How can I intercept the hiding from the fragment? My fragment show a dialog, then an external event can change the data set, I want in this case dismiss the dialog.
Are 2 days that I am trying to fix those 2 issues.
EDIT: I solved the 2 observing the changing of data set.

Data sharing by ViewModel looks like a good solution for both cases. Fragments will rely on data change in shared ViewModel (depends on the structure of your screen it can be data sharing with host activity or parent fragment).
If it's not what you are looking for, provide more details.

Updating edittext from fragment

I currently have the following situation:
1) The "main view" which contains the EditText I'm trying to update. (Let's call it mainView)
2) A fragment that is opened whenever I click in a button that is contained in the "main view", the
fragment receives mainView as parameter.
3) An OnClickListener which is set to a button that is contained by the fragment. This listener receives the fragment as parameter.
Basically what I need to do is, each time I click on the button that triggers the listener, I need to update the editText, however it doesn't seem to be working. I believe it has something to do with "notifying" the view, but I haven't been able to get it working no matter what I try. After I update the text I close the fragment and
Basically the code is the following:
public void onClick(View v){
String newMessageContent = "hello world";
fragment1.mainView.editText1.setText(newMessageContent);
FragmentManager manager = this.fragment1.getActivity().getFragmentManager();
manager.beginTransaction().replace(R.id.container,this.fragment1.mainView.getPlaceHolderFragment()).commit();
}
Please note that I have simplified the problem a little bit and changed the name of the fragment/views in order for you guys to understand better. The text "hello world" is actually dynamic, and depends no another parameter that is received by the OnClickListener.
After I click the fragment does get replaced, so I know the onClickListener is working correctly, however I believe there's something wrong with the way the data change is being notified.
I've already looked at many SO questions, however none of them have helped me to achieve what I need.
Any help is appreciated, thanks.

I suggest implementing an interface, say, IUpdateFromFragment with method, say, onUpdate(String message), then let activity implement that interface and inside the fragment just call something like ((IUpdateFromFragment)this.getActivity()).onUpdate(newMessageContent);

I realized the problem was that each time I replaced the fargment via the fragmentManager, the method setActivityView was being called again, which replaced the EditText content.
In order to avoid this, I manually removed the fragment (instead of replacing it), doing the following:
FragmentManager manager = this.selectTemplateFragment.getActivity().getFragmentManager();
manager.beginTransaction().remove(this.selectTemplateFragment).commit();

Update the fragment via transaction, then within the fragment1 class OnViewCreated, you can do mainView.editText1.setText("whatever");
The way you're doing this now, I'm surprised isn't throwing an exception since the view isn't inflated yet.

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

Getting fragment instance in my activity

Is there some way I get already created currently displayed same instance of fragment in my activity. I DON'T to use
findFragmentById(int id), simply I never created that
findFragmentByTag(String tag), because I am not adding tag in every fragment .offcourse due to some requirement.
getFragment(Bundle bundle, String key), because I never am putting in bundle.
Although I may look like fool to mention that, but I want something like this. Is activity keep some fragment instance somewhere.??
What can be the best approach I can take to achieve this requirement.
UPDATE
Okay, so let me tell you why I can't use above methods. If I am adding various fragment in one activity, where I always want to come back to one fragment when back is clicked. (As we have in navigation drawer, u know). And unless there are inner fragment. so for that I don't want to add in the back stack.
Now even if I have the tag associated with my fragments, I cant say for 8 fragment if- else-if-else for getting the tag. That I know is not correct. So first two ways goes out of my option. Now third one. I exactly don't know where to keep it. And even if I keep it where will I get the bundle and key every time I just want my fragment.

You can get from fragment Manager
List<Fragment> fragList=fManager.getFragments();
for(Fragment fr: fragList){
String fragClassName = fr.getClass().getName();
if(fragClassName.equals(Abc.class.getName())){
Log.i("Fragment:","Abc");
}else if (fragClassName.equals(Xyz.class.getName())) {
Log.i("Fragment:","Xyz");
}
}

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().