显示片段时只有 Switch.setChecked 不起作用？

Question

Okey, so first i have an activity

public class MainActivity extends FragmentActivity
{
    private FragmentA a;
    private FragmentB b;
    private FragmentC c;
    private HomeFragment mHomeFragment;


    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.home_activity_layout);
     FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

        getSupportFragmentManager()
                .beginTransaction()
                .replace(R.id.fragment_container, mHomeFragment) // replace flContainer
                .addToBackStack(null)
                .commit();

    ...
    }

i use some lazy initialiser, and i keep my object a, b, c and mHomeFragment inside my activity object,

i have a button inside 'b' that calles the MainActivity to call 'c' and a button inside 'c' that calles the MainActivity to call 'b'

and some other buttons to call 'a' wich is not that important

Well now inside my FragmentB i have some custom views,

  public CustomView(Context cnx, SettingsViewElement e, FragmentA fragment)
    {
    super(cnx);
    inflate(cnx, R.layout.my_layout,this);
    parent = fragment; // i use it later in my onCheckedChangeListener to tell him the the switch has been checked 
    condition = parent.getCondition();

    titleTv = this.findViewById(R.id.title_tv);
    switch  = this.findViewById(R.id.switch);
    if(condition){
    switch.setChecked(true);
    titleTv.setTitle("i am depressed af :(");

    }

my question is :

why my switch doesn't turn checked even if my titleTv is updating the title ??

i did some tests and my OnCreated() is called each time i call replace() in my fragment transaction.

my fragment re-instantiate the views and then will add them to a linearLayout after inflating layout.

Also, if i don't keep my fragments reference in my MainActivity and then re-instantiate it every time. here : the switch.setChecked will work , but the backStack will be huge and dumb

example : stack = 'b' -> 'c' -> 'b' -> 'c' normaly when the user click twice return button he'll be back to homeFragment, he doesn't need to empty the stack by itself.

and even if i override @onBackPressed() and re-instantiate the fragments each time hoping the android sdk will free the space.

i will have to do it manually each time i want to add a new fragment in my design , it will be aa wheel re-invention.

and : IT DOES NOT EXPLAIN WHY THE Switch.setChecked() doesnt work even if the condition is true and the other views are updating (textView is updating it's text)

Update : Apparently,

if the fragment is being re-used and the onCreate() is called for the seconde time, (the reference for the fragment is being kept somewhere and fragment is being attached for a seconde time) here the setChecked will not take an effect, only some other view updates

meanwhile, it will only work if it's being called for the first time the fragment is being created,

Solution : updating the views in the OnResume() methode

If someone has an explanation for this, please go ahead

Answer 1

Views save and restore (some) of there state in the course of saveInstanceState/restoreInstance cycle, but unfortunatrly the checked state (and also visibility etc) are not covered by that. So you'll have implement onSaveInstanceState etc. for your fragment and save/restore the checked state yourself.

EDIT

From your question it is not apparent what view switch actually is so I cannot give you actual code. But have a look at the implementation of CheckedTextView and check out the implementation of onSaveInstanceState() and onRestoreInstanceState() . You'll see that they save and restore the checked state (it's quite a lot of code with the SavedState class but in the end it is pretty simple). What you need to do, is to implement those two methods for your custom view (also creating your own SavedState inner class) and save/restore the checked state of your switch view.

A completely different and better approach would be to use a ViewModel for your fragment that holds the state, but that's a different story that would require lots of changes to your complete implementation.

Answer 2

Update : Apparently,

if the fragment is being re-used and the onCreate() is called for the seconde time, (the reference for the fragment is being kept somewhere and fragment is being attached for a seconde time) here the setChecked will not take an effect, only some other view updates

meanwhile, it will only work if it's being called for the first time the fragment is being created,

Solution : updating the views in the OnResume() methode

If someone has an explanation for this, please go ahead