Develop Reference

should I use newInstance function somewhere?

I'm new in kotlin and android development.
I was following a tutorial, in that tutorial in a fragment class, companion object, defined a method named newInstance() that returned a fragment, the method was never used.
class myFragment : Fragment(){
companion object {
fun newInstance(foo:Int): myFragment {
val fragment = myFragment()
val args = Bundle()
args.putString("foo", foo)
fragment.arguments = args
return fragment
}
}
}
Is that okay?
Is that going to call it automatically or should I call it somewhere?
(sorry if the explanation isn't good)

It not gonna be used automatically, it is just one of the ways to create fragments.
Basically you need to call this function in the place where you wish to add/ replace this fragment into it's container with the help of FragmentManager

You need to use supportFragment manager in your activity to replace the fragment
val transition = supportFragmentManager.beginTransaction()
transition.addToBackStack("Your_fragment_unique_tag")
transition.replace(containerViewId, fragment).commit()
containerViewId will be FrameLayout id in your activity which is the container for replacing fragment i.e R.id.mainContainer

Get same instance viewModel from nested Fragments

I have a layout which is like that
MainActivity has a NavHost with 3 Fragments
SitesFragment, GroupsFragment, GalleryFragment
GalleryFragment has a ViewPager with 3 Fragments (Image, Audio, Video)
GalleryFragment has a GalleryViewModel
private val galleryViewModel: GalleryViewModel by viewModels()
So inside the ImageFragment i want to get the SAME INSTANCE of GalleryViewModel
private val galleryViewModel: GalleryViewModel by viewModels({ requireParentFragment() })
I tried to get it through the parentFragment but it is not the same instance!
How can i do that?

You can use activityViewModels() rather than viewModels() so your view models are provided by the activity hosting your fragments. https://developer.android.com/kotlin/ktx#fragment

How to get parent Fragment from ViewPager Fragment that is an AndroidEntryPoint?

I have a Fragment within a ViewPager that is created like this:
companion object {
fun newInstance(someData: SomeData): ViewPagerFragment {
val f = ViewPagerFragment()
val args = Bundle()
args.putParcelable("someData", someData)
f.arguments = args
return f
}
}
It is also a Hilt entry point, and it creates its own ViewModel, but also needs the parent Fragments ViewModel, so the top of the class looks like this:
#AndroidEntryPoint
class ViewPagerFragment : Fragment() {
private val parentViewModel: ParentViewModel by viewModels(
ownerProducer = { requireParentFragment() }
)
private val viewPagerViewModel: ViewPagerViewModel by viewModels()
However, the parent Fragment is not found:
java.lang.IllegalStateException: Fragment ViewPagerFragment{b6d6157}
(e5f3fc7d-2ae4-4275-9763-22826a9be939) id=0x7f09017e} is not a child Fragment, it is
directly attached to
dagger.hilt.android.internal.managers.ViewComponentManager$FragmentContextWrapper#1852444
I think this is happening because after adding the viewPagerViewModel the generated ViewPagerFragment class is not a childFragment. Is there a workaround to get the parent Fragment and ultimately get the parent ViewModel? The latter is the main goal.
For now I use ViewPager, not ViewPager2, because it's a legacy infinite wrapper ViewPager.
EDIT:
The ViewPagerAdapter is created like this:
val pagerAdapter = VpPagerAdapter(
requireActivity().supportFragmentManager,
someData,
)

When you create your ViewPager adapter, you need to pass in the childFragmentManager if you want the fragments in the ViewPager to be considered child fragments.

fragment onAttach(context :Context) is not called

I saw many people use fragmentManager for activity to fragment call. So I tried that too. When I click toolbar first, I got the error like this.
kotlin.UninitializedPropertyAccessException: lateinit property mActivity has not been initialized
even though I override and initialize that method, can't see the log when starting onAttach. Why I can't initialize activity? Myfragment is DaggerFragment.
Main button click
binding.toolbar.setOnClickListener {
currentFramgnet = MainPictureFragment().instance
changeFragment(this#MainActivity, binding.fragmentContainer, currentFramgnet!!)
(currentFramgnet as MainPictureFragment).changeDataset("button OnClick")
}
Main changeFragment
fun changeFragment(activity: AppCompatActivity, view: View, fragment: Fragment) {
val fragmentManager = activity.supportFragmentManager
fragmentManager
.beginTransaction()
.replace(view.id, fragment)
.commit()
}
Fragment changeDataset
fun changeDataset(mes : String){
showLog("changeDataset : "+mes)
showToast(mActivity,"11111")
}
Fragment onAttach
private lateinit var mActivity :Activity
override fun onAttach(context: Context) {
super.onAttach(context)
showLog("onAttach")
if (context is Activity) mActivity = context
}
updated : I logged this and found that the changeDataset is called before onAttach()
D/TAG: changeDataset : button OnClick
D/TAG: onAttach

Your problem is you try to access Context before fragment transaction execute because you use commit(). Easy way to fix it is using commitNow().

Fragment Backstack Toolbar title

Is there an efficient way to automatically set the toolbar's title when adding/replacing fragments as well as popping fragments from the backstack?
I have implemented this abstract method in my BaseFragment class:
abstract fun header() : String
override fun onResume() {
super.onResume()
(activity as SSBaseActivity).header.text = header()
}
and I modify the header in each Fragment that inherits from my BaseFragment class and displays the value in onResume but I noticed that when I press back, the last title set isn't being replaced from the fragment currently in the stack.

You could do this by using an OnBackStackChangedListener in your Activity:
supportFragmentManager.addOnBackStackChangedListener {
val fragment = supportFragmentManager.findFragmentById(R.id.yourFragmentFrame)
if (fragment is BaseFragment) {
header.text = fragment.header()
}
}