Fragment management

Add dependency to use fragments

val fragment_version = "1.3.4"

// Java language implementation
implementation("androidx.fragment:fragment:$fragment_version")
// Kotlin
implementation("androidx.fragment:fragment-ktx:$fragment_version")

FragmentActivity is a base class for activities that want to use fragments. For example, AppCompatActivity class is direct subclass.

Activity can have list of fragments. Also each fragment can have its own list for child fragments.

FragmentManager class is responsible for performing actions on your app's fragments, such as adding, removing, or replacing them, and adding them to the backstack. You can get it with the getSupportFragmentManager() method of FragmentActivity.

Inside a fragment, you can get a reference to the FragmentManager that manages the child fragments with getChildFragmentManager() method. If you need to access its host FragmentManager, you can use getParentFragmentManager() method.

FragmentTransaction represents an operation on to a list of fragments. You can save transaction in the fragment backstack.

A FragmentManager.BackStackEntry interface represent an entry of the fragment backstack, as created with FragmentTransaction.addToBackStack(). Entries can later be retrieved with FragmentManager.getBackStackEntryAt().

You should never hold on to a BackStackEntry object; the identifier as returned by getId() is the only thing that will be persisted across activity instances.

FragmentManager

class ExampleActivity : AppCompatActivity(R.layout.example_activity) {
 
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // set our fragment as root fragment at first time  
        if (savedInstanceState == null) {

            val bundle = bundleOf("some_int" to 0)
            
            supportFragmentManager.commit {
                setReorderingAllowed(true) // You should always use it in transaction
                add<ExampleFragment>(R.id.fragment_container_view, args = bundle)
            }
        }
    }
}

FragmentTransaction

fragmentManager.beginTransaction()
    .setCustomAnimations(enter1, exit1)
    .add(MyFragmentClass, args, tag1) // this fragment gets the first animations
    .setCustomAnimations(enter2, exit2)
    .add(MyFragmentClass, args, tag2) // this fragment gets the second animations
    .commit()