How to replace fragment in androidx.fragment.app.FragmentContainerView with Android databinding

Question

My current Android application employs databinding.

I having issues when attempting to add a fragment to a androidx.fragment.app.FragmentContainerView .

I have managed to get the effect I was after, however it doesnt feel the correct approach.

I do not understand where I have made a mistake.

in my activity onCreate method I perform this code to set the required fragment

 override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this, R.layout.activity_main)

        if (savedInstanceState == null) manageFragment()
    }

where manageFragment() function resembles this

private fun manageFragment() {
    val myFragment = MyFragment.instance()

    when {
        (currentFragment == null) -> supportFragmentManager
            .beginTransaction()
            .replace(R.id.my_fragment_container, myFragment)
            .commit()

        (currentFragment is MyFragment) -> doNothing()

        else -> supportFragmentManager
            .beginTransaction()
            .replace(R.id.my_fragment_container, myFragment)
            .commit()
    }
}

When I check after manageFragment() this method returns null in onCreate()

supportFragmentManager.findFragmentById(R.id.my_fragment_container)

However when I call the same method in onPostCreate()

override fun onPostCreate(savedInstanceState: Bundle?) {
    super.onPostCreate(savedInstanceState)
    currentFragment = supportFragmentManager.findFragmentById(R.id.my_fragment_container)
}

It has my fragment set

Is this how I should be adding/re[placing fragments when using databinding?

Why doesnt my fragment get returned until postCreate()

Ive a feeling its because once I commit the fragment transaction to add my fragment to the FragmentContainerView , the layout still needs to be measured etc. so "some time" elapses before findFragmentById() can return my added fragment.

is there a layout listener I can add to FragmentContainerView to detect when my fragment is actually added and becomes visible?

Answer 1

Why doesnt my fragment get returned until postCreate()

Commit is asynchronous

is there a layout listener I can add to FragmentContainerView to detect when my fragment is actually added and becomes visible?

Why do you care about this?