Android 4.2: back stack behaviour with nested fragments

Question

With Android 4.2, the support library got support for nested fragments see here. I\'ve played around with it and found an interesting behaviour / bug regarding back stack an

Answer 1

After observing some solutions presented here, I found that to allow flexibility & control for the parent fragment as to when popping the stack or when the back action should be ignored by it, I rather use such implementation:

Defining a "ParentFragment" interface:

interface ParentFragment {
/**
 * Fragments that host child fragments and want to control their BackStack behaviour when the back button is pressed should implement this
 *
 * @return true if back press was handled, false otherwise
 */
fun onBackPressed(): Boolean

}

Overriding the "onBackPressed" in the parent activity (or in the BaseActivity):

override fun onBackPressed() {
    val fm: FragmentManager = supportFragmentManager
    for (frag in fm.fragments) {
        if (frag.isVisible && frag is ParentFragment && frag.onBackPressed()) {
            return
        }
    }
    super.onBackPressed()
}

And then allow the parent fragment to handle as it wishes, for example:

override fun onBackPressed(): Boolean {
    val childFragment = childFragmentManager.findFragmentByTag(SomeChildFragment::class.java.simpleName)
    if (childFragment != null && childFragment.isVisible) {
        // Only for that case, pop the BackStack (perhaps when other child fragments are visible don't)
        childFragmentManager.popBackStack()
        return true
    }
    return false
}

This allows to avoid thinking that there is some legitimate child fragment to remove when using a view pager for example (and back stack entry count > 0).