How I can retrieve current fragment in NavHostFrag

问题:

I tried to find a method in the new Navigation components but I didn't find anything about that.

I have the current destination with :

mainHostFragment.findNavController().currentDestination

But I can't get any reference to the displayed fragment.

回答1:

Navigation does not provide any mechanism for getting the implementation (i.e., the Fragment itself) of the current destination.

As per the Creating event callbacks to the activity, you should either communicate with your Fragment by

• Having the Fragment register a callback in its onAttach method, casting your Activity to an instance of an interface you provide
• Use a shared ViewModel that your Activity and Fragment use to communicate.

回答2:

You can do something like this:

  override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)

        val navHostFragment = supportFragmentManager.fragments.first() as? NavHostFragment
        if(navHostFragment != null) {
            val childFragments = navHostFragment.childFragmentManager.fragments
            childFragments.forEach { fragment ->
                fragment.onActivityResult(requestCode, resultCode, data)
            }
        }
    }

But for more advanced communication Listeners with callback methods registered in Fragment.onAttach() (Fragment -> Activity rather one direction communication) and SharedViewModel (bidirectional, important to have ViewModelProviders, and Lifecycle owner that is scoped to getActivity() rather)

回答3:

Using Michal's answer I wrote this extension function for testing:

@Suppress("UNCHECKED_CAST")
fun <F : Fragment> AppCompatActivity.getFragment(fragmentClass: Class<F>): F? {
    val navHostFragment = this.supportFragmentManager.fragments.first() as NavHostFragment

    navHostFragment.childFragmentManager.fragments.forEach {
        if (fragmentClass.isAssignableFrom(it.javaClass)) {
            return it as F
        }
    }

    return null
}

Used like this:

val myFragment = activity.getFragment(MyFragment::class.java)