How I can retrieve current fragment in NavHostFragment?

Question

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.

Solution 1

Reference to the displayed fragment (AndroidX):

java

public Fragment getForegroundFragment(){
    Fragment navHostFragment = getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
    return navHostFragment == null ? null : navHostFragment.getChildFragmentManager().getFragments().get(0);
}

kotlin

val navHostFragment: Fragment? =
        supportFragmentManager.findFragmentById(R.id.nav_host_fragment)
navHostFragment?.childFragmentManager?.fragments?.get(0)

Here nav_host_fragment is an ID of the fragment tag in your activity_main.xml with android:name="androidx.navigation.fragment.NavHostFragment"

Solution 2

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.

Solution 3

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)

Solution 4

Based on other answers

Fragment navHostFragment = getSupportFragmentManager().getPrimaryNavigationFragment();
Fragment fragment = navHostFragment.getChildFragmentManager().getFragments().get(0);

((Your Fragment Class) fragment).(public method inside the fragment)

worked for me

Solution 5

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)

View more solutions

Comments

[Sever]

All links show how to communicate between fragments. But how we can call fragment method from activity if navigation does not provide any mechanism for getting the implementation of the current destination?

[ianhanniballake]

@Sever - see this issue and how to use getPrimaryNavigationFragment() to retrieve the current Fragment.

[Sever]

Big thanks. It works. val navHostFragment = supportFragmentManager.primaryNavigationFragment as NavHostFragment val yourFragment = currentFragmentClassName.childFragmentManager.primaryNavigat‌​ionFragment as YourFragment

[drdaanger]

You can squish this down to inline fun <reified T : Fragment> FragmentManager.findFragmentByClass(): T? = fragments.firstOrNull { it is T } as T?

[isabsent]

@ianhanniballake: Sorry, I didn't understand is there a way to get the foreground fragment by means of getPrimaryNavigationFragment() now or they are going to provide such opportunity in the future only!?

[Miha_x64]

Well, to share ViewModel between two fragments, one of them must be its owner. And the other one must find that owner in order to fetch that ViewModel. So… just never use Navigation, it's retarded.

[carl]

It is incomprehensible why Navigation does not maintain a list of fragments, for example needed when MainActivity wants to call a method in a child fragment. In consequence, you need to use the "good old ways" for that, and then, whats the point of introducing a Navigation system? I don@t get it.

[Shalbert]

You can remove as? NavHostFragment and make the if-statement if (navHostFragment is NavHostFragment)

[Milad Faridnia]

in my case ?.childFragmentManager?.fragments?.last() gives me current fragment

[John Glen]

Wow, hacky answers. childFragmentManager.findFragmentById exists.