Passing Interface To Fragment From Activity

Question

I am trying to send information from fragment to the main activity.

I am trying to set a var interfaceName in a fragment from the main activity.

I created var menuInterface: MenuInterface and tried to set it in onNavigationItemSelected using myFragment.menuInterface = this

The menuInterface stays null for some reason... any idea why?

the onNavigationItemSelected

override fun onNavigationItemSelected(menuItem: MenuItem): Boolean {
    when (menuItem.itemId) {
        R.id.feedLayoutId -> {
            feedFragment = FeedFragment()
            feedFragment.menuInterface = this
            barTitle.text = "myTitle"
            supportFragmentManager
                .beginTransaction()
                .replace(R.id.frame_layout, feedFragment)
                .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
                .commit()
        }
    }
    drawerLayout.closeDrawer(GravityCompat.START)
    return true
}

why should you send the interface to the fragment? If you wanna send data from activity to fragment, you should use a bundle. If you wanna notify activity from fragment, you should use an interface. — rafaelasguerra, Dec 23 '19 at 14:42
Just implement suppose interface A in your activity and in ur fragment's onAttach method typecast context to interface A. — Prateek Kumar, Dec 23 '19 at 14:47
tried `class FeedFragment(menuInterface: MenuInterface)` but i cant use the `menuInterface` for some reason — zion.b., Dec 23 '19 at 14:57
@rguerra i am trying to send information from the fragment to the activity — zion.b., Dec 23 '19 at 14:58
Would that help: https://stackoverflow.com/questions/18579590/how-to-send-data-from-dialogfragment-to-a-fragment/18579638#18579638 — Marcin Orlowski, Dec 23 '19 at 15:09

Prateek Kumar · Accepted Answer · 2020-06-03T15:35:40.127

3

Implement MenuInterface in your activity,and remove this line from ur code.

feedFragment.menuInterface = this

In ur fragment:

private var menuInterface: MenuInterface? = null

override fun onAttach(context: Context?) {
    super.onAttach(context)
    menuInterface = context as MenuInterface
}

override fun onDetach() {
    menuInterface = null
    super.onDetach()
}

edited Jun 03 '20 at 15:35

answered Dec 23 '19 at 15:07

Prateek Kumar

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1

do not forget to call on detach – rafaelasguerra Dec 24 '19 at 09:42

score 0 · Answer 2 · answered Dec 23 '19 at 15:05

I have already provided solution for such question. https://stackoverflow.com/a/35038574/3027124

The idea is communication between activity and fragment should be done through interfaces or you should implement MVVM architecture and use the same view model for both fragment and activity.

Useful resources:

Passing Interface To Fragment From Activity

2 Answers2