How to handle up button inside fragment using Navigation Components

Question

I am making a simple note taking app, I have 2 fragments with navigation component, one fragment has a list of notes and the other is for editing or creating a new note.

In MainActivity I added

val navController = this.findNavController(R.id.host_fragment)
NavigationUI.setupActionBarWithNavController(this, navController)

and then override onSupportNavigateUp()

override fun onSupportNavigateUp(): Boolean {
        val navController = this.findNavController(R.id.host_fragment)
        return navController.navigateUp()
    }

In NoteEditFragment

requireActivity().onBackPressedDispatcher.addCallback(this) {
        saveOrUpdateNote(noteId, note)
    }

now it all works well when pressing the "back button" in the device, However onBackPressedDispatcher.addCallback() is note triggered when I press the "up button" the one on the top left of the screen.

My question is : How do I handle this up button from my NoteEditFragment?

Thanks in advance

Answer 1

Finally, I found the solution.

First In the activity onCreate method I had to connect the navigation like I did:

val navController = this.findNavController(R.id.host_fragment)
NavigationUI.setupActionBarWithNavController(this, navController)

Then still in MainActivity override onSupportNavigateUp() :

override fun onSupportNavigateUp(): Boolean
{
    val navController = this.findNavController(R.id.host_fragment)
    return navController.navigateUp()
}

Then In the Fragment onCreateView I had to enable option menu:

setHasOptionsMenu(true)

then in the fragment I overridden onOptionsItemSelected :

override fun onOptionsItemSelected(item: MenuItem): Boolean
{
    // handle the up button here
    return NavigationUI.onNavDestinationSelected(item!!,
        view!!.findNavController())
            || super.onOptionsItemSelected(item)
}

Note: I think if you have more than one option menu, then I think you have to do a when (item) statement to check what option has been chosen.

Also if you want to handle the device back button then you can do like this in your fragment onCreateViewMethod :

requireActivity().onBackPressedDispatcher.addCallback(this)
    {
        // handle back button

// change this line to whatever way you chose to navigate back          
findNavController().navigate(NoteEditFragmentDirections.actionNoteEditFragmentToNoteListFragment())
        }