Bottom Navigation with Drawer Layout | onBackPressed in Fragment

Question

I have an interesting and confusing question.

I have a Drawer Layout that opens from the Bottom Navigation like in the photo

Screens:

In order for Drawer Layout to open from the Bottom Navigation, I used this code:

    bottomNavigationView.setOnItemSelectedListener { item ->
            when (item.itemId) {
                R.id.itemDrawer -> {
                    drawerLayout.openDrawer(GravityCompat.END)
                    return@setOnItemSelectedListener false
                }
                R.id.homeFragment -> navController.navigate(R.id.homeFragment)
                R.id.booksFragment -> navController.navigate(R.id.booksFragment)
                R.id.grammarFragment -> navController.navigate(R.id.grammarFragment)
                R.id.translatorFragment -> navController.navigate(R.id.translatorFragment)
            }
            true
        }

This is what my problem is

When I override listener for Bottom Navigation, in my opinion, the onBackPressed behaviour gets confused default.

I mean that when I click on Home, then another element, then Home again, and so on several times, and I stay on the Home Fragment and click on onBackPressed, then instead of leaving the app, I go back to the fragment where I was before

I think this is not normal for the user

What should I do?

I thought to somehow override onBackPressed for Home Fragment but I don't understand how to do it

Putra Nugraha · Accepted Answer · 2021-11-04 22:48:17Z

2

You can use onBackPressedDispatcher in your HomeFragment

private lateinit var onBackPressedCallback: OnBackPressedCallback

and instantiate the implementation and add the callback to activity in onResume()

override fun onResume() {
    super.onResume()
    onBackPressedCallback = object : OnBackPressedCallback(true) {
            override fun handleOnBackPressed() {
                activity?.moveTaskToBack(true)
                exitProcess(ZERO)
            }
        }
    
    activity?.onBackPressedDispatcher?.addCallback(onBackPressedCallback)
}

Due to this callback added on activity, then the callback should be removed on leaving HomeFragment

override fun onPause() {
    onBackPressedCallback.remove()
    super.onPause()
}

edited Nov 4, 2021 at 22:48

answered Nov 3, 2021 at 23:55

Putra Nugraha

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3 Comments

Mihail Palminschi Over a year ago

Thanks for the answer, I have already tried with addCallback, but the problem is that when I switch to another fragment, this сallback remains, and it turns out that my app can be closed from all fragments.

Mihail Palminschi Over a year ago

Should I somehow remove this callback when the fragment is closed? How can i do this?

Putra Nugraha Over a year ago

Yeah, need to add remove() for the callback as well, I've updated the answer. Thanks

Mihail Palminschi · Accepted Answer · 2021-11-04 18:52:20Z

0

I found the answer.

Everything is as in the selected answer, but need to remove this callback in the onPause of this fragment. To prevent the app from closing from all fragments

1. Create a variable for callback

private lateinit var mCallback: OnBackPressedCallback

2. In onViewCreated :

mCallback = object : OnBackPressedCallback(true) {
            override fun handleOnBackPressed() {
                activity?.moveTaskToBack(true)
                exitProcess(0)
            }
        }

activity?.onBackPressedDispatcher?.addCallback(mCallback)

3. Remove callback when closing the fragment

 override fun onPause() {
        mCallback.remove()
        super.onPause()
    }

edited Nov 4, 2021 at 18:52

answered Nov 4, 2021 at 18:19

Mihail Palminschi

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