Android Fragment Navigation Custom Navigation Back Button

Question

I need to navigate a stack of fragments and I am navigating back using the toolbar back button. Can I override the back button pressed to set a custom animation, for example slide out?

Here is the code for the toolbar.

private fun setupToolbar() {
    val appBarConfiguration = AppBarConfiguration(navController.graph, drawer_layout)
    val toolbar = toolbar as Toolbar
    setSupportActionBar(toolbar)
    toolbar.setupWithNavController(navController, appBarConfiguration)
    val ab: ActionBar? = supportActionBar
    ab?.setDisplayShowTitleEnabled(false) // disable the default title element here (for centered title)
    setupSearchQueryListener()
}

You can do so by overriding onBackPressed in your hosting activity then using an interface as a listener if i understand what you're asking correctly — tendai
– tendai, Commented May 12, 2020 at 8:51
Hmm. seems like the onBackPressed is only activated when I press the "physical" back button on my phone? — Casper Lindberg
– Casper Lindberg, Commented May 12, 2020 at 8:56
you can create a custom toolbar, register a clickListener with your custom toolbar back button then trigger the interface in your onclick event or just trigger the interface in your current toolbar's back button event. make sense? — tendai
– tendai, Commented May 12, 2020 at 9:04
Is it possible to use the default toolbar and in some way access the back button anyway? — Casper Lindberg
– Casper Lindberg, Commented May 12, 2020 at 10:43

ror · Accepted Answer · 2020-05-16 15:02:59Z

In your setup code, one more thing is needed:

    toolbar.setNavigationOnClickListener {
        onBackPressedDispatcher.onBackPressed() 
    }

In your fragments, you could do this:

    protected lateinit var backPressedCallback: OnBackPressedCallback

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        backPressedCallback = requireActivity().onBackPressedDispatcher.addCallback(this) {
            // your code
        }
    }

The above will enable you to intercept back navigation uniformly and execute your code in question (you can even block/unblock it by playing with backPressedCallback.isEnabled flag). The above was tested. Speaking of setting navigation animation, I was only playing with xml defined action based animations:

        <action
            android:id="@+id/toYourDest"
            app:destination="@+id/yourDest"
            app:enterAnim="@anim/your_slide_in_right"
            app:exitAnim="@anim/your_slide_out_left"
            app:popEnterAnim="@anim/your_slide_in_left"
            app:popExitAnim="@anim/your_slide_out_right" />

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