Navigation Architecture Component - Login screen

问题

I am planning to implement navigation like this:

The problem I face is when user is in LoginFragmennt and presses back button it again loads up LognFragment ie. stuck in loop.

I navigate to LoginnFragment using conditional navigation as per this answer.

How to properly implement this?

回答1:

One of the solutions that i can propose is to override inside your activity onBackPressed method, and finish the activity if your current destination(before on back pressed handled) is login fragment.

override fun onBackPressed() {
    val currentDestination=NavHostFragment.findNavController(nav_host_fragment).currentDestination
    when(currentDestination.id) {
        R.id.loginFragment -> {
            finish()
        }
    }
    super.onBackPressed()
}

回答2:

IMHO how I do it in my app is a little cleaner. Just add these settings in the nav graph:

<fragment
    android:id="@+id/profile_dest"
    android:name="com.example.ProfileFragment">
    <action
        android:id="@+id/action_profile_dest_to_login_dest"
        app:destination="@id/login_dest"
        app:popUpTo="@+id/profile_dest"
        app:popUpToInclusive="true" />       
</fragment>

and then navigate to login via

findNavController().navigate(R.id.action_profile_dest_to_login_dest).

popUpTo and popUpToInclusive close ProfileFragment when we navigate to LoginFragment so if the user navigates back, it exits the app.

来源：https://stackoverflow.com/questions/51582674/navigation-architecture-component-login-screen