How to prevent previous fragment to show up after pressing back button using navigation controller?

问题

I am trying to use the navigation controller right now. I want to move from LoginFragment to HomeFragment. In LoginFragment I use this code below to move to HomeFragment.

Navigation.findNavController(view).navigate(homeDestination)

However, when I tap the back button in the HomeFragment, it will go back to LoginFragment, I expect that when I tap the button it will close the app.

In old way, if I use activity instead of using Fragment, I usually do something like this to get that expected behaviour:

val intent = Intent(this,HomeActivity::class.java)
intent.flags = Intent.FLAG_ACTIVITY_CLEAR_TASK.or(Intent.FLAG_ACTIVITY_NEW_TASK)
startActivity(intent)

By using those flags, I use to get the expected behavior. But I don't how to implement the same behavior using the navigation controller.

回答1:

Navigation offers a popUpTo and popUpToInclusive attributes for removing fragments from the back stack as part of a navigate() operation.

This can be set either in XML:

<!-- Add to your Navigation XML, then use navigate(R.id.go_home) -->
<action
  android:id="@+id/go_home"
  app:destination="@+id/home_fragment"
  app:popUpTo="@+id/destination_to_pop"
  app:popUpToInclusive="true"/>

Or set it programmatically:

NavOptions navOptions = new NavOptions.Builder()
    .setPopUpTo(R.id.destination_to_pop, true)
    .build();
Navigation.findNavController(view).navigate(homeDestination, navOptions)

You can also use the id of a <navigation> element as well.

回答2:

I think this should do the trick.

NavController controller = Navigation.findNavController(view);
controller.popBackStack(R.id.fragmentLogin, true);
controller.navigate(homeDestination)

来源：https://stackoverflow.com/questions/54919101/how-to-prevent-previous-fragment-to-show-up-after-pressing-back-button-using-nav