Android Navigation Component back button not working

问题

I'm using the Navigation Component in android where I have set 6 fragments initially. The problem is when I added a new fragment (ProfileFragment).

When I navigate to this new fragment from the start destination, pressing the native back button does not pop the current fragment off. Instead, it just stays to the fragment I'm in - the back button does nothing.

Here's my navigation.xml:

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/dashboard_navigation"
    app:startDestination="@id/dashboardFragment"
    >

                <fragment
                    android:id="@+id/dashboardFragment"
                    android:name="com.devssocial.localodge.ui.dashboard.ui.DashboardFragment"
                    android:label="DashboardFragment"
                    >
                                <action
                                    android:id="@+id/action_dashboardFragment_to_newPostFragment"
                                    app:destination="@id/newPostFragment"
                                    app:enterAnim="@anim/slide_in_up"
                                    app:exitAnim="@anim/slide_out_down"
                                    app:popEnterAnim="@anim/slide_in_up"
                                    app:popExitAnim="@anim/slide_out_down"
                                    />
                                <action
                                    android:id="@+id/action_dashboardFragment_to_notificationsFragment"
                                    app:destination="@id/notificationsFragment"
                                    app:enterAnim="@anim/slide_in_up"
                                    app:exitAnim="@anim/slide_out_down"
                                    app:popEnterAnim="@anim/slide_in_up"
                                    app:popExitAnim="@anim/slide_out_down"
                                    />
                                <action
                                    android:id="@+id/action_dashboardFragment_to_mediaViewer"
                                    app:destination="@id/mediaViewer"
                                    app:enterAnim="@anim/slide_in_up"
                                    app:exitAnim="@anim/slide_out_down"
                                    app:popEnterAnim="@anim/slide_in_up"
                                    app:popExitAnim="@anim/slide_out_down"
                                    />
                                <action
                                    android:id="@+id/action_dashboardFragment_to_postDetailFragment"
                                    app:destination="@id/postDetailFragment"
                                    app:enterAnim="@anim/slide_in_up"
                                    app:exitAnim="@anim/slide_out_down"
                                    app:popEnterAnim="@anim/slide_in_up"
                                    app:popExitAnim="@anim/slide_out_down"
                                    />

                            ====================== HERE'S THE PROFILE ACTION ====================                                
                                <action
                                    android:id="@+id/action_dashboardFragment_to_profileFragment"
                                    app:destination="@id/profileFragment"
                                    app:enterAnim="@anim/slide_in_up"
                                    app:exitAnim="@anim/slide_out_down"
                                    app:popEnterAnim="@anim/slide_in_up"
                                    app:popExitAnim="@anim/slide_out_down"
                                    />
                            =====================================================================                                

                </fragment>



                <fragment
                    android:id="@+id/profileFragment"
                    android:name="com.devssocial.localodge.ui.profile.ui.ProfileFragment"
                    android:label="fragment_profile"
                    tools:layout="@layout/fragment_profile"
                    />
</navigation>

In the image above, the highlighted arrow (in the left) is the navigation action I'm having troubles with.

In my Fragment code, I'm navigating as follows:

findNavController().navigate(R.id.action_dashboardFragment_to_profileFragment)

The other navigation actions are working as intended. But for some reason, this newly added fragment does not behave as intended.

There are no logs showing when I navigate to ProfileFragment and when I press the back button.

Am I missing something? or is there anything wrong with my action/fragment configurations?

EDIT: I do not do anything in ProfileFragment. Here's the code for it:

class ProfileFragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_profile, container, false)
    }


}

And my activity xml containing the nav host:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <fragment
            android:id="@+id/dashboard_navigation"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:navGraph="@navigation/dashboard_navigation"
            app:defaultNavHost="true"/>

</FrameLayout>

回答1:

You can use this following for the Activity

onBackPressedDispatcher.addCallback(
                this,
                object : OnBackPressedCallback(true) {
                    override fun handleOnBackPressed() {
                        onBackPressed()
                        // if you want onBackPressed() to be called as normal afterwards

                    }
                }
        )

For the fragment, It will be needed requireActivity() along with Callback

requireActivity().onBackPressedDispatcher.addCallback(
                    this,
                    object : OnBackPressedCallback(true) {
                        override fun handleOnBackPressed() {
                            requireActivity().onBackPressed()
                            // if you want onBackPressed() to be called as normal afterwards

                        }
                    }
            )

If you have a Button or something else to perform an action then you can use

this.findNavController().popBackStack()

来源：https://stackoverflow.com/questions/59834398/android-navigation-component-back-button-not-working