NavigationUI 在 Home Destination 上显示后退（向上）按钮

Question

我正在尝试使用 Action Bar 实现 NavigationUI。我无法摆脱 startDestination 上的后退按钮。

我尝试了 getActionBar().setDisplayShowHomeEnabled(false); 和 getActionBar().setHomeButtonEnabled(false); 但是 getActionBar() returns null。我是 Android 编程新手，找不到解决方案。任何帮助表示赞赏。谢谢。

主要Activity:

public class MainActivity extends AppCompatActivity {

    NavController navController;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        navController = Navigation.findNavController(this, R.id.my_nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this,  navController);
    }


    @Override
    public boolean onSupportNavigateUp() {
        navController.navigateUp();
        return super.onSupportNavigateUp();
    }
}

主要Activity布局：

<fragment
    android:id="@+id/my_nav_host_fragment"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:defaultNavHost="true"
    app:navGraph="@navigation/app_navigation" />

NavGraph 与 startDestination:

<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/app_navigation.xml"
    app:startDestination="@id/mainFragment">
    <fragment
        android:id="@+id/mainFragment"
        android:name="com.tarpinyan.navigationui_test.MainFragment"
        android:label="MainFragment" >
        <action
            android:id="@+id/action_mainFragment_to_timerFragment"
            app:destination="@id/timerFragment" />
        <action
            android:id="@+id/action_mainFragment_to_settingFragment"
            app:destination="@id/settingFragment" />
        <action
            android:id="@+id/action_mainFragment_to_addFragment"
            app:destination="@id/addFragment" />
    </fragment>
    <fragment
        android:id="@+id/settingFragment"
        android:name="com.tarpinyan.navigationui_test.SettingFragment"
        android:label="SettingFragment" />
    <fragment
        android:id="@+id/addFragment"
        android:name="com.tarpinyan.navigationui_test.AddFragment"
        android:label="AddFragment" />
    <fragment
        android:id="@+id/timerFragment"
        android:name="com.tarpinyan.navigationui_test.TimerFragment"
        android:label="TimerFragment" />
</navigation>

主要片段：

public class MainFragment extends Fragment {

    @Nullable
    @org.jetbrains.annotations.Nullable
    @Override
    public View onCreateView(@NonNull @NotNull LayoutInflater inflater, @Nullable @org.jetbrains.annotations.Nullable ViewGroup container, @Nullable @org.jetbrains.annotations.Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_main, container, false);
        setHasOptionsMenu(true);

        
        return view;
    }


    @Override
    public void onCreateOptionsMenu(@NonNull @NotNull Menu menu, @NonNull @NotNull MenuInflater inflater) {
        inflater.inflate(R.menu.main_menu, menu);
    }


    @Override
    public boolean onOptionsItemSelected(@NonNull @NotNull MenuItem item) {
        if (item.getItemId() == R.id.menu_settings) {
            NavHostFragment.findNavController(this).navigate(R.id.action_mainFragment_to_settingFragment);
        }
        return true;
    }
}

Main Fragment with the back button

Answer 1

要从第一个片段中删除向上按钮，您需要使用 setupActionBarWithNavController() 方法的 3 参数版本，该方法采用 AppBarConfiguration，您可以在其中指定要删除的片段向上按钮来自.

AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
            R.id.mainFragment) // Remove Up button from mainFragment 
            .build();

setupActionBarWithNavController(this,  navController, appBarConfiguration);

更新：

the result is the same, I implemented the 3 arg version but still Main Fragment appears with the up button

听起来您明确启用了在主要片段中显示向上按钮。您需要确保在您的 mainFragment 中未启用 setDisplayHomeAsUpEnabled(true)。

或者您可以通过以下方式明确禁用它：

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {
    ((AppCompatActivity)requireActivity()).getSupportActionBar()
                       .setDisplayHomeAsUpEnabled(false); // Hide the UP button

    // ....
}

NavigationUI 在 Home Destination 上显示后退（向上）按钮

NavigationUI shows back (up) button on Home Destination

java

navigation

android

appbar

android-architecture-navigation