（导航组件）返回首页片段时如何在活动上显示返回箭头？

Question

我必须分割折扣片段并编辑显示在“编辑服务”活动中的服务片段。当我返回编辑服务片段时，折扣片段上显示的后退箭头消失了我想显示它以从编辑服务活动中导航上一个活动。

活动布局 ..................................... …………

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 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">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <androidx.appcompat.widget.Toolbar

            android:id="@+id/toolbar_hesham"
            android:theme="@style/ThemeOverlay.AppCompat.ActionBar"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
            app:title="@string/edit_service"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@color/colorPrimary"
            android:minHeight="?attr/actionBarSize"
            app:layout_constraintTop_toTopOf="parent" />

        <fragment
            android:id="@+id/nav_host_edit_service"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            app:layout_constraintTop_toBottomOf="@+id/toolbar_hesham"
            app:layout_constraintBottom_toBottomOf="parent"
            app:defaultNavHost="true"
            app:navGraph="@navigation/edit_service_nav" />
    </androidx.constraintlayout.widget.ConstraintLayout>


    <include layout="@layout/confirm_request_bottom_sheet"/>
</androidx.coordinatorlayout.widget.CoordinatorLayout>

活动代码 ..................................... ………………

public class EditServicesActivity extends BaseActivity<MainViewModel> {


    public Toolbar toolbar;
    public NavController navController;

    @Override
    protected void initActivityComponent() {
        component = ProServeTechApp.getComponent(this)
                .plus(new ActivityModule(this));
        component.inject(this);
    }

    @Override
    protected int getLayout() {
        return R.layout.activity_edit_services;
    }

    @Override
    protected Class<MainViewModel> getViewModelClass() {
        return MainViewModel.class;
    }

    @Override
    protected void initActivity() {
        viewModel.getRequestDetails(getIntent().getExtras().getString("requestId"), String.valueOf(0));
        viewModel.getIssues(getIntent().getStringExtra("requestId"));

        toolbar = findViewById(R.id.toolbar_hesham);
        setSupportActionBar(toolbar);

        navController = Navigation.findNavController(this, R.id.nav_host_edit_service);
        NavigationUI.setupWithNavController(toolbar, navController );

    }



}

导航 ........................................

<?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/edit_service_nav"
    app:startDestination="@id/edi_service_fragment">

    <fragment
        android:id="@+id/edi_service_fragment"
        android:name="com.unicomg.proservetech.ui.requestdetails.edit.service.fragments.EditServiceFragment"
        android:label="@string/edit_service"
        tools:layout="@layout/edit_service_fragment">

        <action
            android:id="@+id/action_edi_service_fragment_to_discount_fragment"
            app:destination="@id/discount_fragment"
            app:enterAnim="@anim/slide_up"
            app:exitAnim="@anim/slide_bottom"
            app:popEnterAnim="@anim/slide_up"
            app:popExitAnim="@anim/slide_bottom" />
    </fragment>

    <fragment
        android:id="@+id/discount_fragment"
        android:name="com.unicomg.proservetech.ui.requestdetails.edit.service.fragments.DiscountFragment"
        android:label="@string/add_discount"
        tools:layout="@layout/discount_fragment">


    </fragment>

</navigation>

Answer 1

As per the setupWithNavController(Toolbar, NavController) documentation:

The start destination of your navigation graph is considered the only top level destination. On all other destinations, the Toolbar will show the Up button.

If you want to also show the Up button on your start destination (i.e., to go to the previous activity), you'd want to use the version that takes an AppBarConfiguration.

As per the Update UI components documentation on AppBarConfiguration, AppBarConfiguration allows you to set exactly what destinations you want as top level destinations. To get the Up button to show on every destination, you'd use an empty set of top level destinations:

AppBarConfiguration appBarConfiguration =
    new AppBarConfiguration.Builder().build();

Note that since you're using setSUpportActionBar(), you should follow the Action Bar documentation and use the setupActionBarWithNavController() method rather than the Toolbar version. You must also override onSupportNavigateUp() to handle the up button.

Therefore your complete code would look like:

public class EditServicesActivity extends BaseActivity<MainViewModel> {


    public Toolbar toolbar;
    public AppBarConfiguation appBarConfiguation;
    public NavController navController;

    @Override
    protected void initActivityComponent() {
        component = ProServeTechApp.getComponent(this)
                .plus(new ActivityModule(this));
        component.inject(this);
    }

    @Override
    protected int getLayout() {
        return R.layout.activity_edit_services;
    }

    @Override
    protected Class<MainViewModel> getViewModelClass() {
        return MainViewModel.class;
    }

    @Override
    protected void initActivity() {
        viewModel.getRequestDetails(getIntent().getExtras().getString("requestId"), String.valueOf(0));
        viewModel.getIssues(getIntent().getStringExtra("requestId"));

        toolbar = findViewById(R.id.toolbar_hesham);
        setSupportActionBar(toolbar);

        navController = Navigation.findNavController(this, R.id.nav_host_edit_service);
        appBarConfiguration = new AppBarConfiguration.Builder().build();
        NavigationUI.setupActionBarWithNavController(this, navController,
            appBarConfiguration);
    }

    @Override
    public boolean onSupportNavigateUp() {
        return NavigationUI.navigateUp(navController, appBarConfiguration)
                || super.onSupportNavigateUp();
    }
}