Android 导航返回标题屏幕

Question

我的应用现在有三个屏幕：主页、火箭和公司。当我打开应用程序时，它在主屏幕上，并且有一个汉堡图标可以打开导航抽屉。问题是当我从抽屉中选择 Rockets 或 Company 时，汉堡包图标被一个后退箭头替换。单击箭头将导航回主屏幕。当我在主屏幕上时，汉堡图标会重新出现。

activity_main.xml:

<androidx.drawerlayout.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar_main"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/midnight_blue" />

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

    </LinearLayout>

    <com.google.android.material.navigation.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_header"
        app:menu="@menu/nav_menu"
        />

</androidx.drawerlayout.widget.DrawerLayout>

nav_menu.xml:

<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:id="@+id/homeFragment"
        android:icon="@drawable/ic_home"
        android:title="@string/nav_menu_home"
        />

    <group
        android:id="@+id/group_data"
        >
        <item
            android:id="@+id/rocketsDataFragment"
            android:icon="@drawable/ic_rocket"
            android:title="@string/nav_menu_rockets_data"
            />

        <item
            android:id="@+id/companyDataFragment"
            android:icon="@drawable/ic_company"
            android:title="@string/nav_menu_company_data"
            />
    </group>

    <group
        android:id="@+id/group_launches"
        >
        <item
            android:id="@+id/past_launches"
            android:icon="@drawable/ic_prev"
            android:title="@string/nav_menu_launches_past"
            />

        <item
            android:id="@+id/upcoming_launches"
            android:icon="@drawable/ic_next"
            android:title="@string/nav_menu_launches_upcoming"
            />
    </group>

</menu>

nav_graph.xml

<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/nav_graph"
    app:startDestination="@id/homeFragment"
    >

    <fragment
        android:id="@+id/homeFragment"
        android:name="com.example.rocketman.home.HomeFragment"
        android:label="@string/nav_menu_home"
        tools:layout="@layout/fragment_home"
        />

    <fragment
        android:id="@+id/rocketsDataFragment"
        android:name="com.example.rocketman.rocket.RocketsDataFragment"
        android:label="@string/nav_menu_rockets_data"
        tools:layout="@layout/fragment_rockets_data"
        />

    <fragment
        android:id="@+id/companyDataFragment"
        android:name="com.example.rocketman.company.CompanyDataFragment"
        android:label="@string/nav_menu_company_data"
        tools:layout="@layout/fragment_company_data"
        />

</navigation>

最后，MainActivity:

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private val navController by lazy {
        (supportFragmentManager
            .findFragmentById(R.id.fragment_nav_host) as NavHostFragment).navController
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        setSupportActionBar(binding.toolbarMain)
        setupNavigationDrawer()
    }

    private fun setupNavigationDrawer() {
        navController.let { navController ->
            NavigationUI.setupActionBarWithNavController(
                this,
                navController,
                binding.drawerLayout
            )
            NavigationUI.setupWithNavController(binding.navView, navController)
        }
    }

    override fun onSupportNavigateUp(): Boolean {
        return NavigationUI.navigateUp(navController, binding.drawerLayout)
    }

    override fun onBackPressed() {
        if(binding.drawerLayout.isDrawerOpen(GravityCompat.START)) {
            binding.drawerLayout.closeDrawer(GravityCompat.START)
        } else {
            super.onBackPressed()
        }
    }
}

那么我怎样才能让我的屏幕可以访问导航抽屉而不是主屏幕的导航路径？

换句话说，我希望我的屏幕都能够通过导航抽屉转到另一个屏幕，而不是从那个屏幕转到主屏幕，然后再转到另一个屏幕。

Answer 1

您似乎没有在代码中使用AppBarConfiguration 来解决您的问题。

AppBarConfiguration： NavigationUI 使用 AppBarConfiguration 对象来管理应用显示区域左上角的导航按钮的行为。导航按钮的行为会根据用户是否位于顶级目的地而改变。

请参阅文档以了解更多信息Update UI components with NavigationUI

我已在下方更新了您的活动代码。如果 Navigation Extensions Functions 显示错误，请确保您的 build.gradle 文件中有这些依赖项。

依赖关系：

implementation 'androidx.navigation:navigation-fragment-ktx:2.3.3'
implementation 'androidx.navigation:navigation-ui-ktx:2.3.3'
implementation 'androidx.navigation:navigation-fragment-ktx:2.3.3'
implementation 'androidx.navigation:navigation-ui-ktx:2.3.3'

更新的活动代码：

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private lateinit var appBarConfiguration: AppBarConfiguration
    private val navController by lazy {
        (supportFragmentManager
            .findFragmentById(R.id.fragment_nav_host) as NavHostFragment).navController
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        setSupportActionBar(binding.toolbarMain)
        setupNavigationDrawer()
    }

    private fun setupNavigationDrawer() {
        navController.let { navController ->
            // Passing each menu ID as a set of Ids because each
            // menu should be considered as top level destinations.
            appBarConfiguration = AppBarConfiguration(setOf(
                    R.id.homeFragment, R.id.rocketsDataFragment, R.id.companyDataFragment), binding.drawerLayout)
            setupActionBarWithNavController(navController, appBarConfiguration)

        binding.navView.setupWithNavController(navController)
      
        }     
    }

    override fun onSupportNavigateUp(): Boolean {
        return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
    }

    override fun onBackPressed() {
        if(binding.drawerLayout.isDrawerOpen(GravityCompat.START)) {
            binding.drawerLayout.closeDrawer(GravityCompat.START)
        } else {
            super.onBackPressed()
        }
    }
}

注意：如果您使用 Android Studio 版本 4.1.2 创建一个新项目（导航抽屉活动模板），它将使用 AppBarConfiguration 设置项目需要的依赖。所以你也可以试试。