Android导航返回到标题屏幕

我的应用程序现在有三个屏幕：主页、火箭和公司。当我打开应用程序时，它会出现在主屏幕上，并有一个汉堡图标打开导航抽屉。问题是，当我从抽屉中选择Rockets或Company时，汉堡包图标会替换为back箭头。单击箭头将导航回主屏幕。当我在主屏幕上时，汉堡包图标再次出现

活动\u 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>

<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>

那么，如何使我的屏幕能够访问导航抽屉，而不是成为主屏幕的导航路径

---

换句话说，我希望我的屏幕能够通过导航抽屉转到另一个屏幕，而不是从该屏幕转到主屏幕，然后转到另一个屏幕。

似乎您的代码中没有使用

AppBarConfiguration

，这将解决您的问题

AppBarConfiguration： NavigationUI使用AppBarConfiguration对象管理应用程序显示区域左上角导航按钮的行为。导航按钮的行为会根据用户是否在顶级目的地而变化

请参阅文档以了解更多信息

我已经更新了您下面活动的代码。如果导航扩展函数显示错误，请确保在

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'

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()
        }
    }
}

更新的活动代码：

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'

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：如果您通过创建新项目（导航抽屉活动模板）来使用Android Studio4.1.2版，它将使用AppBarConfiguration和所有需要的依赖项来设置项目。所以你也可以试试。

太好了，现在可以用了。只剩下一件小事-汉堡图标在点击

Company

或

Rocket

后变为箭头，尽管其行为正常（打开抽屉）。@LeNguyenDuyAnh您是否使用导航抽屉活动模板创建了一个新项目？