单击抽屉后如何继续显示汉堡包图标而不是 back/up 图标？

Question

我正在关注代码实验室 https://developer.android.com/codelabs/kotlin-android-training-add-navigation/index.html#9，我使用以下代码连接抽屉：

class MainActivity : AppCompatActivity() {

    private lateinit var drawerLayout : DrawerLayout

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        @Suppress("UNUSED_VARIABLE")
        val binding = DataBindingUtil.setContentView<ActivityMainBinding>(this, R.layout.activity_main)
        drawerLayout = binding.drawerLayout

        val navController = findNavController(R.id.myNavHostFragment)
        // To support up action and also the title, the third parameter is optional and is used
        // for the hamburger menu for drawer.
        NavigationUI.setupActionBarWithNavController(this, navController, drawerLayout)

        // show the navigation drawer
        NavigationUI.setupWithNavController(binding.navView, navController)
    }

    override fun onSupportNavigateUp(): Boolean {
        val navController = findNavController(R.id.myNavHostFragment)

        // this is for the hamburger menu
        return NavigationUI.navigateUp(navController, drawerLayout)
    }
}

显示初始片段时，汉堡包按预期显示：

但是，在我从抽屉中选择了一件物品之后，例如左右，变成了back/up按钮：

如何继续使用汉堡包按钮而不是将其更改为向上按钮？

代码实验室的完整代码在这里：https://github.com/google-developer-training/android-kotlin-fundamentals-apps/tree/master/AndroidTriviaNavigation

Answer 1

我认为如果您在 navdrawer_menu.xml 文件中添加布局，汉堡包图标将保留

Answer 2

根据 AppBarConfiguration documentation:

NavigationUI uses an AppBarConfiguration object to manage the behavior of the Navigation button in the upper-left corner of your app's display area. The Navigation button’s behavior changes depending on whether the user is at a top-level destination.

A top-level destination is the root, or highest level destination, in a set of hierarchically-related destinations. Top-level destinations do not display an Up button in the top app bar because there is no higher level destination. By default, the start destination of your app is the only top-level destination.

When the user is at a top-level destination, the Navigation button becomes a drawer icon if the destination uses a DrawerLayout. If the destination doesn't use a DrawerLayout, the Navigation button is hidden. When the user is on any other destination, the Navigation button appears as an Up button.

因此，如果您想让抽屉图标出现在多个目的地而不仅仅是起始目的地，您需要创建一个 AppBarConfiguration 对象，其中包含您希望成为顶级目的地的确切目的地：

// Use the IDs from your navigation graph
val appBarConfiguration = AppBarConfiguration(
    setOf(R.id.rulesFragment, R.id.aboutFragment),
    drawerLayout)

因此，您的代码变为：

class MainActivity : AppCompatActivity() {

    private lateinit var appBarConfiguration : AppBarConfiguration

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        @Suppress("UNUSED_VARIABLE")
        val binding = DataBindingUtil.setContentView<ActivityMainBinding>(this, R.layout.activity_main)
        // Use the Kotlin extension in navigation-ui-ktx to create
        // the AppBarConfiguration
        appBarConfiguration = AppBarConfiguration(
            setOf(R.id.rulesFragment, R.id.aboutFragment),
            binding.drawerlayout)

        val navController = findNavController(R.id.myNavHostFragment)
        // To support up action and also the title, the third parameter is optional and is used
        // for the hamburger menu for drawer.
        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration)

        // show the navigation drawer
        NavigationUI.setupWithNavController(binding.navView, navController)
    }

    override fun onSupportNavigateUp(): Boolean {
        val navController = findNavController(R.id.myNavHostFragment)

        // this is for the hamburger menu
        return NavigationUI.navigateUp(navController, appBarConfiguration)
    }
}