如何在嵌套图中从第三级导航回第二级？

Question

我有一个带有Navigation Drawer 的Single Activity 项目。我通过Navigation Components实现了导航的可能性。我创建了一个nav_graph.xml，它可以从Navigation Drawer 路由和打开每个Fragment。对于一级路由就足够了。但我的项目有两级，有时是三级路由。所以我为 nav_nested_settings 创建了一个嵌套导航图。

<?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/nav_graph"
    app:startDestination="@id/nav_fragment_home">

    <fragment
        android:id="@+id/nav_fragment_home"
        android:name="com.app.ui.fragment.home.HomeFragment"
        android:label="@string/nav_home"
        tools:layout="@layout/fragment_home">
        // other actions ...
        <action
            android:id="@+id/action_nav_fragment_home_to_nav_fragment_fragment"
            app:destination="@id/nav_nested_settings" />
    </fragment>
    // ... other fragments
    <fragment
        android:id="@+id/nav_fragment_search"
        android:name="com.app.ui.fragment.search.SearchFragment"
        android:label="@string/nav_search"
        tools:layout="@layout/fragment_search" />
    <include app:graph="@navigation/nav_settings" />
</navigation>

嵌套图是：

<?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:tool="http://schemas.android.com/tools"
    android:id="@+id/nav_nested_settings"
    android:label="@string/nav_settings"
    app:startDestination="@id/nav_fragment_settings">
    <fragment
        android:id="@+id/nav_fragment_settings"
        android:name="com.app.ui.fragment.settings.main.SettingsFragment"
        android:label="@string/nav_settings"
        tool:layout="@layout/fragment_settings">
        <action
            android:id="@+id/action_nav_fragment_settings_to_nav_fragment_settings_ads"
            app:destination="@id/nav_fragment_settings_ads" />
        <action
            android:id="@+id/action_nav_fragment_settings_to_nav_fragment_settings_app"
            app:destination="@id/nav_fragment_settings_app" />
        <action
            android:id="@+id/action_nav_fragment_settings_to_nav_fragment_settings_home"
            app:destination="@id/nav_fragment_settings_home" />
    </fragment>
    <fragment
        android:id="@+id/nav_fragment_settings_ads"
        android:name="com.app.ui.fragment.settings.ads.SettingsAdsFragment"
        android:label="@string/nav_settings_ads"
        tool:layout="@layout/fragment_settings_ads" />
    <fragment
        android:id="@+id/nav_fragment_settings_app"
        android:name="com.app.ui.fragment.settings.app.SettingsAppFragment"
        android:label="@string/nav_settings_app"
        tool:layout="@layout/fragment_settings_app" />
    <fragment
        android:id="@+id/nav_fragment_settings_home"
        android:name="com.app.ui.fragment.settings.home.SettingsHomeFragment"
        android:label="@string/nav_settings_home"
        tool:layout="@layout/fragment_settings_home">
    </fragment>
</navigation>

如果我从Navigation Drawer 中选择Settings，应用程序会打开它。然后我点击ads / app / home 按钮并打开下一个Fragment。但是，如果我点击应用工具栏中的back 按钮或箭头 - 什么都不会发生。

如何解决这个问题？如何在嵌套图中从第三级导航回第二级？

更新 01 // 添加了设置 NavController 和 AppBarConfiguration 的函数

private fun initNavigation() {
        mNavController = findNavController(R.id.navHostFragment)
        navView.setupWithNavController(mNavController)
        mAppBarConfiguration = AppBarConfiguration(mNavController.graph, drawerLayout)
        setupActionBarWithNavController(mNavController, mAppBarConfiguration)
}

更新02 我发现了一件有用的事情/错误。后退按钮工作正常，无需任何额外代码。但是，当我单击后退按钮时，应用程序会重复前面的操作“例如，从 SettingsFragment 转到 SettingsAdsFragment”。 我使用带有默认策略的 moxy lib - AddToEndSingleStrategy。

Answer 1

根据您的评论，我认为您的 onSupportNavigateUp() 并不完全正确。我已经用navDrawer和导航实现了几个应用程序，我覆盖onSupportNavigateUp()的方式如下：

// the activity hosting your navigation
class HostActivity : AppCompatActivity {
    // flag if for the currently shown fragment, navigating up is enabled
    // should be false for top level fragments, i.e. those accessible from navDrawer
    // should be set to true for lower level fragments
    private var canNavigateUp: Boolean = false
    
    ...

    override fun onSupportNavigateUp(): Boolean {
        return if (canNavigateUp) {
            mNavController.navigateUp()
        } else {
            NavigationUI.navigateUp(mNavController, mAppBarConfiguration)
        }
    }

    fun setNavigation(navigateUpEnabled: Boolean) {
        supportActionBar?.let { actionBar ->
            canNavigateUp = navigateUpEnabled
            if (navigateUpEnabled) {
                // set up icon
                actionBar.setHomeAsUpIndicator(null)
                lockUnlockDrawer(lock = true)
            } else {
                // set drawer icon
                actionBar.setDisplayShowHomeEnabled(true)
                lockUnlockDrawer(lock = false)
            }
        }
    }
}

然后，对于顶级片段，即可以直接从 navDrawer 访问的片段：

class TopLevelFragment : Fragment() {
    ...
    
    override fun onResume() {
        super.onResume()
        (activity as? HostActivity)?.setNavigation(false)
    }
}

对于较低级别的片段（ads/app/home）：

class LowLevelFragment : Fragment() {
    ...
    
    override fun onResume() {
        super.onResume()
        (activity as? HostActivity)?.setNavigation(true)
    }
}

假设您正确设置了mNavController 和mAppBarConfiguration，这应该可以工作。

Answer 2

我找到了解决办法！

我应该对 Moxy 库使用正确的策略。是的，我没有在主题中提及该库，因为我认为它不会破坏应用程序流程。

接口方法的旧策略类型

StateStrategyType(AddToEndSingleStrategy::class)
interface SettingsView : BaseMvpView {
    fun showManageAdsFragment()
    fun showManageAppUIFragment()
    fun showManageHomeUIFragment()
}

接口方法的新策略类型

StateStrategyType(SkipStrategy::class)
interface SettingsView : BaseMvpView {
    fun showManageAdsFragment()
    fun showManageAppUIFragment()
    fun showManageHomeUIFragment()
}