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我有一个名为favorite. 该模块具有安装时交付。在这个模块中，我使用数据绑定。但是，当我想访问视图的 ID 时，它说该视图为空。

看看favorite我正在使用的模块中的 XML 布局。

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <data />

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="?android:colorBackground">

        <com.google.android.material.tabs.TabLayout
            android:id="@+id/frag_favorite_tab_layout"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:elevation="@dimen/keyline_0"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <androidx.viewpager2.widget.ViewPager2
            android:id="@+id/frag_favorite_view_pager"
            android:layout_width="0dp"
            android:layout_height="0dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@id/frag_favorite_tab_layout" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

如您所见，那里有两个视图，它们具有各自的 ID。然后，我想在我的favorite模块片段中引用这些视图。我是这样做的。

class FavoriteFragment : BaseFragment() {
    private lateinit var binding: FragFavoriteBinding
    private val viewmodel: FavoriteViewModel by viewModel()
    override var bottomNavigationViewVisibility = View.VISIBLE

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        binding = FragFavoriteBinding.inflate(inflater, container, false)
        binding.lifecycleOwner = this
        loadKoinModules(viewModelModule)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        setupViewPager()
        observeNavigationEvent()
    }

    private fun setupViewPager() {
        val viewPagerAdapter =
            FavoriteViewPagerAdapter(
                childFragmentManager,
                viewLifecycleOwner.lifecycle
            )
        // THIS PART OVER HERE v
        binding.fragFavoriteViewPager.adapter = viewPagerAdapter
        TabLayoutMediator(binding.fragFavoriteTabLayout, binding.fragFavoriteViewPager) { tab, position ->
            when (position) {
                0 -> tab.text = getString(ResR.string.movie_toolbar_text)
                1 -> tab.text = getString(ResR.string.show_toolbar_text)
            }
        }.attach()
        binding.fragFavoriteViewPager.registerOnPageChangeCallback(object: ViewPager2.OnPageChangeCallback() {
            override fun onPageScrollStateChanged(state: Int) {
                super.onPageScrollStateChanged(state)
                if (state == ViewPager.SCROLL_STATE_DRAGGING || state == ViewPager.SCROLL_STATE_SETTLING)
                    EspressoIdlingResource.increment()
                else
                    EspressoIdlingResource.decrement()
            }
        })
    }

    private fun observeNavigationEvent() {
        viewmodel.navigateToDetails.observe(viewLifecycleOwner, Observer {
            if (it.first != -1) {
                val action =
                    if (it.second == ListFragment.TYPE_MOVIE) FavoriteFragmentDirections.actionFavoriteFragmentToMovieDetailsFragment2(
                        it.first
                    )
                    else FavoriteFragmentDirections.actionFavoriteFragmentToShowDetailsFragment2(it.first)
                findNavController().navigate(action)
                viewmodel.finishNavigatingToDetails()
            }
        })
    }
}

如上所示，我正在使用 ViewPager 引用binding.fragFavoriteViewPager。在构建期间，没有错误。但是，在运行时，当我尝试导航到 thisFavoriteFragment时，它会返回一个空指针异常错误。该错误告诉我这binding.fragFavoriteViewPager是一个空对象引用。完整的错误可以在下面看到。

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.mobile.moviecatalogue, PID: 13131
    java.lang.NullPointerException: binding.fragFavoriteViewPager must not be null
        at com.mobile.favorite.ui.FavoriteFragment.setupViewPager(FavoriteFragment.kt:50)
        at com.mobile.favorite.ui.FavoriteFragment.onViewCreated(FavoriteFragment.kt:40)
        at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:332)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1199)
        at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2236)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2009)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1965)
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1861)
        at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.mobile.moviecatalogue, PID: 13131
    java.lang.NullPointerException: binding.fragFavoriteViewPager must not be null
        at com.mobile.favorite.ui.FavoriteFragment.setupViewPager(FavoriteFragment.kt:50)
        at com.mobile.favorite.ui.FavoriteFragment.onViewCreated(FavoriteFragment.kt:40)
        at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:332)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1199)
        at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2236)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2009)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1965)
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1861)
        at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

我已经为该favorite模块设置了我的 Gradle 文件，就像这样。

plugins {
    id 'com.android.dynamic-feature'
    id 'kotlin-android'
    id 'kotlin-kapt'
}

apply from: '../shared_dependencies.gradle'

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.2"

    defaultConfig {
        applicationId "com.mobile.favorite"
        minSdkVersion 27
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    buildFeatures {
        dataBinding true
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
}

dependencies {
    implementation project(":core")
    implementation project(":app")
    implementation project(":res")
}

要导航到该动态功能片段，在我的另一个名为 的模块中app，我有这个导航图。

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main_navigation"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    app:startDestination="@id/movieFragment">

    ...
    <fragment
        app:moduleName="favorite"
        android:id="@+id/favoriteFragment"
        android:name="com.mobile.favorite.ui.FavoriteFragment"
        android:label="@string/favorite_toolbar_text"
        tools:layout="@layout/frag_favorite">
        <action
            android:id="@+id/action_favoriteFragment_to_movieDetailsFragment2"
            app:destination="@id/movieDetailsFragment"
            app:enterAnim="@anim/nav_default_enter_anim"
            app:exitAnim="@anim/nav_default_exit_anim"
            app:popEnterAnim="@anim/nav_default_pop_enter_anim"
            app:popExitAnim="@anim/nav_default_pop_exit_anim" />
        <action
            android:id="@+id/action_favoriteFragment_to_showDetailsFragment2"
            app:destination="@id/showDetailsFragment"
            app:enterAnim="@anim/nav_default_enter_anim"
            app:exitAnim="@anim/nav_default_exit_anim"
            app:popEnterAnim="@anim/nav_default_pop_enter_anim"
            app:popExitAnim="@anim/nav_default_pop_exit_anim" />
    </fragment>
    ...
    <action
        android:id="@+id/action_global_favoriteFragment"
        app:destination="@id/favoriteFragment"
        app:enterAnim="@anim/nav_default_enter_anim"
        app:exitAnim="@anim/nav_default_exit_anim"
        app:popEnterAnim="@anim/nav_default_pop_enter_anim"
        app:popExitAnim="@anim/nav_default_pop_exit_anim" />
</navigation>

我根据Android 的关于动态导航的文档对导航图进行了更改。然后我删除了与调用binding.AnyView和使用 Layout Inspector 相关的所有代码。事实证明，所有视图都不再具有任何 ID。请看下面这张图片。

在此处输入图像描述

为什么 ID 在 Layout Inspector 中消失了？我该怎么做才能使用片段文件中的数据绑定来引用视图？

编辑

使用binding.root.findViewById，我可以访问视图。这很奇怪。

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