如何解决动态特性模块中数据绑定不起作用,引用绑定的视图时导致空指针异常
我有一个名为 favorite
的 dynamic features module。该模块有安装时交付。在这个模块中,我使用了数据绑定。但是,当我想访问视图的 ID 时,它说该视图为空。
查看我正在使用的 favorite
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,那里有两个具有各自 ID 的视图。然后,我想在我的 favorite
模块片段中引用这些视图。我就是这样做的。
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 binding.fragFavoriteViewPager
引用 ViewPager。在构建期间,没有错误。但是,在运行时,当我尝试导航到此 FavoriteFragment
时,它返回空指针异常错误。该错误告诉我 binding.fragFavoriteViewPager
是一个空对象引用。完整错误如下所示。
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)
我已经为那个 favorite
模块设置了我的 Gradle 文件。
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")
}
为了导航到那个动态特征片段,在我另一个名为 app
的模块中,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's doc regarding dynamic navigation 对导航图进行了更改。然后我删除了与 binding.AnyView
调用相关的所有代码并使用了布局检查器。事实证明,所有的视图都不再有任何 ID。见下图。
为什么 Layout Inspector 中的 ID 消失了?我该怎么做才能在片段文件中使用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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