带有（架构导航组件）和 BottomNavigationView 的启动画面

Question

我试图为包含 BottomNavigationView 和三个片段的我的应用程序实现闪屏，我使用了最著名的方法，如 answer 来做到这一点而无需创建新的 activity 或片段，但问题在直接启动启动画面后出现，它得到 "RuntimeException and NullPointerException"

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.mml.foody, PID: 6868
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mml.foody/com.mml.foody.ui.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
        at androidx.navigation.ui.ActionBarOnDestinationChangedListener.setTitle(ActionBarOnDestinationChangedListener.java:48)
        at androidx.navigation.ui.AbstractAppBarOnDestinationChangedListener.onDestinationChanged(AbstractAppBarOnDestinationChangedListener.java:103)
        at androidx.navigation.NavController.addOnDestinationChangedListener(NavController.java:233)
        at androidx.navigation.ui.NavigationUI.setupActionBarWithNavController(NavigationUI.java:237)
        at androidx.navigation.ui.ActivityKt.setupActionBarWithNavController(Activity.kt:74)
        at com.mml.foody.ui.MainActivity.onCreate(MainActivity.kt:39)
        at android.app.Activity.performCreate(Activity.java:8000)
        at android.app.Activity.performCreate(Activity.java:7984)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:223) 
        at android.app.ActivityThread.main(ActivityThread.java:7656) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 
I/Process: Sending signal. PID: 6868 SIG: 9

风格

<style name="SplashScreenStyle" parent="Theme.MaterialComponents.DayNight.NoActionBar">
        <item name="android:windowBackground">@drawable/splash_screen</item>
    </style>

AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.mml.foody">

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

    <application
        android:name=".MyApplication"
        android:allowBackup="true"
        android:fullBackupContent="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/SplashScreenStyle"
        android:usesCleartextTraffic="true">
        <activity
            android:name=".ui.DetailsActivity"
            android:label="Details"
            android:theme="@style/DetailsActivityStyle">

        </activity>
        <activity android:name=".ui.MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <meta-data
            android:name="preloaded_fonts"
            android:resource="@array/preloaded_fonts" />
    </application>

</manifest>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<layout 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">

    <data>

    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/lightGray"
        android:orientation="vertical"
        tools:context=".ui.MainActivity">


        <androidx.fragment.app.FragmentContainerView
            android:id="@+id/nav_host_fragment_container"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="2"
            app:defaultNavHost="true"
            app:navGraph="@navigation/nav_graph" />

        <com.google.android.material.bottomnavigation.BottomNavigationView
            android:id="@+id/bottomNavigationView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:menu="@menu/bottom_nav_menu" />

    </LinearLayout>
</layout>

主要活动class

class MainActivity : AppCompatActivity() {

    private lateinit var binding:ActivityMainBinding
    private lateinit var navHostFragment: NavHostFragment
    private lateinit var navController: NavController

    override fun onCreate(savedInstanceState: Bundle?) {
        setTheme(R.style.SplashScreenStyle)
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this, R.layout.activity_main)
        setContentView(binding.root)


        navHostFragment =
            supportFragmentManager.findFragmentById(R.id.nav_host_fragment_container) as NavHostFragment

        navController = navHostFragment.navController

        val appBarConfiguration = AppBarConfiguration(
            setOf(R.id.recipesFragment, R.id.favoriteRecipesFragment, R.id.foodJokeFragment)
        )

        binding.bottomNavigationView.setupWithNavController(navController)
        setupActionBarWithNavController(navController,appBarConfiguration)



    }

    override fun onSupportNavigateUp(): Boolean {
        return navController.navigateUp() ||  super.onSupportNavigateUp()
    }
}

在谷歌搜索此异常后，我看到了这个并且我意识到这个错误是因为我在初始屏幕中使用了 NoActionBar 并且还使用了这个导航组件 setupActionBarWithNavController(navController,appBarConfiguration) 但是我有这个应用程序的旧版本，具有相同的结构和代码，除了它与 plugin: 'kotlin-android-extensions' 一起工作的一件事之外，所有的东西都一样，但我在 main_activity.xml 中使用了数据绑定并且它工作正常，所以我错过了什么或者如何在不创建新的 activity/fragmet 的情况下解决这个问题？

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/lightGray"
    tools:context=".ui.MainActivity">

    <fragment
        android:id="@+id/navHostFragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@+id/bottomNavigationView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/my_nav" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottomNavigationView"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:menu="@menu/bottom_nav_menu"/>

</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

尝试将 android:theme="@style/SplashScreenStyle" 从 application 移动到

<activity android:name=".ui.MainActivity"
    android:theme="@style/SplashScreenStyle">

并在 onCreateView 中设置 AppTheme 因为看起来你正在使用

setTheme(R.style.SplashScreenStyle)

在你的MainActivity.kt

Refer my code

Answer 2

问题出现在这里：setupActionBarWithNavController(navController,appBarConfiguration)。您正在设置一个不存在的 ActionBar，它会导致 NullPointerException。有关更多信息，请参阅官方文档：Navigation Action Bar, Support Action Bar

解决方案：（选择一个）
1/ 如果你不需要 ActionBar 删除这一行：
setupActionBarWithNavController(navController,appBarConfiguration) 在你的 MainActivity 的 onCreate(...) 方法

2/ else 使用 activity 作为初始屏幕并为其余活动创建样式。

<style name="ActivitiesScreenStyle" parent="Theme.MaterialComponents.DayNight">
    <item name="android:windowBackground">@drawable/splash_screen</item>
</style>

在您的 android 清单中：

<application
    ...
    android:theme="@style/ActivitiesScreenStyle"
    ...
    <activity android:name=".ui.YourSplashScreenActivity"
        android:theme="@style/SplashScreenStyle">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

这意味着您的 片段导航 发生在另一个 activity 而不是 YourSplashScreenActivity 上，否则您将再次遇到同样的错误。
伙计干杯！

Answer 3

如果您想要一个包含操作栏或底部导航视图的启动画面，您应该单独创建一个 activity 或片段，我更喜欢用片段来做，因为它轻巧且性能最佳比 activity

像这样创建一个飞溅片段

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/splash_screen"
    tools:context=".ui.fragments.SplashScreenFragment">
</FrameLayout>

在 navGraph 中将 SplashFragment 中的操作添加到您的主页 frgament

<fragment
        android:id="@+id/splashScreenFragment"
        android:name="com.mml.foody.ui.fragments.SplashScreenFragment"
        tools:layout="@layout/fragment_splash_screen">
        <action
            android:id="@+id/action_splashScreenFragment_to_yourHomeFragment"
            app:destination="@id/yourHomeFragment"
            app:launchSingleTop="true"
            app:popUpTo="@id/splashScreenFragment"
            app:popUpToInclusive="true" />
    </fragment>

有了这三个属性，当点击后退按钮时，应用程序会退出而不是返回到启动片段

app:launchSingleTop="true"
app:popUpTo="@id/splashScreenFragment"
app:popUpToInclusive="true" />

将此代码添加到 SplashFragment class 以仅在片段中隐藏操作栏

 override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment

        (activity as AppCompatActivity?)!!.supportActionBar?.hide()
        return inflater.inflate(R.layout.fragment_splash_screen, container, false)


    }

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

        lifecycleScope.launchWhenCreated {
            goToRecipesFragment()
        }

    }



    override fun onDestroyView() {
        super.onDestroyView()
        (activity as AppCompatActivity?)!!.supportActionBar!!.show()
    }

    private suspend fun goToRecipesFragment() {
        delay(3000)
        findNavController()
            .navigate(SplashScreenFragmentDirections.actionSplashScreenFragmentToRecipesFragment())
    }
}

最后隐藏 bottomNavigationView 将此方法添加到 MainActivity

  navController.addOnDestinationChangedListener { _, destination, _ ->
            if(destination.id == R.id.splashScreenFragment) {

                binding.bottomNavigationView.visibility = View.GONE
            } else {

                binding.bottomNavigationView.visibility = View.VISIBLE
            }
        }

带有（架构导航组件）和 BottomNavigationView 的启动画面

Splash screen with (Architecture Navigation Components) and BottomNavigationView

android

splash-screen

android-theme

kotlin

android-databinding