Kotlin应用程序，单击按钮以打开新活动-> IllegalStateException：findViewById不能为null

我正在使用“学习Kotlin进行Android开发”这个博克游戏，并已进入第9章。我现在有2个活动。该MainActivity具有在与信息按钮顶部的menue酒吧。此按钮应打开StatisticsActiv。

该MainActivity.kt使用调用函数onOptionsItemSelected应点击信息按钮在菜单栏等功能“openStatistics”，这会写在意向活动后调用。但这并没有发生...相反，我得到了异常：java.lang.IllegalStateException：findViewById（statisticsContainer）不能为null（完整的异常如下所示）

AndroidManifext.xml

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".StatisticsActivity" />
    <activity
        android:name=".MainActivity"
        android:theme="@style/AppTheme.NoActionBar">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <meta-data
        android:name="android.support.PARENT_ACTIVITY"
        android:value=".MainActivity" />
</application>

MainActivity.kt

class MainActivity : AppCompatActivity() {
    val rnd: RandomNumberGenerator = StdRandom()
    // or ... = RandomRandom()
    var started = false
    var number = 0
    var tries = 0
    var gameUser = GameUser(
        lastName = "Doe",
        firstName = "John",
        userName = "jdoe",
        birthday = "1900-01-01",
        registrationNumber = 0,
        userRank = 0.0
    )

    override
    fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(toolbar)

        fetchSavedInstanceData(savedInstanceState)
        doGuess.setEnabled(started)
    }

    override
    fun onCreateOptionsMenu(menu: Menu): Boolean {
        val inflater: MenuInflater = menuInflater
        inflater.inflate(R.menu.menu_options, menu)
        return true
    }

    override
    fun onOptionsItemSelected(item: MenuItem): Boolean {
        val statisticsContainer = R.id.statisticsContainer
        val displayTextView: TextView = findViewById(statisticsContainer)
        openStatistics()
        displayTextView.text = "TEST"
        return super.onOptionsItemSelected(item)
    }

    private fun openStatistics() {
        val intent = Intent(this, StatisticsActivity::class.java)
        startActivity(intent)
    }

    override
    fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)
        putInstanceData(outState)
    }

}

我以为，如果我单击菜单栏上的信息按钮，则应使用功能“ onOptionsItemSelected”，因此应使用功能“ openStatistics”将意图写入活动。

menue_options.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/statistics"
        android:icon="@android:drawable/ic_menu_info_details"
        android:title="@string/statistics.menu_title"
        app:showAsAction="ifRoom" />
</menu>

StatisticsActivity.kt onCreate函数

override
    fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_statistics)

        restoreData(savedInstanceState)
        showData(Statistics.getStatistics())
    }

统计信息容器布局：activity_statistics.xml

<?xml version="1.0" encoding="utf-8"?>
<TextView
    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/statisticsContainer"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:layout_height="match_parent"
    tools:context=".StatisticsActivity">
</TextView>

单击信息按钮后发生异常

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: kotlinforandroid.book.numberguess, PID: 5201
    java.lang.IllegalStateException: findViewById(statisticsContainer) must not be null
        at kotlinforandroid.book.numberguess.MainActivity.onOptionsItemSelected(MainActivity.kt:55)
        at android.app.Activity.onMenuItemSelected(Activity.java:3450)
        at androidx.fragment.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:384)
        at androidx.appcompat.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:219)
        at androidx.appcompat.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:109)
        at androidx.appcompat.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:109)
        at androidx.appcompat.app.ToolbarActionBar$2.onMenuItemClick(ToolbarActionBar.java:64)
        at androidx.appcompat.widget.Toolbar$1.onMenuItemClick(Toolbar.java:207)
        at androidx.appcompat.widget.ActionMenuView$MenuBuilderCallback.onMenuItemSelected(ActionMenuView.java:781)
        at androidx.appcompat.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:840)
        at androidx.appcompat.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:158)
        at androidx.appcompat.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:991)
        at androidx.appcompat.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:981)
        at androidx.appcompat.widget.ActionMenuView.invokeItem(ActionMenuView.java:625)
        at androidx.appcompat.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:151)
        at android.view.View.performClick(View.java:6294)
        at android.view.View$PerformClick.run(View.java:24770)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)