java.lang.IllegalStateException：findViewById（R.id.adView）不能为空

Question

我正在尝试在第一个Android项目中配置AdMod。当我尝试运行该应用程序时，findViewByID始终返回null。现在我知道为什么会这样了，我从Google那里得到了相同的代码，有人可以帮我吗？

这里是活动代码：

package com.alotaibi.alphabetapp

import android.media.MediaPlayer
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.google.android.gms.ads.AdRequest
import com.google.android.gms.ads.AdView
import com.google.android.gms.ads.MobileAds
import kotlinx.android.synthetic.main.activity_english_menu.*

var engMenu:MediaPlayer?= MediaPlayer()
lateinit var mAdView_engMen: AdView

class english_menu : AppCompatActivity() {
var t=iTools(this)

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


    MobileAds.initialize(this) {}
    mAdView_engMen = findViewById(R.id.adView)
    val adRequest = AdRequest.Builder().build()
    mAdView_engMen.loadAd(adRequest)


    engMenu = MediaPlayer.create(this,R.raw.starteng)
    engMenu!!.setOnCompletionListener { mp ->
        mp.reset()
        mp.release()
        engMenu = null
    }
    engMenu?.start()

    abc.setOnClickListener {
        t.openActivity(upperCase::class)
    }
    quiz.setOnClickListener {
        t.openActivity(engGame::class)
    }
    pho.setOnClickListener {
        t.openActivity(yaraabb::class)
    }
    pra.setOnClickListener {
        t.openActivity(practiceEng::class)
    }
}


override fun onPause() {
    super.onPause()
    if(engMenu!=null) {
        engMenu?.release()
    }
}
}

XML文件（在res \ layout下）具有以下内容：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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="@drawable/aa"
android:orientation="vertical"
tools:context=".english_menu">

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_weight="1">

    <ImageView
        android:id="@+id/abc"
        android:layout_width="200dp"
        android:layout_height="250dp"
        android:layout_marginTop="20dp"
        android:layout_weight="1"
        app:srcCompat="@drawable/eng" />

    <ImageView
        android:id="@+id/pho"
        android:layout_width="200dp"
        android:layout_height="250dp"
        android:layout_marginTop="20dp"
        android:layout_weight="1"
        app:srcCompat="@drawable/phonics" />

    <ImageView
        android:id="@+id/pra"
        android:layout_width="200dp"
        android:layout_height="250dp"
        android:layout_marginTop="20dp"
        android:layout_weight="1"
        app:srcCompat="@drawable/practice" />

    <ImageView
        android:id="@+id/quiz"
        android:layout_width="200dp"
        android:layout_height="250dp"
        android:layout_marginTop="20dp"
        android:layout_weight="1"
        app:srcCompat="@drawable/quiz" />
</LinearLayout>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

    <com.google.android.gms.ads.AdView
        android:id="@+id/adView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_gravity="bottom|center_horizontal"
        app:adSize="BANNER"
        app:adUnitId="ca-app-pub-3940256099942544/6300978111"/>

</LinearLayout>

而且我不知道该如何解决这个问题，请helppp meeeee

Answer 1

您需要将所有内容放入相同的布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    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="@drawable/aa"
    android:orientation="vertical"
    tools:context=".english_menu">

    <ImageView
        android:id="@+id/abc"
        android:layout_width="200dp"
        android:layout_height="250dp"
        android:layout_marginTop="20dp"
        android:layout_weight="1"
        app:srcCompat="@drawable/eng" />

    <ImageView
        android:id="@+id/pho"
        android:layout_width="200dp"
        android:layout_height="250dp"
        android:layout_marginTop="20dp"
        android:layout_weight="1"
        app:srcCompat="@drawable/phonics" />

    <ImageView
        android:id="@+id/pra"
        android:layout_width="200dp"
        android:layout_height="250dp"
        android:layout_marginTop="20dp"
        android:layout_weight="1"
        app:srcCompat="@drawable/practice" />

    <ImageView
        android:id="@+id/quiz"
        android:layout_width="200dp"
        android:layout_height="250dp"
        android:layout_marginTop="20dp"
        android:layout_weight="1"
        app:srcCompat="@drawable/quiz" />


    <com.google.android.gms.ads.AdView
        android:id="@+id/adView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_gravity="bottom|center_horizontal"
        app:adSize="BANNER"
        app:adUnitId="ca-app-pub-3940256099942544/6300978111"
        android:layout_weight="1"/>

</LinearLayout>