Я новичок в Android Studio, и я не понимаю, почему моя панель инструментов не отображается, как описано https://developer.android.com/training/appbar/setting-up Я знаю, что уже есть некоторые другие вопросы, подобные моему, по stackoverflow, но они не работают в моем проекте. Поэтому я был бы очень благодарен за исправление этой проблемы. Скриншот:

java.lang.ClassNotFoundException: android.view.View$OnUnhandledKeyEventListener
at org.jetbrains.android.uipreview.ModuleClassLoader.load(ModuleClassLoader.java:180)
at com.android.tools.idea.rendering.RenderClassLoader.findClass(RenderClassLoader.java:61)
at org.jetbrains.android.uipreview.ModuleClassLoader.findClass(ModuleClassLoader.java:118)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.jetbrains.android.uipreview.ModuleClassLoader.loadClass(ModuleClassLoader.java:213)
at android.support.v7.widget.ViewUtils.isLayoutRtl(ViewUtils.java:58)
at android.support.v7.widget.Toolbar.onMeasure_Original(Toolbar.java:1578)
at android.support.v7.widget.Toolbar.onMeasure(Toolbar.java)
at android.view.View.measure_Original(View.java:22071)
at android.view.View_Delegate.measure(View_Delegate.java:80)
at android.view.View.measure(View.java:22035)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6602)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.view.View.measure_Original(View.java:22071)
at android.view.View_Delegate.measure(View_Delegate.java:80)
at android.view.View.measure(View.java:22035)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
at android.view.View.measure_Original(View.java:22071)
at android.view.View_Delegate.measure(View_Delegate.java:80)
at android.view.View.measure(View.java:22035)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.measureView(RenderSessionImpl.java:590)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:343)
at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:384)
at com.android.tools.idea.layoutlib.LayoutLibrary.createSession(LayoutLibrary.java:193)
at com.android.tools.idea.rendering.RenderTask.createRenderSession(RenderTask.java:544)
at com.android.tools.idea.rendering.RenderTask.lambda$inflate$3(RenderTask.java:678)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

toolbar.xml

<?xml version = "1.0" encoding = "utf-8"?>
<android.support.v7.widget.Toolbar xmlns:android = "http://schemas.android.com/apk/res/android"
    android:layout_width = "match_parent"
    android:layout_height = "match_parent"
    android:background = "@color/colorPrimaryDark">

</android.support.v7.widget.Toolbar>

build.gradle (уровень приложения)

apply plugin: 'com.android.application'
android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.example.david.gamebase"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:28.0.0-rc01'
    implementation 'com.android.support.constraint:constraint-layout:1.1.2'
    implementation 'com.google.firebase:firebase-auth:11.6.0'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

apply plugin: 'com.google.gms.google-services'

style.xml:

   <resources>

    <!-- Base application theme. -->
    <style name = "AppTheme" parent = "Base.Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name = "colorPrimary">@color/colorPrimary</item>
        <item name = "colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name = "colorAccent">@color/colorAccent</item>
    </style>

</resources>

## toolbar.xml ##

    <?xml version = "1.0" encoding = "utf-8"?>
<android.support.v7.widget.Toolbar xmlns:android = "http://schemas.android.com/apk/res/android"
    android:layout_width = "match_parent"
    android:layout_height = "match_parent"
    android:background = "@color/colorPrimaryDark">

</android.support.v7.widget.Toolbar>