I am new to Android Studio and I don&#39;t get why my toolbar isn&#39;t shown as described by https://developer.android.com/training/appbar/setting-up
I know there are already some other questions like mine on stackoverflow but they don&#39;t work at my project. Therefore I would be very thankful for fixing this issue. Screenshot:

[![Screenshot][1]][1]



    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
=======

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
    &lt;android.support.v7.widget.Toolbar xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
        android:layout_width=&quot;match_parent&quot;
        android:layout_height=&quot;match_parent&quot;
        android:background=&quot;@color/colorPrimaryDark&quot;&gt;
    
    &lt;/android.support.v7.widget.Toolbar&gt;

build.gradle (app level)
=======

    apply plugin: &#39;com.android.application&#39;
    android {
		compileSdkVersion 28
		defaultConfig {
			applicationId &quot;com.example.david.gamebase&quot;
			minSdkVersion 21
			targetSdkVersion 28
			versionCode 1
			versionName &quot;1.0&quot;
			testInstrumentationRunner &quot;android.support.test.runner.AndroidJUnitRunner&quot;
		}
		buildTypes {
			release {
				minifyEnabled false
				proguardFiles getDefaultProguardFile(&#39;proguard-android.txt&#39;), &#39;proguard-rules.pro&#39;
			}
		}
	}

    dependencies {
		implementation fileTree(dir: &#39;libs&#39;, include: [&#39;*.jar&#39;])
		implementation &#39;com.android.support:appcompat-v7:28.0.0-rc01&#39;
		implementation &#39;com.android.support.constraint:constraint-layout:1.1.2&#39;
		implementation &#39;com.google.firebase:firebase-auth:11.6.0&#39;
		testImplementation &#39;junit:junit:4.12&#39;
		androidTestImplementation &#39;com.android.support.test:runner:1.0.2&#39;
		androidTestImplementation &#39;com.android.support.test.espresso:espresso-core:3.0.2&#39;
	}

    apply plugin: &#39;com.google.gms.google-services&#39;


style.xml:
---------

 

       &lt;resources&gt;
    
        &lt;!-- Base application theme. --&gt;
        &lt;style name=&quot;AppTheme&quot; parent=&quot;Base.Theme.AppCompat.Light.DarkActionBar&quot;&gt;
            &lt;!-- Customize your theme here. --&gt;
            &lt;item name=&quot;colorPrimary&quot;&gt;@color/colorPrimary&lt;/item&gt;
            &lt;item name=&quot;colorPrimaryDark&quot;&gt;@color/colorPrimaryDark&lt;/item&gt;
            &lt;item name=&quot;colorAccent&quot;&gt;@color/colorAccent&lt;/item&gt;
        &lt;/style&gt;
    
    &lt;/resources&gt;
    
    ## toolbar.xml ##
    
        &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
    &lt;android.support.v7.widget.Toolbar xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
        android:layout_width=&quot;match_parent&quot;
        android:layout_height=&quot;match_parent&quot;
        android:background=&quot;@color/colorPrimaryDark&quot;&gt;
    
    &lt;/android.support.v7.widget.Toolbar&gt;


  [1]: https://i.stack.imgur.com/kpx3o.png

All Unhandled Solutions on Gang of Coders

Total of 1 Unhandled Solutions

android.view.View$OnUnhandledKeyEventListener