我是Android Studio的新手,我不知道为什么我的工具栏没有按照https://developer.android.com/training/appbar/setting-up所描述的那样显示 我知道已经有一些像我这样的问题了stackoverflow但它们不适用于我的项目.因此,我非常感谢解决这个问题.截图:

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"> …

任何人都可以帮助为什么会出错？

一切都很好,突然间出现了这个错误.

我用Google搜索但无法得到任何东西!请帮忙

错误:(7,41)找不到与给定名称匹配的资源(在'dialogCornerRadius'中,值为'？android:attr/dialogCornerRadius').

apply plugin: 'com.android.application'

//Add these lines
def Base_URL = '"' + WEBServiceBaseURL + '"' ?: '"Define BASE URL"';
def SMS_Base_URL = '"' + WEBServiceBaseSMSURL + '"' ?: '"Define SMS BASE URL"';

android.buildTypes.each { type ->
    type.buildConfigField 'String', 'Base_URL', WEBServiceBaseURL
    type.buildConfigField 'String', 'SMS_Base_URL', WEBServiceBaseSMSURL
}

android {
    compileSdkVersion 26
    buildToolsVersion "26.0.1"
    defaultConfig {
        applicationId "com.bla.bla"
        minSdkVersion 19
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        multiDexEnabled  true
    }
    buildTypes {
        release {
            minifyEnabled true
            shrinkResources true
            proguardFiles …

以下是我得到的错误

C:\Users\Dell\.gradle\caches\transforms-1\files-1.1\appcompat-v7-28.0.0-alpha1.aar\51cd62c84e9404bd66ab4daf252c48a1\res\values-v28\values-v28.xml
Error:(9, 5) error: resource android:attr/dialogCornerRadius not found.
C:\Users\Dell\.gradle\caches\transforms-1\files-1.1\appcompat-v7-28.0.0-alpha1.aar\51cd62c84e9404bd66ab4daf252c48a1\res\values\values.xml
Error:(252, 5) error: resource android:attr/fontVariationSettings not found.
Error:(252, 5) error: resource android:attr/ttcIndex not found.
E:\20thJune2017_7PM\trunk\app\build\intermediates\incremental\mergeDebugResources\merged.dir\values-v28\values-v28.xml
Error:(11) error: resource android:attr/dialogCornerRadius not found.
Error:(7) resource android:attr/dialogCornerRadius not found.
Error:(11) resource android:attr/dialogCornerRadius not found.
E:\20thJune2017_7PM\trunk\app\build\intermediates\incremental\mergeDebugResources\merged.dir\values\values.xml
Error:(486) resource android:attr/fontVariationSettings not found.
Error:(486) resource android:attr/ttcIndex not found.
Error:failed linking references.
Error:java.util.concurrent.ExecutionException: java.util.concurrent.ExecutionException: com.android.tools.aapt2.Aapt2Exception: AAPT2 error: check logs for details
Error:java.util.concurrent.ExecutionException: com.android.tools.aapt2.Aapt2Exception: AAPT2 error: check logs for details
Error:com.android.tools.aapt2.Aapt2Exception: AAPT2 error: check logs for details
Error:Execution …