After Updating Android studio to 3.1.2 , I get "Failed to load AppCompat ActionBar with unknown error. "

Question

I tried looking other similar questions on stackoverflow, they advice us to changw version of "buildToolsVersion" but I dont see word like that in my gradle file.

My Gradle File (PROJECT):-

buildscript {

repositories {
    google()
    jcenter()
}
dependencies {
    classpath 'com.android.tools.build:gradle:3.1.2'


    // NOTE: Do not place your application dependencies here; they belong
    // in the individual module build.gradle files
}
}

allprojects {
repositories {
    google()
    jcenter()
}
}

task clean(type: Delete) {
delete rootProject.buildDir
}

My build.gradle (Module:app): This the my second gradle file

     apply plugin: 'com.android.application'

 android {
 compileSdkVersion 28
 defaultConfig {
    applicationId "com.example.dhruv.testhello"
    minSdkVersion 15
    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-alpha3'
implementation 'com.android.support.constraint:constraint-layout:1.1.1'
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'
 }

Answer 1

I was helped by Hossein Seifi's reply but with a change

implementation 'com.android.support:design:28.0.0-alpha3'

to

implementation 'com.android.support:design:28.0.0-alpha1'

and click File -> Invalidate Caches / Restart

Answer 2

I had the same problem. I searched so much and I finally found that appcompat-v7:28.0.0-alpha3 has some bug with "Design View" part of Android Studio.

So I suggest to change com.android.support:appcompat-v7:28.0.0-alpha3 to com.android.support:appcompat-v7:28.0.0-alpha1 version and then click File -> Invalidate Caches / Restart. Volla everything is OK.

Of course you should have internet access to download com.android.support:appcompat-v7:28.0.0-alpha1