当我在build.gradle(Project：Allo)中同步我的项目时,我看到了这个错误

Failed to find target with hash string ‘android-28’in: C:\Users\hacker\AppData\Local\Android\Sdk

配置：

apply plugin: 'com.google.gms.google-services'
android {
compileSdkVersion 28
defaultConfig {
    applicationId "com.example.android.allo"
    minSdkVersion 19
    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 rc2'
implementation 'com.android.support.constraint:constraint-layout:1.1.0'
implementation 'com.google.firebase:firebase-core:15.0.2'
implementation 'com.google.firebase:firebase-messaging:15.0.2'
implementation 'com.android.support:design:28.0.0 rc2'
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'
}

解决方法:

阅读Set Up the Android P SDK.

android {
compileSdkVersion 'android-P'

defaultConfig {
    targetSdkVersion 'P'
}

For the best development experience with the Android P Preview SDK, we
recommend that you install the latest Android Studio 3.2 canary.

您应按如下方式安装Android P Preview SDK：

>点击工具> SDK Manager.
>在SDK平台选项卡中,选择Android P预览.
>在SDK工具选项卡中,选择Android SDK Build-Tools 28-rc2(或
更高).
>单击“确定”开始安装.