Cannot resolve symbol 'AppCompatActivity' , Cannot resolve symbol 'R', Could not download support-co

Ask Question

up vote 1 down vote favorite

I installed Android Studio 2.1.3, and successfully created a new project (just call it ProA),it runs well in AVD. That time I had just only downloaded the sdk platform android-24 . I created that project with the Minimum SDK API 14. Acutally , I didn't download android-14 that time. Then latter I downloaded android-14, androdi-15,android-21,android-23, tried to create a new project (call it ProB), but many errors occurred there. The  MainActivity 's superclass is  AppCompatActivity  , but the error is  Cannot solve symbol 'AppCompatActivity' . There is a red line under the  @Override  tag over the  onCreate()  method,saying that  Method does not override method from its superclass In  onCreate()  method ,the  setContentView(R.layout.activity_main)  code snippet shows  Cannot resolve symbol 'R' . The Messages window has a error message saying A problem occurred configuring project ':app'. Could not download support-compat.aar(com.android.support:-compat:24.2.0): No cached version available for offline mode the overall picture is like this: the overall error image(click to see) the content of app\src\build.gradle: apply plugin: 'com.android.application' android { compileSdkVersion 24 buildToolsVersion "24.0.1" defaultConfig { applicationId "com.example.zhangsir.aftervpn" minSdkVersion 14 targetSdkVersion 24 versionCode 1 versionName "1.0" } buildTypes { release { minifyEnabled false proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro' } } } dependencies { compile fileTree(dir: 'libs', include: ['*.jar']) testCompile 'junit:junit:4.12' compile 'com.android.support:appcompat-v7:24.2.0' } the content of gradle\build.gradle: // Top-level build file where you can add configuration options common to all sub-projects/modules. buildscript { repositories { jcenter() } dependencies { classpath 'com.android.tools.build:gradle:2.1.3' // NOTE: Do not place your application dependencies here; they belong // in the individual module build.gradle files } } allprojects { repositories { jcenter() } } task clean(type: Delete) { delete rootProject.buildDir } the screenshot of the standalone sdk manager (click to see) modified at 2016 Aug,27 I have downloaded all the Android SDK Build-tools: What can I do to solve this problem?