title: cannot resolve symbol and method
body: <p>My android studio version is 2.3.3</p>
  
  <pre><code>    android {
          compileSdkVersion 25
          buildToolsVersion '25.0.0'
          defaultConfig {
              applicationId "com.example.newstest"
              minSdkVersion 15
              targetSdkVersion 25
              versionCode 1
              versionName "1.0"
              testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
          }
  ...
  dependencies {
              compile fileTree(include: ['*.jar'], dir: 'libs')
              androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
                  exclude group: 'com.android.support', module: 'support-annotations'
              })
              compile 'com.android.support:appcompat-v7:25.+'
              compile 'com.android.support.constraint:constraint-layout:1.0.2'
  
              compile 'com.android.support:recyclerview-v7:25.+'
              compile 'com.android.support:support-annotations:+'
              testCompile 'junit:junit:4.12'}
  </code></pre>
  
  <p>I have downloaded SDK platform versions from 4.0 to 8.0, enabled everything in 'SDK Update Sites' panel and installed 'support repositories', 'android sdk build-tools','android sdk platform-tools','android sdk tools','documentation for android sdk' and even'google play services' and selected Android SDK location correctly. I use Android Studio embedded JDK.</p>
  
  <p>But when I want to see the implementation of 'onCreate()' method in Activity.java, some keywords and methods involved are red. And when I move my mouse to it, it shows 'cannot resolve symbol xxx' or 'cannot resolve method xxx'
  I've search this on stack overflow, and some said try 'invalidate and restart'. I did try, and when it restarted, progress 'indexing' appeared, and all the red words in Activity.java turned white. And I could see their declarations at that time. But when 'indexing' disappeared, all the work was done, the red words, which turned white for a few seconds, turned red again and I wasn't able to see their declarations again.</p>
  
  <p>It's not possible for me to open every declaration of the keywords in those a few seconds, it's not just about this onCreate method, I think it's about all the sources when it comes to bottom implementation like this, but I've actually downloaded them. so any solutions for this kind of situation? Thanks very much!</p>