android工作室错误错误:Connection timed out

Question

我只是在 android studio 中新建了一个项目，并向其中添加了 gcm 模块。
我一直给出这个错误信息

Error:Connection timed out: connect. If you are behind an HTTP proxy, please configure the proxy settings either in IDE or Gradle.      

而且我不使用任何代理。
谁能帮我解决这个问题？

更新
现在重建我的项目后我给出了这个错误

Error:A problem occurred configuring project ':app'.    
 A problem occurred configuring project ':backend'.
Could not resolve all dependencies for configuration ':backend:classpath'.
   Could not resolve com.google.appengine:gradle-appengine-plugin:1.9.18.
    Required by:
        PushStart:backend:unspecified
      Could not resolve com.google.appengine:gradle-appengine-plugin:1.9.18.
      Could not get resource 'https://jcenter.bintray.com/com/google/appengine/gradle-appengine-plugin/1.9.18/gradle-appengine-plugin-1.9.18.pom'.
      Could not GET 'https://jcenter.bintray.com/com/google/appengine/gradle-appengine-plugin/1.9.18/gradle-appengine-plugin-1.9.18.pom'.
      Connection to https://jcenter.bintray.com refused

Answer 1

只需尝试使缓存无效.. 转到文件->使缓存无效/重新启动->选择“无效并重新启动”。