AndroidStudio3.0 注解报错Annotation processors must be explicitly declared now. The following dependencies on the compile classpath are found to contain annotation processor.

 把Androidstudio2.2的项目放到3.0里面去了，然后开始报错了。

体验最新版AndroidStudio3.0 Canary 8的时候，发现之前项目的butter knife报错，用到注解的应该都会报错
Error:Execution failed for task ':app:javaPreCompileDebug'.
> Annotation processors must be explicitly declared now.  The following dependencies on the compile classpath are found to contain annotation processor.  Please add them to the annotationProcessor configuration.
    - butterknife-7.0.1.jar
  Alternatively, set android.defaultConfig.javaCompileOptions.annotationProcessorOptions.includeCompileClasspath = true to continue with previous behavior.  Note that this option is deprecated and will be removed in the future.
  See https://developer.android.com/r/tools/annotation-processor-error-message.html for more details.

在app的build中
android {
    ...
    defaultConfig {
        ...
        //添加如下配置就OK了
        javaCompileOptions { annotationProcessorOptions { includeCompileClasspath = true } }
    }
    ...
}

记住一点：改完了之后，别忘了继续sync Now.而不是：刷新按钮，别忘了

参考：AndroidStudio3.0 注解报错Annotation processors must be explicitly declared now. The following dependencies on the compile classpath are found to contain annotation processor.