网上教程7.0大多数配置是这样compile 'com.jakewharton:butterknife:7.0.1' ，不知道他们用的Android Studio是多少版本，我用的3.0并没有成功，报错如下：
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 (com.jakewharton:butterknife:7.0.1)
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.
解决办法：加上 annotationProcessor 'com.jakewharton:butterknife:7.0.1'即可解决
