在使用butter knife报错Annotation processors must be explicitly declared now.

错误如下：

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.

解决如下：

在build.gradle下的android中的defaultConfig标签下加上

    javaCompileOptions {
            annotationProcessorOptions {
                includeCompileClasspath = true    //加上这行即可
            }
        }

（完，发现不再报错）