android 9.0以后，谷歌建议使用这个库，替换过程中，与原有的库出现错误如下

Duplicate class android.support.v4.app.INotificationSideChannel found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.app.INotificationSideChannel$Stub found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.app.INotificationSideChannel$Stub$Proxy found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.IResultReceiver found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.IResultReceiver$Stub found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.IResultReceiver$Stub$Proxy found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.ResultReceiver found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.ResultReceiver$1 found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.ResultReceiver$MyResultReceiver found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.ResultReceiver$MyRunnable found in modules classes.jar (androidx.core:core:1.1.0-beta01) and classes.jar (com.android.support:support-compat:27.1.1)

Go to the documentation to learn how to Fix dependency resolution errors.

需要显示指定有限使用androidx，在 gradle.properties 里面进行配置如下

# When configured, Gradle will run in incubating parallel mode.
# This option should only be used with decoupled projects. More details, visit
# http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
# org.gradle.parallel=true
# AndroidX package structure to make it clearer which packages are bundled with the
# Android operating system, and which are packaged with your app's APK
# https://developer.android.com/topic/libraries/support-library/androidx-rn
android.useAndroidX=true
# Automatically convert third-party libraries to use AndroidX
android.enableJetifier=true
gradle.properties

androidx对原有的一些组件修改，还是不够完善，有bug，谨慎替换！！！
androidx使用交流邮箱 liugstick@163.com ，欢迎骚扰！！！