编译错误如下所示：
Duplicate class android.support.v4.app.INotificationSideChannel found in modules classes.jar (androidx.core:core:1.0.0) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.app.INotificationSideChannel$Stub found in modules classes.jar (androidx.core:core:1.0.0) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.app.INotificationSideChannel$Stub$Proxy found in modules classes.jar (androidx.core:core:1.0.0) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.IResultReceiver found in modules classes.jar (androidx.core:core:1.0.0) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.IResultReceiver$Stub found in modules classes.jar (androidx.core:core:1.0.0) 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:1.0.0) 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:1.0.0) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.ResultReceiver$1 found in modules classes.jar (androidx.core:core:1.0.0) and classes.jar (com.android.support:support-compat:27.1.1)
Duplicate class android.support.v4.os.ResultReceiver$MyResultReceiver found in modules classes.jar (androidx.core:core:1.0.0) 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:1.0.0) and classes.jar (com.android.support:support-compat:27.1.1)
在更新了 Android Studio 3.5 版本以后可能会在编译时出现这个问题，由于 3.5 版本之后统一默认为 androidx，这种设置会和早期的 Android 开发工具包产生冲突，例如我遇到的就是上图所示的 v4 和 androidx 中有方法名重复的问题。
所谓的 android.support 是早期的 Android 开发工具包，大部分的控件都是依赖这个工具包，并且由于各种历史因素，已经出现了 android.support.v4、android.support.v7、android.support.v13 等多个版本，每次更新版本都会免不了要替换相关控件的包名。所以为了解决这个麻烦的版本更新问题，现在统一成了 androidx。
解决方法：
找到 gradle.properties 文件，添加如下内容：
android.useAndroidX=true
android.enableJetifier=true