Androidx 遷移方法：
首先把 gradle 版本改爲3.2.0以上，以及 compileSdkVersion 爲28以上
然後 Android Studio 菜單欄 Refactor -> Migrate to AndroidX
如果是新項目，使用AndroidX相關依賴，可以在gradle.properties文件裏添加配置：
android.useAndroidX=true
android.enableJetifier=true
如果你只是想使用AndroidX，但是之前的不遷移，可以這樣配置：
android.useAndroidX=true
android.enableJetifier=false
遷移完成後運行報錯。。。
Conflict with dependency 'androidx.lifecycle:lifecycle-runtime' in project ':app'. Resolved versions for runtime classpath (2.0.0-rc01) and compile classpath (2.0.0) differ. This can lead to runtime crashes. To resolve this issue follow advice at https://developer.android.com/studio/build/gradle-tips#configure-project-wide-properties. Alternatively, you can try to fix the problem by adding this snippet to ...\...\..\..\build.gradle:
根據提示解決：
subprojects {
project.buildDir = "${rootProject.buildDir}/${project.name}"
project.configurations.all {
resolutionStrategy.eachDependency { details ->
if (details.requested.group == 'com.android.support'
&& !details.requested.name.contains('multidex') ) {
details.useVersion "27.1.1"
}else if(details.requested.group == 'androidx.lifecycle')
{
details.useVersion "2.0.0-rc01"
}else if(details.requested.group == 'androidx.versionedparcelable')
{
details.useVersion "1.0.0-rc01"
}else if(details.requested.group == 'androidx.core')
{
details.useVersion "1.0.0-rc01"
}
}
}
}