一 AndroidX简述
AndroidX 是 Android 团队用于在 Jetpack 中开发、测试、打包和发布库以及对其进行版本控制的开源项目。
AndroidX 对原始 Android 支持库进行了重大改进。与支持库一样，AndroidX 与 Android 操作系统分开提供，并与各个 Android 版本向后兼容。AndroidX 完全取代了支持库，不仅提供同等的功能，而且提供了新的库。此外，AndroidX 还包括以下功能：
AndroidX 中的所有软件包都使用一致的命名空间，以字符串
androidx开头。支持库软件包已映射到对应的androidx.*软件包。有关所有旧类到新类以及旧编译工件到新编译工件的完整映射，请参阅软件包重构页面。与支持库不同，AndroidX 软件包会单独维护和更新。
androidx软件包使用严格的语义版本控制，从版本 1.0.0 开始。您可以单独更新项目中的 AndroidX 库。所有新支持库的开发工作都将在 AndroidX 库中进行。这包括维护原始支持库工件和引入新的 Jetpack 组件。
二、使用方式：
如果要在新项目中使用 AndroidX，则需要将编译 SDK 设置为 Android 9.0（API 级别 28）或更高版本，并在 gradle.properties 文件中将以下两个 Android Gradle 插件标记设置为 true。
-
android.useAndroidX：如果设置为true，Android 插件会使用相应的 AndroidX 库，而非支持库。如果未指定，则该标记默认为false。 -
android.enableJetifier：如果设置为true，Android 插件会重写其二进制文件，自动迁移现有的第三方库以使用 AndroidX。如果未指定，则该标记默认为false。
针对现有项目，在Android Stuido 打开你需要调整为AndroidX的项目。
1、 在工具栏上选择 Refactor -> Migrate to Androidx
2、在module的build.gradle中把 support就替换对应的androidX包
具体请参阅迁移到 AndroidX。
support与androidX对应关系
| Old build artifact | AndroidX build artifact |
|---|---|
| android.arch.core:common | androidx.arch.core:core-common:2.0.0-rc01 |
| android.arch.core:core | androidx.arch.core:core:2.0.0-rc01 |
| android.arch.core:core-testing | androidx.arch.core:core-testing:2.0.0-rc01 |
| android.arch.core:runtime | androidx.arch.core:core-runtime:2.0.0-rc01 |
| android.arch.lifecycle:common | androidx.lifecycle:lifecycle-common:2.0.0-rc01 |
| android.arch.lifecycle:common-java8 | androidx.lifecycle:lifecycle-common-java8:2.0.0-rc01 |
| android.arch.lifecycle:compiler | androidx.lifecycle:lifecycle-compiler:2.0.0-rc01 |
| android.arch.lifecycle:extensions | androidx.lifecycle:lifecycle-extensions:2.0.0-rc01 |
| android.arch.lifecycle:livedata | androidx.lifecycle:lifecycle-livedata:2.0.0-rc01 |
| android.arch.lifecycle:livedata-core | androidx.lifecycle:lifecycle-livedata-core:2.0.0-rc01 |
| android.arch.lifecycle:reactivestreams | androidx.lifecycle:lifecycle-reactivestreams:2.0.0-rc01 |
| android.arch.lifecycle:runtime | androidx.lifecycle:lifecycle-runtime:2.0.0-rc01 |
| android.arch.lifecycle:viewmodel | androidx.lifecycle:lifecycle-viewmodel:2.0.0-rc01 |
| android.arch.paging:common | androidx.paging:paging-common:2.0.0-rc01 |
| android.arch.paging:runtime | androidx.paging:paging-runtime:2.0.0-rc01 |
| android.arch.paging:rxjava2 | androidx.paging:paging-rxjava2:2.0.0-rc01 |
| android.arch.persistence.room:common | androidx.room:room-common:2.0.0-rc01 |
| android.arch.persistence.room:compiler | androidx.room:room-compiler:2.0.0-rc01 |
| android.arch.persistence.room:guava | androidx.room:room-guava:2.0.0-rc01 |
| android.arch.persistence.room:migration | androidx.room:room-migration:2.0.0-rc01 |
| android.arch.persistence.room:runtime | androidx.room:room-runtime:2.0.0-rc01 |
| android.arch.persistence.room:rxjava2 | androidx.room:room-rxjava2:2.0.0-rc01 |
| android.arch.persistence.room:testing | androidx.room:room-testing:2.0.0-rc01 |
| android.arch.persistence:db | androidx.sqlite:sqlite:2.0.0-rc01 |
| android.arch.persistence:db-framework | androidx.sqlite:sqlite-framework:2.0.0-rc01 |
| com.android.support.constraint:constraint-layout | androidx.constraintlayout:constraintlayout:1.1.2 |
| com.android.support.constraint:constraint-layout-solver | androidx.constraintlayout:constraintlayout-solver:1.1.2 |
| com.android.support.test.espresso.idling:idling-concurrent | androidx.test.espresso.idling:idling-concurrent:3.1.0 |
| com.android.support.test.espresso.idling:idling-net | androidx.test.espresso.idling:idling-net:3.1.0 |
| com.android.support.test.espresso:espresso-accessibility | androidx.test.espresso:espresso-accessibility:3.1.0 |
| com.android.support.test.espresso:espresso-contrib | androidx.test.espresso:espresso-contrib:3.1.0 |
| com.android.support.test.espresso:espresso-core | androidx.test.espresso:espresso-core:3.1.0 |
| com.android.support.test.espresso:espresso-idling-resource | androidx.test.espresso:espresso-idling-resource:3.1.0 |
| com.android.support.test.espresso:espresso-intents | androidx.test.espresso:espresso-intents:3.1.0 |
| com.android.support.test.espresso:espresso-remote | androidx.test.espresso:espresso-remote:3.1.0 |
| com.android.support.test.espresso:espresso-web | androidx.test.espresso:espresso-web:3.1.0 |
| com.android.support.test.janktesthelper:janktesthelper | androidx.test.jank:janktesthelper:1.0.1 |
| com.android.support.test.services:test-services | androidx.test:test-services:1.1.0 |
| com.android.support.test.uiautomator:uiautomator | androidx.test.uiautomator:uiautomator:2.2.0 |
| com.android.support.test:monitor | androidx.test:monitor:1.1.0 |
| com.android.support.test:orchestrator | androidx.test:orchestrator:1.1.0 |
| com.android.support.test:rules | androidx.test:rules:1.1.0 |
| com.android.support.test:runner | androidx.test: runner :1.1.0 |
| com.android.support:animated-vector-drawable | androidx.vectordrawable:vectordrawable-animated:1.0.0 |
| com.android.support:appcompat-v7 | androidx.appcompat:appcompat:1.0.0 |
| com.android.support:asynclayoutinflater | androidx.asynclayoutinflater:asynclayoutinflater:1.0.0 |
| com.android.support: car | androidx.car: car:1.0.0-alpha5 |
| com.android.support:cardview-v7 | androidx.cardview:cardview:1.0.0 |
| com.android.support:collections | androidx.collection:collection:1.0.0 |
| com.android.support:coordinatorlayout | androidx.coordinatorlayout:coordinatorlayout:1.0.0 |
| com.android.support:cursoradapter | androidx.cursoradapter:cursoradapter:1.0.0 |
| com.android.support:customtabs | androidx.browser:browser:1.0.0 |
| com.android.support:customview | androidx.customview:customview:1.0.0 |
| com.android.support:design | com.google.android.material:material:1.0.0-rc01 |
| com.android.support:documentfile | androidx.documentfile:documentfile:1.0.0 |
| com.android.support:drawerlayout | androidx.drawerlayout:drawerlayout:1.0.0 |
| com.android.support:exifinterface | androidx.exifinterface:exifinterface:1.0.0 |
| com.android.support:gridlayout-v7 | androidx.gridlayout:gridlayout:1.0.0 |
| com.android.support:heifwriter | androidx.heifwriter:heifwriter:1.0.0 |
| com.android.support:interpolator | androidx.interpolator:interpolator:1.0.0 |
| com.android.support:leanback-v17 | androidx.leanback:leanback:1.0.0 |
| com.android.support:loader | androidx.loader:loader:1.0.0 |
| com.android.support:localbroadcastmanager | androidx.localbroadcastmanager:localbroadcastmanager:1.0.0 |
| com.android.support:media2 | androidx.media2:media2:1.0.0-alpha03 |
| com.android.support:media2-exoplayer | androidx.media2:media2-exoplayer:1.0.0-alpha01 |
| com.android.support:mediarouter-v7 | androidx.mediarouter:mediarouter:1.0.0 |
| com.android.support:multidex | androidx.multidex:multidex:2.0.0 |
| com.android.support:multidex-instrumentation | androidx.multidex:multidex-instrumentation:2.0.0 |
| com.android.support:palette-v7 | androidx.palette:palette:1.0.0 |
| com.android.support:percent | androidx.percentlayout:percentlayout:1.0.0 |
| com.android.support:preference-leanback-v17 | androidx.leanback:leanback-preference:1.0.0 |
| com.android.support:preference-v14 | androidx.legacy:legacy-preference-v14:1.0.0 |
| com.android.support:preference-v7 | androidx.preference:preference:1.0.0 |
| com.android.support:print | androidx.print:print:1.0.0 |
| com.android.support:recommendation | androidx.recommendation:recommendation:1.0.0 |
| com.android.support:recyclerview-selection | androidx.recyclerview:recyclerview-selection:1.0.0 |
| com.android.support:recyclerview-v7 | androidx.recyclerview:recyclerview:1.0.0 |
| com.android.support:slices-builders | androidx.slice:slice-builders:1.0.0 |
| com.android.support:slices-core | androidx.slice:slice-core:1.0.0 |
| com.android.support:slices-view | androidx.slice:slice-view:1.0.0 |
| com.android.support:slidingpanelayout | androidx.slidingpanelayout:slidingpanelayout:1.0.0 |
| com.android.support:support-annotations | androidx.annotation:annotation:1.0.0 |
| com.android.support:support-compat | androidx.core:core:1.0.0 |
| com.android.support:support-content | androidx.contentpager:contentpager:1.0.0 |
| com.android.support:support-core-ui | androidx.legacy:legacy-support-core-ui:1.0.0 |
| com.android.support:support-core-utils | androidx.legacy:legacy-support-core-utils:1.0.0 |
| com.android.support:support-dynamic-animation | androidx.dynamicanimation:dynamicanimation:1.0.0 |
| com.android.support:support-emoji | androidx.emoji:emoji:1.0.0 |
| com.android.support:support-emoji-appcompat | androidx.emoji:emoji-appcompat:1.0.0 |
| com.android.support:support-emoji-bundled | androidx.emoji:emoji-bundled:1.0.0 |
| com.android.support:support-fragment | androidx.fragment:fragment:1.0.0 |
| com.android.support:support-media-compat | androidx.media:media:1.0.0 |
| com.android.support:support-tv-provider | androidx.tvprovider:tvprovider:1.0.0 |
| com.android.support:support-v13 | androidx.legacy:legacy-support-v13:1.0.0 |
| com.android.support:support-v4 | androidx.legacy:legacy-support-v4:1.0.0 |
| com.android.support:support-vector-drawable | androidx.vectordrawable:vectordrawable:1.0.0 |
| com.android.support:swiperefreshlayout | androidx.swiperefreshlayout:swiperefreshlayout:1.0.0 |
| com.android.support:textclassifier | androidx.textclassifier:textclassifier:1.0.0 |
| com.android.support:transition | androidx.transition:transition:1.0.0 |
| com.android.support:versionedparcelable | androidx.versionedparcelable:versionedparcelable:1.0.0 |
| com.android.support:viewpager | androidx.viewpager:viewpager:1.0.0 |
| com.android.support:wear | androidx.wear:wear:1.0.0 |
| com.android.support:webkit | androidx.webkit:webkit:1.0.0 |
3、调整class。
替换后，会有非常多的错误出现，那是因为涉及到的class也需要更换成androidx对应包下的class。
如，把
android.arch.core.executor.ArchTaskExecutor 换为androidx.arch.core.executor.ArchTaskExecutor
OK，整理完毕。
