转载‘’
https://blog.csdn.net/guolin_blog/article/details/97142065
一句话总结：
1： AndroidX 是针对 Android Support Library进行的一次升级，升级内容主要在以下几个方面
第一，包名。之前Android Support Library中的API，它们的包名都是在android.support.*下面的，而AndroidX库中所有API的包名都变成了在androidx.*下面。这是一个很大的变化，意味着以后凡是android.*包下面的API都是随着Android操作系统发布的，而androidx.*包下面的API都是随着扩展库发布的，这些API基本不会依赖于操作系统的具体版本。
第二，命名规则。吸取了之前命名规则的弊端，AndroidX所有库的命名规则里都不会再包含具体操作系统API的版本号了。比如，像appcompat-v7库，在AndroidX中就变成了appcompat库。
2：格式：implementation 'androidx.appcompat:appcompat:1.1.0'
3：使用：比如之前你经常使用的RecyclerView、ViewPager等等库，在AndroidX中都会有一个对应的版本，只要改一下包名就可以完全无缝使用，用法方面基本上都没有任何的变化
watch : AndroidX和Android Support Library中的库是非常不建议混合在一起使用的，因为它们可能会产生很多不兼容的问题。最好的做法是，要么全部使用AndroidX中的库，要么全部使用Android Support Library中的库
4: 老项目迁移到 AndroidX
as 有一键迁移功能 ：为此，Android Studio提供了一个一键迁移的功能，只需要对着你的项目名右击 → Refactor → Migrate to AndroidX，就会弹出如下图所示的窗口。
5： support 包和 AndroidX 版本对照
| 旧包 | AndroidX |
|---|---|
| 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 |
6： 有以下几种情况不要入坑
6.1 对于引入了 三方的东西.androidx 迁移还是很麻烦
6.2 新项目中用的androidx,和原来的support v7不兼容出错
7： support包
背景： 举个例子，当Android系统发布到3.0版本的时候，突然意识到了平板电脑的重要性，因此为了让Android可以更好地兼容平板，Android团队在3.0系统（API 11）中加入了Fragment功能。但是Fragment的作用并不只局限于平板，以前的老系统中也想使用这个功能该怎么办？于是Android团队推出了一个鼎鼎大名的Android Support Library，用于提供向下兼容的功能。比如我们每个人都熟知的support-v4库，appcompat-v7库都是属于Android Support Library的，这两个库相信任何做过Android开发的人都使用过。
supportV4
supportV7
但是慢慢随着时间的推移，什么1.6、2.1系统早就已经被淘汰了，现在Android官方支持的最低系统版本已经是4.0.1，对应的API版本号是15。support-v4、appcompat-v7库也不再支持那么久远的系统了，但是它们的名字却一直保留了下来，虽然它们现在的实际作用已经对不上当初命名的原因了。
那么很明显，Android团队也意识到这种命名已经非常不合适了，于是对这些API的架构进行了一次重新的划分，推出了AndroidX。因此，AndroidX本质上其实就是对Android Support Library进行的一次升级，升级内容主要在于以下两个方面。