How to Use Library That Used Android Support with Androidx Projects

Can I use library that used android support with Androidx projects.

You can enable Jetifier on your project, which will basically exchange the Android Support Library dependencies in your project dependencies with AndroidX-ones. (e.g. Your Lottie dependencies will be changed from Support to AnroidX)

From the Android Studio Documentation (https://developer.android.com/studio/preview/features/):

The Android Gradle plugin provides the following global flags that you
can set in your gradle.properties file:

android.useAndroidX: When set to true, this flag indicates that you want to start using AndroidX from now on. If the flag is absent,
Android Studio behaves as if the flag were set to false.

android.enableJetifier: When set to true, this flag indicates that you want to have tool support (from the Android Gradle plugin) to
automatically convert existing third-party libraries as if they were
written for AndroidX. If the flag is absent, Android Studio behaves as
if the flag were set to false.

Precondition for Jetifier:

you have to use at least Android Studio 3.2

To enable jetifier, add those two lines to your gradle.properties file:

android.useAndroidX=true
android.enableJetifier=true

Finally, please check the release notes of AndroidX, because jetifier has still some problems with some libraries (e.g. Dagger Android): https://developer.android.com/topic/libraries/support-library/androidx-rn

Can I use library that uses Androidx with support library project?

Using support libraries is not a recommended practice anymore, and you should migrate to androidx as soon as possible. Migration is easy, and Android Studio takes care of the heavy lifting for you.

Can I use a Library that used AndroidX with an android support project?

No, I don't think you can.

But you can the other way! So there should be no reason not to migrate your own project to AndroidX.

Android Studio 3.6.1 | Error: This project uses AndroidX dependencies

The Android Gradle plugin provides the following global flags that you
can set in your gradle.properties file:
android.useAndroidX: When set to true, this flag indicates that you
want to start using AndroidX from now on. If the flag is absent,
Android Studio behaves as if the flag were set to false.
android.enableJetifier: When set to true, this flag indicates that you
want to have tool support (from the Android Gradle plugin) to
automatically convert existing third-party libraries as if they were
written for AndroidX. If the flag is absent, Android Studio behaves as
if the flag were set to false.

To enable jetifier, add those two lines to your gradle.properties file:

android.useAndroidX=true
android.enableJetifier=true

Is there a way to mix AndroidX and a subproject that uses the support library?

All modules used in your app need to move to AndroidX together. You'd need to move your module you want to keep on Support Library into a new project and only use it as a maven dependency or AAR in your AndroidX project.