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

Manually adding android.useAndroidX=true and android.enableJetifier=true giving me hard time. Because it's throw some error or Suggestion: add 'tools:replace="android:appComponentFactory"' to <application>

To Enable Jet-fire in project there is option in android Studio

Select Your Project ---> Right Click

app----> Refactor ----> Migrate to AndroidX

Shown in below image:-

After click on Migrate to AndroidX.

It will ask for confirmation and back up for your project.

And last step it will ask you for to do refactor.

After doing Refactor check your gradle.properties have android.useAndroidX=true and android.enableJetifier=true. If they are not then add these two lines to your gradle.properties file:

android.useAndroidX=true
android.enableJetifier=true

Note:- Upgrading using Android Studio, this option works if you have android studio 3.2 and onward. Check this

You need not to worry

Just enable Jetifier in your projet.

• Update Android Studio to 3.2.0 or newer.

• Open gradle.properties and add below two lines.

  android.enableJetifier=true
  android.useAndroidX=true
  

It will convert all support libraries of your dependency to AndroidX at run time (you may have compile time errors, but app will run).

Add the lines in the gradle.properties file

android.useAndroidX=true
android.enableJetifier=true

Refer also https://developer.android.com/jetpack/androidx

I added below two lines in gradle.properties file

android.useAndroidX=true
android.enableJetifier=true

then I got the following error

error: package android.support.v7.app does not exist
import android.support.v7.app.AlertDialog;
                         ^
                         

I have removed the imports and added below line

import static android.app.AlertDialog.*;

And the classes which are extended from AppCompactActivity, added the below line. (For these errors you just need to press alt+enter in android studio which will import the correct library for you. Like this you can resolve all the errors)

import androidx.appcompat.app.AppCompatActivity;

In your xml file if you have used any

<android.support.v7.widget.Toolbar 

replace it with androidx.appcompat.widget.Toolbar

then in your java code

import androidx.appcompat.widget.Toolbar;