Unable to migrate Flutter project to AndroidX

I was able to resolve my issue:

1. Open the Flutter project into Android Studio
2. Right click on the android directory, click on Flutter -> Open Android module in Android Studio. It asked me to upgrade my gradle plugin.
3. Then I installed Google Play Services. Tools -> SDK Manager -> SDK Tools and check the Google Play Services.

After the Google Play Services Installed, I did Refactor -> Migrate to AndroidX. It started working.

Note: Do the refactor from the project window you opened in the step 2.

Here is how I got rid of "compileSdkVersion 28" error. But before I solved it this way, I upgraded Android Studio IDE from 3.4.1 -> 3.5.1. I am not sure if this was really needed. So whatever version of IDE you have, see if you can use following steps to solve it.

1. Go to "Project Structure" - (2nd icon on left of AVD Manager icon on top right corner of IDE)

2. On "Project Structure" dialog under left navigation click on Project Settings->Modules

3. After selecting Modules, on the right pane you should see 3 tabs Sources, Paths, Dependencies

4. Click on Dependencies, if you are getting compileSdkVersion 28 error the SDK version under Dependencies is pointing to version lower than 28 -> Select 28 or higher

5. Click OK

6. Now Refactor->Migrate to AndroidX worked for me

In gradle.build (app) add this

 compileSdkVersion 28
    defaultConfig {
        ......
        minSdkVersion 21
        targetSdkVersion 28
        ......
    }

And there are some implementations required to use androidx :-

implementation 'androidx.appcompat:appcompat:1.1.0-alpha01'
implementation 'androidx.legacy:legacy-support-v4:1.0.0'

And add these given two lines(below) to gradle.properties:-

android.useAndroidX=true
android.enableJetifier=true