Android SDK 28 - versionCode in PackageInfo has been deprecated

My recommended solution:

Include this in your main build.gradle :

implementation 'androidx.appcompat:appcompat:1.0.2'

then just use this code:

PackageInfo pInfo = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
long longVersionCode= PackageInfoCompat.getLongVersionCode(pInfo);
int versionCode = (int) longVersionCode; // avoid huge version numbers and you will be ok

In case you have problems adding appcompat library then just use this alternative solution:

final PackageInfo pInfo = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
int versionCode;
if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
    versionCode = (int) pInfo.getLongVersionCode(); // avoid huge version numbers and you will be ok
} else {
    //noinspection deprecation
    versionCode = pInfo.versionCode;
}

Just for others using Xamarin, my answer was:

public long GetBuild()
{
    var context = global::Android.App.Application.Context;
    PackageManager manager = context.PackageManager;
    PackageInfo info = manager.GetPackageInfo(context.PackageName, 0);

    return info.LongVersionCode;
}

It says what to do on the Java doc (I recommend not using the Kotlin documentation for much; it's not really maintained well):

versionCode

This field was deprecated in API level 28. Use getLongVersionCode() instead, which includes both this and the additional versionCodeMajor attribute. The version number of this package, as specified by the tag's versionCode attribute.

This is an API 28 method, though, so consider using PackageInfoCompat. It has one static method:

getLongVersionCode(PackageInfo info)