final onUpgrade = OnUpgrade();
final isNewVersion = await onUpgrade.isNewVersion();
if (isNewVersion.state == UpgradeState.upgrade) {
  myDataMigrationOrNewFeatureDialog(isNewVersion.currentVersion!);
  await onUpgrade.updateLastVersion();
}

void myDataMigrationOrNewFeatureDialog(String version) {
  ...
}

final upgrades = {
  '1.0.0': myDataMigrationOrNewFeatureDialogForVersion1,
  '1.5.0': myDataMigrationOrNewFeatureDialogForVersion15
};

final onMultipleUpgrade = OnUpgrade();
final isNewVersionMultiple = await onMultipleUpgrade.isNewVersion();
if (isNewVersionMultiple.state == UpgradeState.upgrade) {
  await isNewVersionMultiple.executeUpgrades(upgrades);
  await onMultipleUpgrade.updateLastVersion();
}

Future<void> myDataMigrationOrNewFeatureDialogForVersion1() async {
  // Upgrade method can be async
}

void myDataMigrationOrNewFeatureDialogForVersion15() {
  // Upgrade method can be sync
}

Future<String> customVersionGetter() async {
    // Your implementation. Load the last known version.
    // Must return an empty string if no initial version is known (on the first app start, before updateLastVersion() was called the first time).
}

Future<bool> customVersionSetter([String? version]) async {
    // Your implementation. Update the last known version.
    // Perform the upgrade check before calling this function.
}

final onUpgradeCustom = OnUpgrade(customVersionUpdate: customVersionSetter, customVersionLookup: customVersionGetter);
final isCustomNewVersion = await onUpgradeCustom.isNewVersion();
if (isCustomNewVersion.state == UpgradeState.upgrade) {
  myDataMigrationOrNewFeatureDialog(isCustomNewVersion.currentVersion!);
  await onUpgrade.updateLastVersion();
}

void myDataMigrationOrNewFeatureDialog(String version) {
  ...
}