There's this sample repository, which showcases different Android testing practices. One of the apps is android-testing/unit/BasicSample, which is very simple and, among other things, checks the email field and for that purpose adds a listener like this:
mEmailText.addTextChangedListener(mEmailValidator);
And then on save it checks
if (!mEmailValidator.isValid()) {
mEmailText.setError("Invalid email");
}
Why not just have a simple utility class which will perform this check only when the Save button is pressed and not on each character change?