Easiest way to detect Enter key being pressed is:
mPasswordField.setOnEditorActionListener(new TextView.OnEditorActionListener() {
@Override
public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
if (event!= null) { // KeyEvent: If triggered by an enter key, this is the event; otherwise, this is null.
signIn(mEmailField.getText().toString(), mPasswordField.getText().toString());
return true;
} else {
return false;
}
}
});