+ void validateAmount() {
+ amountValid.setValue(true);
+ }
+ void invalidateAmount() {
+ amountValid.setValue(false);
+ }
+ void observeAmountValidity(NewTransactionActivity activity, Observer<Boolean> observer) {
+ amountValid.observe(activity, observer);
+ }
+ void stopObservingAmountValidity(Observer<Boolean> observer) {
+ amountValid.removeObserver(observer);
+ }