How to set error on EditText using DataBinding Framework MVVM

Question

I am using Android Data Binding framework I have suppose an EditText for login form with username as below

Answer 1

I just want to share my modification of the answer of Long Ranger for android arch viewModel:

    public class StringValidationRules {

    public static StringRule NOT_EMPTY = new StringRule() {
        @Override
        public boolean validate(Editable s) {
            return TextUtils.isEmpty(s.toString());
        }
    };

    public static StringRule EMAIL = new StringRule() {
        @Override
        public boolean validate(Editable s) {
            return !android.util.Patterns.EMAIL_ADDRESS.matcher(s).matches();

        }
    };

    public static StringRule PASSWORD = new StringRule() {
        @Override
        public boolean validate(Editable s) {
            return s.length() < 8;
        }
    };

    public interface StringRule {
        boolean validate(Editable s);
    }
}

the viewModel...

    public class LoginViewModel extends ViewModel {
...
@BindingAdapter({"app:validation", "app:errorMsg"})
    public static void setErrorEnable(EditText editText, StringValidationRules.StringRule stringRule, final String errorMsg) {
        editText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {

            }

            @Override
            public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {

            }

            @Override
            public void afterTextChanged(Editable editable) {
                if (stringRule.validate(editText.getText())) {
                    editText.setError(errorMsg);
                } else {
                    editText.setError(null);
                }
            }
        });
    }

...

and the XML:

    
        
        
    

...