activity_register.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools">
    <data>
        <variable
            name="form"
            type="pl.brightinventions.databinding.RegisterForm"/>
    </data>

    <RelativeLayout android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    style="@style/Container.Padded"
                    tools:context=".EditorActivity"
                    android:animateLayoutChanges="true">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/first_name_hint"
            android:visibility="@{form.firstNameLabelVisibility}"
            android:theme="@style/Label.Small"/>

        <EditText
            android:id="@+id/first_name"
            android:text="@{form.firstName}"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="20dp"
            android:hint="@string/first_name_hint"
            android:inputType="textPersonName"/>

        <TextView
            android:id="@+id/error"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_above="@+id/register"
            android:text="@{form.error}"/>

        <Button
            android:id="@+id/register"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/register"
            android:layout_alignParentBottom="true"/>

    </RelativeLayout>
</layout>

RegisterActivity.java

import pl.brightinventions.databinding.databinding.ActivityRegisterBinding;

public class RegisterActivity extends Activity {
    RegisterApi registerApi; // inject or create remote api
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ActivityRegisterBinding viewDataBinding = DataBindingUtil.setContentView(this, R.layout.activity_register);

        final RegisterForm form = new RegisterForm();

        View root = viewDataBinding.getRoot();

        EditText firstName = (EditText) root.findViewById(R.id.first_name);
        firstName.addTextChangedListener(new TextWatcherBase() {
            @Override
            public void afterTextChanged(Editable s) {
                form.setFirstNameFromView(s.toString());
            }
        });

        viewDataBinding.setForm(form);

        findViewById(R.id.register).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                registerApi.register(form.newRegisterData(), new OnRegistrationCompleted(form));
            }
        });
    }

    private static final class OnRegistrationCompleted
            implements Action2<RegisterApi.RegistrationDto,Throwable> {
        private final RegisterForm form;

        public OnRegistrationCompleted(RegisterForm form) {
            this.form = form;
        }
        
        @Override
        public void call(RegisterApi.RegistrationDto registrationDto, Throwable error) {
            this.form.setError(error);
        }
    }
}

RegisterForm.java

public class RegisterForm extends BaseObservable {
    @Bindable
    public String firstName;

    @Bindable
    public int getFirstNameLabelVisibility(){
        return TextUtils.isEmpty(firstName) ? View.INVISIBLE : View.VISIBLE;
    }

    public void setFirstNameFromView(String firstNameFromView) {
        firstName = firstNameFromView;
        notifyPropertyChanged(pl.brightinventions.databinding.BR.firstNameLabelVisibility);
    }

    @Bindable
    public String error;

    public void setError(Throwable error) {
        this.error = error.getLocalizedMessage();
        notifyPropertyChanged(pl.brightinventions.databinding.BR.error);
    }

    public RegisterApi.RegistrationDto newRegisterData() {
        RegisterApi.RegistrationDto dto = new RegisterApi.RegistrationDto();
        dto.firstName = firstName;
        return dto;
    }
}