EditText validation in MVVM

activity_second.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools">

  <data>

    <variable
      name="model"
      type="kr.changhoonjin.testmvp.view_models.Second"/>
  </data>

  <android.support.constraint.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="kr.changhoonjin.testmvp.views.SecondActivity">

    <EditText
      android:id="@+id/edit_name"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:hint="Name"
      android:inputType="textPersonName"
      android:text="@{model.name}"
      app:addTextChangedListener="@{model.nameWatcher}"
      app:layout_constraintLeft_toLeftOf="parent"
      app:layout_constraintRight_toRightOf="parent"/>

    <EditText
      android:id="@+id/edit_email"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:hint="Email"
      android:inputType="textEmailAddress"
      android:text="@{model.email}"
      app:addTextChangedListener="@{model.emailWatcher}"
      app:layout_constraintLeft_toLeftOf="parent"
      app:layout_constraintRight_toRightOf="parent"
      app:layout_constraintTop_toBottomOf="@+id/edit_name"/>

    <RatingBar
      android:id="@+id/rating"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:rating="@{model.score}"
      android:stepSize="1"
      app:OnRatingBarChangeListener="@{model.ratingBarChangeListener}"
      app:layout_constraintLeft_toLeftOf="parent"
      app:layout_constraintRight_toRightOf="parent"
      app:layout_constraintTop_toBottomOf="@+id/edit_email"/>

    <Button
      android:id="@+id/btn1"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:enabled="@{model.isValid}"
      android:onClick="@{()->model.publish()}"
      android:text="게시"
      app:layout_constraintLeft_toLeftOf="parent"
      app:layout_constraintRight_toRightOf="parent"
      app:layout_constraintTop_toBottomOf="@+id/rating"/>
  </android.support.constraint.ConstraintLayout>
</layout>

Second.java

package kr.changhoonjin.testmvp.view_models;

import android.databinding.ObservableBoolean;
import android.databinding.ObservableField;
import android.databinding.ObservableInt;
import android.text.Editable;
import android.text.TextUtils;
import android.text.TextWatcher;
import android.util.Log;
import android.util.Patterns;
import android.widget.RatingBar;

public class Second implements ViewModel {
  public final ObservableField<String> name = new ObservableField<>();
  public final ObservableField<String> email = new ObservableField<>();
  public final ObservableInt score = new ObservableInt();
  public final ObservableBoolean isValid = new ObservableBoolean();

  @Override public void onCreate() {
    score.set(0);
    isValid.set(false);
  }

  @Override public void onResume() {}

  @Override public void onPause() {}

  @Override public void onDestroy() {}

  private void validation() {
    boolean isValidName = !TextUtils.isEmpty(name.get());
    boolean isValidEmail = !TextUtils.isEmpty(email.get()) && Patterns.EMAIL_ADDRESS.matcher(email.get()).matches();
    boolean isValidScore = score.get() > 0;
    isValid.set(isValidName && isValidEmail && isValidScore);
  }

  public void publish() {
    Log.w("==== [App] === Second | publish", "|" + "publish");
  }

  /***************************
   * listener
   ***************************/
  public TextWatcher nameWatcher() {
    return 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) {
        name.set(charSequence.toString());
      }

      @Override public void afterTextChanged(Editable editable) {
        validation();
      }
    };
  }

  public TextWatcher emailWatcher() {
    return 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) {
        email.set(charSequence.toString());
      }

      @Override public void afterTextChanged(Editable editable) {
        validation();
      }
    };
  }

  public RatingBar.OnRatingBarChangeListener ratingBarChangeListener = (ratingBar, rating, fromUser) -> {
    score.set((int) rating);
    validation();
  };
}

how can i call set error?

Bad code

Your ViewModel contains Android packages. TextWatchers code! What's the point of MVVM ?

@anupamchugh I've seen people doing the same stuff for focus change listener too. What's your way of doing this? Please share your ideas on how to maintain MVVM pattern & share your sample code too