gistfile1.txt

/*
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <EditText
        android:id="@+id/edit_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/text_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>
*/
package com.xxx.home;

import android.arch.core.util.Function;
import android.arch.lifecycle.LiveData;
import android.arch.lifecycle.MutableLiveData;
import android.arch.lifecycle.Observer;
import android.arch.lifecycle.Transformations;
import android.arch.lifecycle.ViewModel;
import android.arch.lifecycle.ViewModelProvider;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private String string;

    @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {
        super.onSaveInstanceState(savedInstanceState);
        savedInstanceState.putString("STRING", string);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (savedInstanceState != null) {
            this.string = savedInstanceState.getString("STRING");
        }

        final TextView textView = this.findViewById(R.id.text_view);

        ViewModelFactory factory = new ViewModelFactory(this.string);
        final MyViewModel myViewModel = android.arch.lifecycle.ViewModelProviders.of(this, factory).get(MyViewModel.class);
        myViewModel.getCode().observe(this, new Observer<Integer>() {
            @Override
            public void onChanged(@Nullable Integer integer) {
                textView.setText("" + integer);
                android.util.Log.i("CHEOK", "UI -> " + integer);
            }
        });

        EditText editText = this.findViewById(R.id.edit_text);
        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) {
                string = editable.toString();
                myViewModel.search(string);
            }
        });
    }

    class MyViewModel extends ViewModel {
        final MutableLiveData<String> mString = new MutableLiveData<>();
        final LiveData<Integer> mCode;


        public MyViewModel(String string) {

            mCode = Transformations.switchMap(mString, new Function<String, LiveData<Integer>>() {
                @Override
                public LiveData<Integer> apply(final String input) {
                    final MutableLiveData<Integer> result = new MutableLiveData<>();

                    new Thread(new Runnable() {
                        @Override
                        public void run() {
                            // Pretend we are busy
                            try {
                                Thread.sleep(5000);
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }

                            int code = 0;
                            for (int i=0; i<input.length(); i++) {
                                code = code + (int)input.charAt(i);
                            }

                            android.util.Log.i("CHEOK", "Processing : " + input + " -> " + code);

                            result.postValue(code);
                        }
                    }).start();

                    return result;
                }
            });

            if (string != null) {
                mString.setValue(string);
            }
        }

        public LiveData<Integer> getCode() {
            return mCode;
        }

        public void search(String string) {
            mString.setValue(string);
        }
    }

    class ViewModelFactory implements ViewModelProvider.Factory {
        private final String string;

        public ViewModelFactory(String string) {
            this.string = string;
        }

        @Override
        public MyViewModel create(Class modelClass) {
            return new MyViewModel(string);
        }
    }
}