1. 添加绑定设置

如上一篇文章（Android - DataBinding）一样，在 build.gradle 中添加

buildFeatures{
    dataBinding true
}

2. 添加ViewModel类

MyViewModel.java：

public class MyViewModel extends ViewModel {
    private MutableLiveData<Integer> mATeamScore;	// Team A 的分数
    private MutableLiveData<Integer> mBTeamScore;	// Team B 的分数

    private int mATeamLastScore;
    private int mBTeamLastScore;

    public MutableLiveData<Integer> getATeamScore() {
        if (mATeamScore == null) {
            mATeamScore = new MutableLiveData<>();
            mATeamScore.setValue(0);
        }
        return mATeamScore;
    }

    public MutableLiveData<Integer> getBTeamScore() {
        if (mBTeamScore == null) {
            mBTeamScore = new MutableLiveData<>();
            mBTeamScore.setValue(0);
        }
        return mBTeamScore;
    }

    public void addScoreToA(int i) {
        saveLastScore();
        mATeamScore.setValue(mATeamScore.getValue() + i);
    }

    public void addScoreToB(int i) {
        saveLastScore();
        mBTeamScore.setValue(mBTeamScore.getValue() + i);
    }

    public void resetScore() {
        mATeamScore.setValue(0);
        mBTeamScore.setValue(0);
    }

    public void undoScore() {
        mATeamScore.setValue(mATeamLastScore);
        mBTeamScore.setValue(mBTeamLastScore);
    }

    private void saveLastScore() {
        mATeamLastScore = mATeamScore.getValue();
        mBTeamLastScore = mBTeamScore.getValue();
    }
}

3. activity_main.xml添加绑定

<?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="myViewModel"
            type="com.example.databindingviewmodellivedata.MyViewModel"/>
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal"
        tools:context=".MainActivity">

        <LinearLayout
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginTop="20dp"
            android:orientation="vertical">

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                android:text="Team A"
                android:textSize="20sp" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                android:layout_marginTop="10dp"
                android:text="@{String.valueOf(myViewModel.getATeamScore())}"
                android:textSize="50sp"
                android:textColor="#2196F3" />

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:layout_gravity="center"
                android:text="+1"
                android:onClick="@{()->myViewModel.addScoreToA(1)}"/>

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:layout_gravity="center"
                android:text="+2"
                android:onClick="@{()->myViewModel.addScoreToA(2)}"/>

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:layout_gravity="center"
                android:text="+3"
                android:onClick="@{()->myViewModel.addScoreToA(3)}"/>

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="30dp"
                android:layout_gravity="center"
                android:text="退一步"
                android:onClick="@{()->myViewModel.undoScore()}"/>

        </LinearLayout>

        <LinearLayout
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:layout_marginTop="20dp"
            android:orientation="vertical">

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                android:text="Team B"
                android:textSize="20sp" />

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                android:layout_marginTop="10dp"
                android:text="@{String.valueOf(myViewModel.getBTeamScore())}"
                android:textSize="50sp"
                android:textColor="#E91E63" />

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:layout_gravity="center"
                android:text="+1"
                android:onClick="@{()->myViewModel.addScoreToB(1)}"/>

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:layout_gravity="center"
                android:text="+2"
                android:onClick="@{()->myViewModel.addScoreToB(2)}"/>

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="20dp"
                android:layout_gravity="center"
                android:text="+3"
                android:onClick="@{()->myViewModel.addScoreToB(3)}"/>

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="30dp"
                android:layout_gravity="center"
                android:text="重置"
                android:onClick="@{()->myViewModel.resetScore()}"/>

        </LinearLayout>

    </LinearLayout>
</layout>

4. MainActivity.java添加绑定

public class MainActivity extends AppCompatActivity {

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

        ActivityMainBinding activityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main);

        MyViewModel myViewModel = new ViewModelProvider(this, new ViewModelProvider.AndroidViewModelFactory(getApplication())).get(MyViewModel.class);
        activityMainBinding.setMyViewModel(myViewModel);
        activityMainBinding.setLifecycleOwner(this);
    }
}