Android : 篮球记分器app

示例图：

1.导包在build.gradle 中加入

    // 使用androidx版本库
    implementation 'androidx.lifecycle:lifecycle-extensions:2.1.0-alpha03'

2. 开启dataBinding

android{
    ...

     // 步骤1.开启data binding
    dataBinding {
        enabled = true
    }
    
    ...

}

3.写个类继承 ViewModel

package com.example.mydatabindingtest;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class MyViewModel extends ViewModel {
    private MutableLiveData<Integer> redNumb;
    private MutableLiveData<Integer> greenNumb;

    //回滚 用于记录前面一次的值
    private int redBack,greenBack;
    public MutableLiveData<Integer> getRedNumb() {
        if (redNumb == null) {
            redNumb = new MutableLiveData<>();
            redNumb.setValue(0);
        }
        return redNumb;
    }

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

    public void redAdd(int num) {
        //添加之前保留之前的值 都记录下
        redBack = redNumb.getValue();
        greenBack = greenNumb.getValue();

        redNumb.setValue(getRedNumb().getValue() + num);
    }


    public void greenAdd(int num) {
        //添加之前保留之前的值 都记录下
        redBack = redNumb.getValue();
        greenBack = greenNumb.getValue();

        greenNumb.setValue(getGreenNumb().getValue() + num);
    }

    //重置
    public void reset(){
        //添加之前保留之前的值
        greenBack = greenNumb.getValue();
        redBack = redNumb.getValue();

        redNumb.setValue(0);
        greenNumb.setValue(0);
    }


    //撤销一次
    public void rollBack(){
        //把记录的值设置到变量中
        redNumb.setValue(redBack);
        greenNumb.setValue(greenBack);
    }
}

4.更改布局 activity_main.xml

<?xml version="1.0" encoding="utf-8"?>

<!-- 步骤2. 点击小灯泡生成新的xml 或者自己更改 -->
<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="data"
            type="com.example.mydatabindingtest.MyViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/btn_add1"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline22"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.45" />

        <Button
            android:id="@+id/btn_green_add3"
            style="@style/Widget.AppCompat.Button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:background="#00FFE7"
            android:onClick="@{() -> data.greenAdd(3)}"
            android:scrollbarThumbHorizontal="@null"
            android:scrollbarThumbVertical="@null"
            android:text="@string/text_add3"
            android:textColor="#0288D1"
            android:textColorHighlight="@null"
            android:textColorHint="@null"
            android:textColorLink="@null"
            android:textSize="30sp"
            android:textStyle="bold"
            app:layout_constraintBottom_toTopOf="@+id/guideline16"
            app:layout_constraintEnd_toStartOf="@+id/guideline19"
            app:layout_constraintStart_toStartOf="@+id/guideline9"
            app:layout_constraintTop_toTopOf="@+id/guideline15"
            tools:ignore="DuplicateSpeakableTextCheck,VisualLintButtonSize" />

        <Button
            android:id="@+id/btn_red_add1"
            style="@style/Widget.AppCompat.Button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:background="#FFff0000"
            android:onClick="@{() -> data.redAdd(1)}"
            android:scrollbarThumbHorizontal="@null"
            android:scrollbarThumbVertical="@null"
            android:text="@string/text_add1"
            android:textColor="@color/white"
            android:textColorHighlight="@null"
            android:textColorHint="@null"
            android:textColorLink="@null"
            android:textSize="30sp"
            android:textStyle="bold"
            app:layout_constraintBottom_toTopOf="@+id/guideline14"
            app:layout_constraintEnd_toStartOf="@+id/guideline22"
            app:layout_constraintStart_toStartOf="@+id/guideline18"
            app:layout_constraintTop_toTopOf="@+id/guideline13"
            app:layout_constraintVertical_bias="0.52"
            tools:ignore="DuplicateSpeakableTextCheck,VisualLintButtonSize" />

        <Button
            android:id="@+id/btn_green_add1"
            style="@style/Widget.AppCompat.Button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:background="#00FFE7"
            android:onClick="@{() -> data.greenAdd(1)}"
            android:scrollbarThumbHorizontal="@null"
            android:scrollbarThumbVertical="@null"
            android:text="@string/text_add1"
            android:textColor="#0288D1"
            android:textColorHighlight="@null"
            android:textColorHint="@null"
            android:textColorLink="@null"
            android:textSize="30sp"
            android:textStyle="bold"
            app:layout_constraintBottom_toTopOf="@+id/guideline14"
            app:layout_constraintEnd_toStartOf="@+id/guideline19"
            app:layout_constraintStart_toStartOf="@+id/guideline9"
            app:layout_constraintTop_toTopOf="@+id/guideline13"
            tools:ignore="VisualLintButtonSize" />

        <Button
            android:id="@+id/btn_green_add2"
            style="@style/Widget.AppCompat.Button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:background="#00FFE7"
            android:onClick="@{() -> data.greenAdd(2)}"
            android:scrollbarThumbHorizontal="@null"
            android:scrollbarThumbVertical="@null"
            android:text="@string/text_add2"
            android:textColor="#0288D1"
            android:textColorHighlight="@null"
            android:textColorHint="@null"
            android:textColorLink="@null"
            android:textSize="30sp"
            android:textStyle="bold"
            app:layout_constraintBottom_toTopOf="@+id/guideline15"
            app:layout_constraintEnd_toStartOf="@+id/guideline19"
            app:layout_constraintStart_toStartOf="@+id/guideline9"
            app:layout_constraintTop_toTopOf="@+id/guideline14"
            tools:ignore="DuplicateSpeakableTextCheck,VisualLintButtonSize" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline9"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.55" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline10"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.05" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline11"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.1504788" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline13"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.35" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline14"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.45" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline15"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.55" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline16"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.65" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline17"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.75" />

        <TextView
            android:textColor="@color/white"
            android:gravity="center"
            android:id="@+id/textView"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:background="#FFff0000"
            android:text="@string/text_A"
            android:textSize="20sp"
            app:layout_constraintBottom_toTopOf="@+id/guideline11"
            app:layout_constraintEnd_toStartOf="@+id/guideline22"
            app:layout_constraintStart_toStartOf="@+id/guideline18"
            app:layout_constraintTop_toTopOf="@+id/guideline10" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:background="#00FFE7"
            android:gravity="center"
            android:text="@string/text_B"
            android:textColor="#0288D1"
            android:textSize="20sp"
            app:layout_constraintBottom_toTopOf="@+id/guideline11"
            app:layout_constraintEnd_toStartOf="@+id/guideline19"
            app:layout_constraintStart_toStartOf="@+id/guideline9"
            app:layout_constraintTop_toTopOf="@+id/guideline10" />

        <TextView
            android:id="@+id/text_red"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="@{String.valueOf(data.redNumb)}"
            android:textColor="@color/btn_bg"
            android:textSize="50sp"
            app:layout_constraintBottom_toTopOf="@+id/guideline13"
            app:layout_constraintEnd_toStartOf="@+id/guideline22"
            app:layout_constraintStart_toStartOf="@+id/guideline18"
            app:layout_constraintTop_toTopOf="@+id/guideline11"
            app:layout_constraintVertical_bias="0.526" />

        <TextView
            android:id="@+id/text_green"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginTop="4dp"
            android:gravity="center"
            android:text="@{String.valueOf(data.greenNumb)}"
            android:textColor="#0288D1"
            android:textColorHighlight="@null"
            android:textColorHint="@null"
            android:textColorLink="@null"
            android:textSize="50sp"
            app:layout_constraintBottom_toTopOf="@+id/guideline13"
            app:layout_constraintEnd_toStartOf="@+id/guideline19"
            app:layout_constraintHorizontal_bias="1.0"
            app:layout_constraintStart_toStartOf="@+id/guideline9"
            app:layout_constraintTop_toTopOf="@+id/guideline11" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline18"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.05" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline19"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.95" />

        <ImageView
            android:id="@+id/img_rollback"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:contentDescription="@string/img_rollback_alt"
            android:onClick="@{() -> data.rollBack()}"
            app:layout_constraintBottom_toTopOf="@+id/guideline17"
            app:layout_constraintEnd_toStartOf="@+id/guideline9"
            app:layout_constraintHorizontal_bias="0.38"
            app:layout_constraintStart_toStartOf="@+id/guideline18"
            app:layout_constraintTop_toTopOf="@+id/guideline16"
            app:layout_constraintVertical_bias="0.166"
            app:srcCompat="@drawable/baseline_reply" />

        <ImageView
            android:id="@+id/img_reset"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:contentDescription="@string/img_reset_alt"
            android:onClick="@{() -> data.reset()}"
            app:layout_constraintBottom_toTopOf="@+id/guideline17"
            app:layout_constraintEnd_toStartOf="@+id/guideline19"
            app:layout_constraintHorizontal_bias="0.521"
            app:layout_constraintStart_toStartOf="@+id/guideline9"
            app:layout_constraintTop_toTopOf="@+id/guideline16"
            app:layout_constraintVertical_bias="0.166"
            app:srcCompat="@drawable/baseline_cached_24" />

        <Button
            android:id="@+id/btn_red_add2"
            style="@style/Widget.AppCompat.Button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:background="#FFff0000"
            android:onClick="@{() -> data.redAdd(2)}"
            android:scrollbarThumbHorizontal="@null"
            android:scrollbarThumbVertical="@null"
            android:text="@string/text_add2"
            android:textColor="@color/white"
            android:textColorHighlight="@null"
            android:textColorHint="@null"
            android:textColorLink="@null"
            android:textSize="30sp"
            android:textStyle="bold"
            app:layout_constraintBottom_toTopOf="@+id/guideline15"
            app:layout_constraintEnd_toStartOf="@+id/guideline22"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="@+id/guideline18"
            app:layout_constraintTop_toTopOf="@+id/guideline14"
            app:layout_constraintVertical_bias="0.48"
            tools:ignore="VisualLintButtonSize" />

        <Button
            android:id="@+id/btn_red_add3"
            style="@style/Widget.AppCompat.Button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:background="#FFff0000"
            android:onClick="@{() -> data.redAdd(3)}"
            android:scrollbarThumbHorizontal="@null"
            android:scrollbarThumbVertical="@null"
            android:text="@string/text_add3"
            android:textColor="@color/white"
            android:textColorHighlight="@null"
            android:textColorHint="@null"
            android:textColorLink="@null"
            android:textSize="30sp"
            android:textStyle="bold"
            app:layout_constraintBottom_toTopOf="@+id/guideline16"
            app:layout_constraintEnd_toStartOf="@+id/guideline22"
            app:layout_constraintStart_toStartOf="@+id/guideline18"
            app:layout_constraintTop_toTopOf="@+id/guideline15"
            app:layout_constraintVertical_bias="0.56"
            tools:ignore="VisualLintButtonSize" />

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

5.MainActivity.java

package com.example.mydatabindingtest;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.Toast;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.ViewModelProviders;
import com.example.mydatabindingtest.databinding.ActivityMainBinding;


public class MainActivity extends AppCompatActivity {

     MyViewModel myViewModel;
     ActivityMainBinding binding;
    private long exitTime;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);

        myViewModel = ViewModelProviders.of(this).get(MyViewModel.class);
        binding.setData(myViewModel);
        binding.setLifecycleOwner(this);
    }

    //返回
    @Override
    public void onBackPressed() {

        if ((System.currentTimeMillis() - exitTime) > 2000) {
            Toast.makeText(getApplicationContext(), "再按一次退出程序",
                    Toast.LENGTH_SHORT).show();
            exitTime = System.currentTimeMillis();
        } else {
            super.onBackPressed();
        }


    }

}