要实现关机后数据也不会丢失，需要使用到
AndroidViewModel,SaveStateHandle 和 SharePreferences
要达到的目的就是将数据保存成这个亚子

就不会出现app在异常闪退或者关机后数据的丢失了

数据类

package com.example.applicationtest04;

import android.app.Application;
import android.content.Context;
import android.content.SharedPreferences;

import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.SavedStateHandle;

public class MyVIewModel extends AndroidViewModel {
    SavedStateHandle handle; //声明savedstatehandle 类型
    String shpName = getApplication().getResources().getString(R.string.shp_name);
    String key = getApplication().getResources().getString(R.string.key);
    public MyVIewModel(@NonNull Application application, SavedStateHandle handle) {
        super(application);
        this.handle = handle;
        if(!handle.contains(key)){
            load();
        }
    }
    public LiveData<Integer> getNumber(){
        return handle.getLiveData(key);
    }
    public void load(){
        SharedPreferences shp = getApplication().getSharedPreferences(shpName, Context.MODE_PRIVATE);
        int x = shp.getInt(key,0);
        handle.set(key,x);

    }
    public void save(){
        SharedPreferences shp = getApplication().getSharedPreferences(shpName,Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = shp.edit();
        editor.putInt(key,getNumber().getValue());
        editor.apply();
    }
    public void add(int x){
        handle.set(key,getNumber().getValue()+x);
    }
}
//这段代码里面有几个重要的点就是在使用handle的时候要注意使用的数据是liveData

Mainactive类

package com.example.applicationtest04;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.SavedStateVMFactory;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelProviders;

import android.os.Bundle;

import com.example.applicationtest04.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {
    MyVIewModel myVIewModel;
    ActivityMainBinding binding;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);
        this.myVIewModel = ViewModelProviders.of(this,new SavedStateVMFactory(this)).get(MyVIewModel.class);
        binding.setData(myVIewModel);
        binding.setLifecycleOwner(this);
    }

    @Override
    protected void onPause() {
        super.onPause();
        myVIewModel.save();
    }
}
//这段代码的重点就是使用onPause这个声明周期的函数来调用save()函数

布局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="Data"
            type="com.example.applicationtest04.MyVIewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{String.valueOf(Data.getNumber())}"
            android:textColor="@color/colorPrimaryDark"
            android:textSize="36sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintHorizontal_bias="0.497"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.324" />

        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginEnd="8dp"
            android:layout_marginBottom="8dp"
            android:text="@string/buttonPlus"
            android:onClick="@{()->Data.add(1)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.182"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.499" />

        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginEnd="8dp"
            android:layout_marginBottom="8dp"
            android:text="@string/buttonSub"
            android:onClick="@{()->Data.add(-1)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.804"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.499" />

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

测试效果
先加到12

再重启

重启之后重新打开app

值还是没有变化
测试成功