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; //聲明savedstatehandle 類型
 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);
 }
}
//這段代碼里面有幾個重要的點就是在使用handle的時候要注意使用的數(shù)據(jù)是liveData

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();
 }
}
//這段代碼的重點就是使用onPause這個聲明周期的函數(shù)來調(diào)用save()函數(shù)

<?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>