【Android Studio】数据持久化（一）文件存储

Java

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.os.Bundle;
import android.text.TextUtils;
import android.widget.EditText;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity {
    private EditText editText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editText=findViewById(R.id.edit);
        //读取上一次数据
        String oldInput=load();
        if(!TextUtils.isEmpty(oldInput)){
            editText.setText(oldInput);
            //调整光标到最末尾
            editText.setSelection(oldInput.length());
            Toast.makeText(this,"Restoring succeeded",Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        //销毁前保存输入的数据
        String inputText =editText.getText().toString();
        //调用方法保存
        save(inputText);
    }

    public void save(String inputText){
        FileOutputStream out=null;
        BufferedWriter writer=null;
        try{
            //通过openFileOutput得到一个FileOutputStream对象，往文件名称为data写入数据
            out=openFileOutput("data", Context.MODE_PRIVATE);
            //通过BufferedWriter和OutputStreamWriter创建一个BufferedWriter对象
            writer=new BufferedWriter(new OutputStreamWriter(out));
            //通过这个BufferedWriter对象来写入数据
            writer.write(inputText);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if(writer!=null){
                    //关闭writer
                    writer.close();
                }
            }catch (IOException e){
                e.printStackTrace();
            }
        }
    }

    public String load(){
        FileInputStream in=null;
        BufferedReader reader=null;
        //读取到的数据保存在这里
        StringBuilder stringBuilder=new StringBuilder();
        try{
            in=openFileInput("data");
            reader=new BufferedReader(new InputStreamReader(in));
            //以一行为单位进行保存
            String line="";
            //先读一行然后保存在line上，如果line不为空就添加入stringBuilder中
            while ((line=reader.readLine())!=null){
                stringBuilder.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(reader!=null){
                try {
                    reader.close();
                }catch (IOException e){
                    e.printStackTrace();
                }
            }
        }
        return stringBuilder.toString();
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <EditText
        android:id="@+id/edit"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="试着输写什么"/>

</LinearLayout>