Android 数据存储与访问

一、文件存储读写

1、创建FilePersistenceTest项目

2、编辑界面

【FilePersistenceTest\app\src\main\res\layout\activity_main.xml】

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Type something here"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

3、

【FilePersistenceTest\app\src\main\java\com\example\filepersistencetest\MainActivity.java】

package com.example.filepersistencetest;

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.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity {
    private EditText edit;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        edit = (EditText) findViewById(R.id.editText);
        //数据读取
        String inputText = load();
        if(!TextUtils.isEmpty(inputText)){
            edit.setText(inputText);
            edit.setSelection(inputText.length());
            Toast.makeText(this,"Restoring succeeded",Toast.LENGTH_SHORT).show();
        }
    }

    protected void onDestroy(){
        super.onDestroy();
        String inputText = edit.getText().toString();
        save(inputText);
    }
    //写入数据
    protected void save(String inputText){
        FileOutputStream out = null;
        BufferedWriter writer = null;
        try{
            out = openFileOutput("data", Context.MODE_PRIVATE);
            writer = new BufferedWriter(new OutputStreamWriter(out));
            writer.write(inputText);
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            try {
                if(writer != null){
                    writer.close();
                }
            }catch (IOException e){
                e.printStackTrace();
            }
        }
    }
    //保存数据
    public String load(){
        FileInputStream in = null;
        BufferedReader reader = null;
        StringBuilder content = new StringBuilder();
        try {
            in = openFileInput("data");
            reader =  new BufferedReader(new InputStreamReader(in));
            String line = "";
            while ((line = reader.readLine()) != null){
                content.append(line);
            }
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            if(reader != null){
                try {
                    reader.close();
                }catch (IOException e){
                    e.printStackTrace();
                }
            }
        }
        return content.toString();
    }
}