一天一点android知识（持久化技术——文件存储）

数据持久化：将内存中的瞬时数据保存到存储设备中，保证即使在手机或电脑关机的情况下，这些数据仍然不会丢失。这里介绍第一种方式文件存储，这种方式是将数据原封不动地保存到文件当中去，其中重点用到了save和load函数（java又得重新梳理一下，好痛苦）。

MainActivity

package com.example.filepersistencetest;

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
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.edit);
        String inputText =load();
        if(!TextUtils.isEmpty(inputText)){
            edit.setText(inputText);
            edit.setSelection(inputText.length());
            Toast.makeText(this,"Restoring succeeded",Toast.LENGTH_SHORT).show();
        }
    }
    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();
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        String inputText = edit.getText().toString();
        save(inputText);
    }

    public 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();
            }
        }
    }
}



           

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <EditText
        android:id="@+id/edit"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Type something here"/>
</LinearLayout>