数据存储方式概述

Android中文件的访问权限

实例

关键代码

◆注意：Java中RandomAccessFile类支持随机访问文件内容，通过seek（）定位文件位置。
FileDemo.zip

MainActivity.java

package com.bluelesson.filedemo;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    public void onClick(View view) {
        int id = view.getId();
        String name = null;
        int mode = 0;
        switch (id){
            case R.id.btn_private:
                name = "private.txt";
                mode = Context.MODE_PRIVATE;
                break;
            case R.id.btn_append:
                name = "append.txt";
                mode = Context.MODE_APPEND;
                break;
            case R.id.btn_global_read:
                name = "global_read.txt";
                mode = Context.MODE_WORLD_READABLE;
                break;
            case R.id.btn_global_write:
                name = "global_write.txt";
                mode = Context.MODE_WORLD_WRITEABLE;
                break;
            case R.id.btn_global_rw:
                name = "global_rw.txt";
                mode = Context.MODE_WORLD_READABLE|Context.MODE_WORLD_WRITEABLE;
                break;
        }
        try {
            FileOutputStream outputStream = openFileOutput(name,mode);
            String content = "这是我的内容";
            outputStream.write(content.getBytes());
            outputStream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <Button
        android:id="@+id/btn_private"
        android:text="私有方式"
        android:textSize="20sp"
        android:onClick="onClick"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <Button
        android:id="@+id/btn_append"
        android:text="追加方式"
        android:textSize="20sp"
        android:onClick="onClick"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <Button
        android:id="@+id/btn_global_read"
        android:text="全局读方式"
        android:textSize="20sp"
        android:onClick="onClick"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <Button
        android:id="@+id/btn_global_write"
        android:text="全局写方式"
        android:textSize="20sp"
        android:onClick="onClick"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <Button
        android:id="@+id/btn_global_rw"
        android:text="全局读写方式"
        android:textSize="20sp"
        android:onClick="onClick"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

数据存储方式3：Shared Preferences

介绍

核心原理

关键代码

main1.xml

<?xml version="1.0" encoding="utf-8"?>
<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/edt1"
        android:hint="请在此输入密码"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <Button
        android:id="@+id/btn_set"
        android:text="保存口令"
        android:textSize="20sp"
        android:onClick="btnClick"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    <Button
        android:id="@+id/btn_get"
        android:text="获取口令"
        android:textSize="20sp"
        android:onClick="btnClick"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

MainActivity.java

package com.bluelesson.filedemo;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main1);
    }   
public void btnClick(View view) {
        int id = view.getId();
        switch(id){
            case R.id.btn_set:
                setPass();
                break;
            case R.id.btn_get:
                getPass();
                break;
        }
    }
    private void getPass() {
        // 1. 获取ShredPreferences对象
        SharedPreferences sp = getSharedPreferences(
                "lock", // xml文件的名称，文件夹：/data/data/<package name>/shared_prefs
                Context.MODE_PRIVATE
        );
        // 2. 获取数据
        String pass = sp.getString("pass","-1");
        if(!pass.equals("-1")){
            Toast.makeText(this,"口令："+pass,Toast.LENGTH_SHORT).show();
        }
    }
    private void setPass() {
        // 1. 获取口令
        EditText editText = findViewById(R.id.edt1);
        String pass = editText.getText().toString();
        // 2. 获取ShredPreferences对象
        SharedPreferences sp = getSharedPreferences(
                "lock", // xml文件的名称，文件夹：/data/data/<package name>/shared_prefs
                Context.MODE_PRIVATE
        );
        // 3. 获取编辑器对象
        SharedPreferences.Editor editor = sp.edit();
        // 4. 压入数据
        editor.putString("pass",pass);
        // 5. 提交保存
        editor.commit();
        // 6. 提示一下
        Toast.makeText(this,"保存完成",Toast.LENGTH_SHORT).show();
    }