android 存储结构与存储方法

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1. android的存储方式主要分为：1）本地的文本存储；2）数据库存储
    存储方法：1）SharedPreference 存储：适用于简单的数据保存例如属性文件
                    2）文件存储数据：常用方式，可保存较大数据，可存储在系统或者SD卡中
                    3）SQLite数据库存储：以数据库形式存储数据
                    4）ContentProvider存储数据：为存储和获取提供统一接口，主要用于程序间数据共享
                    5）网络存储：通过网络来存储获取数据，主要应用在网络相关的应用中
2. 文件结构
    1）系统文件：主要存储在\system文件夹下，子文件夹有，app,bin,etc,media等。更改读取等操作需要roots权限
    2）数据文件：主要存储在\data文件夹下，子文件夹有，app,backup,data等，主要存储着应用程序以及应用中产生的临时数据等信息。data文件夹下的没有权限的程序不能相互访问数据，保护私有数据
    3）外部存储：对于较大的文件一般会存储在SD卡等外部存储中。只要有访问SD卡权限就能够访问其中所有文件，数据安全性较低
3. 5种测试方法的实例
     1）SharedPreference 存储：以一个登陆界面来演示
     如下是.xml 和.java 文件代码
     程序中将用户名user 和密码 pass 通过SharedPreference 存储，当再次打开应用时，由initView();方法把上次的配置信息直接显示在界面上
     通过SharedPreferences userinfo = getSharedPreferences("user_info",0);获得SharedPreferences对象
     通过userinfo.edit().putString("name",user.getText().toString()).commit();存储数据，利用对象的edit接口的putString方法保存，最终的提交是通过commit()来完成的
     在initView();中可以看到，获取数据是通过SharedPreferences对象userinfo的getString方法实现的。

package com.example.warrior.sharedpreferencetest;

import android.app.Activity;
import android.content.SharedPreferences;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageButton;


public class MainActivity extends Activity {
    private EditText user = null;
    private EditText password = null;
    private ImageButton loginBtn = null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        user = (EditText)findViewById(R.id.user);
        password = (EditText)findViewById(R.id.pass);
        loginBtn = (ImageButton)findViewById(R.id.loginButton);
        initView();
        loginBtn.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
               if(event.getAction()==MotionEvent.ACTION_DOWN){
                   v.setBackgroundResource(R.drawable.b2);
                   SharedPreferences userinfo = getSharedPreferences("user_info",0);
                   userinfo.edit().putString("name",user.getText().toString()).commit();
                   userinfo.edit().putString("pass",password.getText().toString()).commit();
               }
                else if(event.getAction()==MotionEvent.ACTION_UP){
                   v.setBackgroundResource(R.drawable.b3);
               }
                return false;

            }
        });
    }
    private void initView(){
        SharedPreferences userInfo = getSharedPreferences("user_info",0);
        String username = userInfo.getString("name","");
        String pass = userInfo.getString("pass","");
        user.setText(username);
        password.setText(pass);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

<RelativeLayout xmlns:android=" />
    xmlns:tools=" />
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    android:background="@drawable/b1"
    tools:context=".MainActivity">

    <EditText
        android:layout_width="185dp"
        android:layout_height="40dp"
        android:id="@+id/user"
        android:hint="enter your name"
        android:singleLine="true"
        android:layout_alignParentTop="true"
        android:layout_alignLeft="@+id/pass"
        android:layout_marginTop="66dp"
        />
    <EditText
        android:layout_width="185dp"
        android:layout_height="40dp"
        android:id="@+id/pass"
        android:hint="enter your password"
        android:singleLine="true"
        android:layout_below="@+id/user"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="44dp"
        android:inputType="textPassword"
        />
    <ImageButton
        android:layout_width="100dp"
        android:layout_height="60dp"
        android:id="@+id/loginButton"
        android:background="@drawable/ibtn"
        android:layout_centerVertical="true"
        android:layout_alignRight="@+id/pass"
        android:layout_marginRight="20dp"
        />

</RelativeLayout>

    2）文件存储数据：本示例以创建文件，写入内容，读取内容，显示为主线
     写操作-》通过FileOutputStream fWriteStream = openFileOutput(filename,MODE_APPEND);声称文件写入对象，通过fWriteStream.write(buffer);方法写入，然后关闭fWriteStream.close();
    读操作-》通过FileInputStream fInputStream = openFileInput(filename);创建读操作对象，通过fInputStream.read(buffer);方法读取内容，然后fInputStream.close();关闭。

     代码如下
    .xml

<RelativeLayout xmlns:android=" />
    xmlns:tools=" />
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">
<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/text"
    />


</RelativeLayout>

    .java
    

package com.example.warrior.filestreamtest;

import android.app.Activity;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

import java.io.FileInputStream;
import java.io.FileOutputStream;


public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        String fileName = "fileStreamText.txt";
        String fileContent = "welcome to android!!" +"\n\r"+
                "I love it!!";
        String result = "";
        boolean istrue = writeFile(fileName,fileContent);
        if(istrue){
            result += fileName+"create success!!\n\r";
        }else {
            result+= fileName+"create failure!!\n\r";
        }
        result += readFile(fileName);
        TextView textView = (TextView)findViewById(R.id.text);
        textView.setText(result);
    }

    /*write content to new file
    *param filename: name of new file
    * param content:the content to be writen into the file
    * return boolean:true/success write into false/failure write into
     */
    public boolean writeFile(String filename ,String content){
        try {
            FileOutputStream fWriteStream = openFileOutput(filename,MODE_APPEND);
            byte[] buffer = content.getBytes();
            fWriteStream.write(buffer);
            fWriteStream.flush();
            fWriteStream.close();
            return true;
        }catch (Exception e){
            e.printStackTrace();
            return false;
        }
    }
    /*read content from file
    *param filename:filename
    * return String
     */
    public String readFile(String filename){
        String readBuffer = "";
        try {
            FileInputStream fInputStream = openFileInput(filename);
            int len = fInputStream.available();
            byte[] buffer = new byte[len];
            fInputStream.read(buffer);
            fInputStream.close();
            readBuffer = new String(buffer);
        }catch (Exception e){
            e.printStackTrace();
        }
        return readBuffer;
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}