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。

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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 MainActivityextends 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(newView.OnTouchListener(){
@Override
public boolean onTouch(View v, MotionEventevent) {
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(Menumenu) {
// 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(MenuItemitem) {
// 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);
}
}

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<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/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

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<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/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

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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 MainActivityextends 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(Menumenu) {
// 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(MenuItemitem) {
// 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);
}
}

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