16_Android的数据存储_ SharedPreference、XML和JSON

1. Android读写首选项

1.1 SharedPreferences

　　SharedPreferences 是一种轻型的数据存储方式，它的本质是基于XML文件存储Key-Value键值对数据，通常用来存储一些简单的配置信息，其存储位置在/data/data/<包名>/shared_prefs目录下。

　　SharedPreferences对象本身只能获取数据而不支持存储和修改，存储修改是通过Editor对象实现。本例程讲解 SharedPreference 数据的读写操作。

 1 package com.example.sharedpreference;

 2

 3 import android.app.Activity;

 4 import android.content.SharedPreferences;

 5 import android.content.SharedPreferences.Editor;

 6 import android.os.Bundle;

 7 import android.view.View;

 8 import android.widget.EditText;

 9 import android.widget.Toast;

10

11 public class MainActivity extends Activity {

12

13     static final String KEY = "MyValue";

14     private EditText et;

15     SharedPreferences preferences;

16     Editor editor;

17

18     @Override

19     protected void onCreate(Bundle savedInstanceState) {

20         super.onCreate(savedInstanceState);

21         setContentView(R.layout.activity_main);

22

23         et = (EditText) findViewById(R.id.et);

24         preferences = getPreferences(Activity.MODE_PRIVATE);

25         editor = preferences.edit();

26

27         findViewById(R.id.btnRead).setOnClickListener(new View.OnClickListener() {

28

29             @Override

30             public void onClick(View v) {

31                 //如果键值对不存在，就会将其改为第二个参数。

32                 String in = preferences.getString(KEY, "当前数值不存在");

33                 Toast.makeText(getApplicationContext(), in, Toast.LENGTH_SHORT).show();

34             }

35         });

36

37         findViewById(R.id.btnWrite).setOnClickListener(new View.OnClickListener() {

38

39             @Override

40             public void onClick(View v) {

41                 editor.putString(KEY, et.getText().toString());

42                 if (editor.commit()) {

43                     Toast.makeText(getApplicationContext(), "写入成功", Toast.LENGTH_SHORT).show();

44                 }

45             }

46         });

47     }

48

49 }

MainActivity

 1 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

 2     xmlns:tools="http://schemas.android.com/tools"

 3     android:id="@+id/container"

 4     android:layout_width="match_parent"

 5     android:layout_height="match_parent"

 6     android:orientation="vertical"

 7     tools:context="com.example.sharedpreference.MainActivity"

 8     tools:ignore="MergeRootFrame" >

 9

10     <EditText

11         android:id="@+id/et"

12         android:layout_width="fill_parent"

13         android:layout_height="wrap_content"

14         android:ems="10" >

15

16         <requestFocus />

17     </EditText>

18

19     <Button

20         android:id="@+id/btnRead"

21         android:layout_width="fill_parent"

22         android:layout_height="wrap_content"

23         android:text="读取数据" />

24

25     <Button

26         android:id="@+id/btnWrite"

27         android:layout_width="fill_parent"

28         android:layout_height="wrap_content"

29         android:text="写入数据" />

30

31 </LinearLayout>

activity_main.xml

1.2 SharedPreference

　　SharedPreference是纯操作，如果需要配合界面的话，则需要额外的开发，PreferenceActivity提供了一种快速创建配置首选项界面的方法，并且自动在后台存储首选项数据。

 1 package com.example.preferenceactivity;

 2

 3 import android.app.Activity;

 4 import android.content.Intent;

 5 import android.os.Bundle;

 6 import android.view.View;

 7

 8 public class MainActivity extends Activity {

 9

10     @Override

11     protected void onCreate(Bundle savedInstanceState) {

12         super.onCreate(savedInstanceState);

13         setContentView(R.layout.activity_main);

14

15         findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {

16

17             @Override

18             public void onClick(View v) {

19                 startActivity(new Intent(getApplicationContext(),

20                         MyPreferenceActivity.class));

21             }

22         });

23     }

24

25 }

MainActivity

 1 package com.example.preferenceactivity;

 2

 3 import android.os.Bundle;

 4 import android.preference.CheckBoxPreference;

 5 import android.preference.EditTextPreference;

 6 import android.preference.ListPreference;

 7 import android.preference.PreferenceActivity;

 8 import android.preference.PreferenceManager;

 9 import android.widget.Toast;

10

11 public class MyPreferenceActivity extends PreferenceActivity{

12

13     //checkboxPreference

14     //listPreference

15     //edittextPreference

16

17     PreferenceManager manager;

18     CheckBoxPreference checkBoxPreference;

19     ListPreference listPreference;

20     EditTextPreference editTextPreference;

21

22     @Override

23     protected void onCreate(Bundle savedInstanceState) {

24         super.onCreate(savedInstanceState);

25         addPreferencesFromResource(R.xml.myprefrence);

26

27         manager = getPreferenceManager();

28         checkBoxPreference = (CheckBoxPreference) manager.findPreference("checkbox");

29         Toast.makeText(getApplicationContext(), "当前的状态为：" + checkBoxPreference.isChecked(), Toast.LENGTH_SHORT).show();

30

31         listPreference = (ListPreference) manager.findPreference("list");

32         Toast.makeText(getApplicationContext(), "当前的状态为：" + listPreference.getValue() + "\n开发环境为：" + listPreference.getEntry(), Toast.LENGTH_SHORT).show();

33

34         editTextPreference = (EditTextPreference) manager.findPreference("text");

35         Toast.makeText(getApplicationContext(), "你输入的内容为：" + editTextPreference.getText(), Toast.LENGTH_SHORT).show();

36     }

37 }

MyPreferenceActivity

 1 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"

 2     xmlns:tools="http://schemas.android.com/tools"

 3     android:id="@+id/container"

 4     android:layout_width="match_parent"

 5     android:layout_height="match_parent"

 6     tools:context="com.example.preferenceactivity.MainActivity"

 7     tools:ignore="MergeRootFrame" >

 8

 9     <Button

10         android:id="@+id/btn"

11         android:layout_width="fill_parent"

12         android:layout_height="wrap_content"

13         android:text="修改首选项" />

14

15 </FrameLayout>

activity_main.xml

 1 <?xml version="1.0" encoding="utf-8"?>

 2 <resources>

 3

 4     <string-array name="entries">

 5         <item>Java</item>

 6         <item>Swift</item>

 7         <item>C#</item>

 8     </string-array>

 9     <string-array name="values">

10         <item>Eclips</item>

11         <item>Xcode</item>

12         <item>Visual Studio</item>

13     </string-array>

14

15 </resources>

mylistpreference.xml（values文件中）

2. SQLite数据库的数据读取和写入

  1 package com.example.usingsqlite;

  2

  3 import android.app.ListActivity;

  4 import android.content.ContentValues;

  5 import android.database.Cursor;

  6 import android.database.sqlite.SQLiteDatabase;

  7 import android.os.Bundle;

  8 import android.support.v4.widget.SimpleCursorAdapter;

  9 import android.view.View;

 10 import android.widget.Button;

 11 import android.widget.EditText;

 12

 13 public class MainActivity extends ListActivity {

 14

 15     private SimpleCursorAdapter adapter;

 16     private EditText etName, etSex;

 17     private Button btnAdd;

 18     private Db db;

 19     private SQLiteDatabase dbRead, dbWrite;

 20

 21     @Override

 22     protected void onCreate(Bundle savedInstanceState) {

 23         super.onCreate(savedInstanceState);

 24         setContentView(R.layout.activity_main);

 25

 26         etName = (EditText) findViewById(R.id.etName);

 27         etSex = (EditText) findViewById(R.id.etSex);

 28         btnAdd = (Button) findViewById(R.id.btnAdd);

 29

 30         btnAdd.setOnClickListener(new View.OnClickListener() {

 31

 32             @Override

 33             public void onClick(View v) {

 34                 ContentValues cv = new ContentValues();

 35                 cv.put("name", etName.getText().toString());

 36                 cv.put("sex", etSex.getText().toString());

 37

 38                 dbWrite.insert("user", null, cv);

 39                 refreshListView();

 40             }

 41         });

 42

 43         // getListView().setOnItemLongClickListener(new

 44         // OnItemLongClickListener() {

 45         //

 46         // @Override

 47         // public boolean onItemLongClick(AdapterView<?> parent, View view,

 48         // final int position, long id) {

 49         //

 50         // Cursor c = adapter.getCursor();

 51         // c.moveToPosition(position);

 52         //

 53         // //在数据库中的ID

 54         // int itemId = c.getInt(c.getColumnIndex("_id"));

 55         // dbWrite.delete("user", "_id=?", new String[]{itemId+""});

 56         // refreshListView();

 57         //

 58         //

 59         // // new

 60         // AlertDialog.Builder(MainActivity.this).setTitle("提醒").setMessage("您确定要删除该项吗？").setNegativeButton("取消",

 61         // null).setPositiveButton("确定", new DialogInterface.OnClickListener() {

 62         // //

 63         // // @Override

 64         // // public void onClick(DialogInterface dialog, int which) {

 65         // //

 66         // // }

 67         // // }).show();

 68         //

 69         //

 70         // return true;

 71         // }

 72         // });

 73

 74         Db db = new Db(this);

 75         dbRead = db.getReadableDatabase();

 76         dbWrite = db.getWritableDatabase();

 77

 78         adapter = new SimpleCursorAdapter(this, R.layout.user_list_cell, null,

 79                 new String[] { "name", "sex" }, new int[] { R.id.tvName,

 80                         R.id.tvSex });

 81         setListAdapter(adapter);

 82

 83         refreshListView();

 84

 85         // Db db = new Db(this);

 86         // //写入几条元素

 87         // SQLiteDatabase dbWrite = db.getWritableDatabase();

 88         // ContentValues cv = new ContentValues();

 89         // cv.put("name", "小张");

 90         // cv.put("sex", "男");

 91         // dbWrite.insert("user", null, cv);

 92         //

 93         // cv = new ContentValues();

 94         // cv.put("name", "小红");

 95         // cv.put("sex", "女");

 96         // dbWrite.insert("user", null, cv);

 97         // dbWrite.close();

 98         //

 99         // SQLiteDatabase dbRead = db.getReadableDatabase();

100         // Cursor c = dbRead.query("user", null, null, null, null,null, null);

101         //

102         // while (c.moveToNext()) {

103         // String name = c.getString(c.getColumnIndex("name"));

104         // String sex = c.getString(c.getColumnIndex("sex"));

105         // System.out.println(String.format("name = %s  sex = %s", name, sex));

106         // }

107     }

108

109     private void refreshListView() {

110         Cursor c = dbRead.query("user", null, null, null, null, null, null);

111         adapter.changeCursor(c);

112     }

113

114 }

MainActivity

 1 package com.example.usingsqlite;

 2

 3 import android.content.Context;

 4 import android.database.sqlite.SQLiteDatabase;

 5 import android.database.sqlite.SQLiteOpenHelper;

 6

 7 public class Db extends SQLiteOpenHelper {

 8

 9     public Db(Context context) {

10         // 第四个变量是版本，onUpgrade

11         super(context, "db", null, 1);

12

13     }

14

15     @Override

16     public void onCreate(SQLiteDatabase db) {

17         // 创建了一个用户表

18         db.execSQL("CREAT TABLE user("

19                 + "_id INTEGER PRIMARY KEY AUTOINCREMENT,"

20                 + "name TEXT DEFAULT \"\"," + "sex TEXT DEFAULT \"\")");

21     }

22

23     @Override

24     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

25         // TODO Auto-generated method stub

26

27     }

28

29 }

3. 操作XML数据

　　XML，即可扩展标记语言（Extensible Markup Language），标准通用标记语言的子集，一种用于标记电子文件使其具有结构性的标记语言。它可以用来标记数据、定义数据类型，是一种允许用户对自己的标记语言进行定义的源语言。

3.1 读取与解析XML数据

　　使用Android平台自带的API加载XML数据，并且按照XML的结构将所有数据解析出来。

 1 package com.example.textxml;

 2

 3 import java.io.IOException;

 4 import javax.xml.parsers.DocumentBuilder;

 5 import javax.xml.parsers.DocumentBuilderFactory;

 6 import javax.xml.parsers.ParserConfigurationException;

 7 import org.w3c.dom.Document;

 8 import org.w3c.dom.Element;

 9 import org.w3c.dom.NodeList;

10 import org.xml.sax.SAXException;

11

12 import android.app.Activity;

13 import android.os.Bundle;

14 import android.widget.TextView;

15

16 public class MainActivity extends Activity {

17

18     TextView text;

19

20     @Override

21     protected void onCreate(Bundle savedInstanceState) {

22         super.onCreate(savedInstanceState);

23         setContentView(R.layout.activity_main);

24         text = (TextView) findViewById(R.id.text);

25

26         try {

27

28             DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();

29             DocumentBuilder builder = builderFactory.newDocumentBuilder();

30             Document document = builder.parse(getAssets().open("languages.xml"));

31             //获取根元素

32             Element element = document.getDocumentElement();

33             NodeList list = element.getElementsByTagName("lan");

34             for (int i = 0; i < list.getLength(); i++) {

35                 Element lan = (Element) list.item(i);

36                 text.append(lan.getAttribute("id") + "\n");

37                 text.append(lan.getElementsByTagName("name").item(0).getTextContent() + "\n");

38                 text.append(lan.getElementsByTagName("ide").item(0).getTextContent() + "\n");

39             }

40

41         } catch (ParserConfigurationException e) {

42             e.printStackTrace();

43         } catch (SAXException e) {

44             // TODO Auto-generated catch block

45             e.printStackTrace();

46         } catch (IOException e) {

47             // TODO Auto-generated catch block

48             e.printStackTrace();

49         }

50     }

51 }

MainActivity

 1 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"

 2     xmlns:tools="http://schemas.android.com/tools"

 3     android:id="@+id/container"

 4     android:layout_width="match_parent"

 5     android:layout_height="match_parent"

 6     tools:context="com.example.textxml.MainActivity"

 7     tools:ignore="MergeRootFrame" >

 8

 9     <TextView

10         android:id="@+id/text"

11         android:layout_width="fill_parent"

12         android:layout_height="fill_parent"

13         android:text="ready" />

14

15 </FrameLayout>

activity_main.xml

　　assets文件夹中的languages.xml文件的内容：

 1 <?xml version="1.0" encoding="UTF-8"?>

 2 <Languages cat="it">

 3     <lan id="1">

 4         <name>Java</name>

 5         <ide>Eclipse</ide>

 6     </lan>

 7     <lan id="2">

 8         <name>Swift</name>

 9         <ide>Xcode</ide>

10     </lan>

11     <lan id="3">

12         <name>C#</name>

13         <ide>Visual Studio</ide>

14     </lan>

15 </Languages>

language.xml

3.2 生成与输出XML数据

　　使用Android平台自带的API创建符合XML规范的数据，并且将XML数据输出。

 1 package com.example.textxml;

 2

 3 import java.io.StringWriter;

 4

 5 import javax.xml.parsers.DocumentBuilder;

 6 import javax.xml.parsers.DocumentBuilderFactory;

 7 import javax.xml.parsers.ParserConfigurationException;

 8 import javax.xml.transform.Transformer;

 9 import javax.xml.transform.TransformerConfigurationException;

10 import javax.xml.transform.TransformerException;

11 import javax.xml.transform.TransformerFactory;

12 import javax.xml.transform.dom.DOMSource;

13 import javax.xml.transform.stream.StreamResult;

14

15 import org.w3c.dom.Document;

16 import org.w3c.dom.Element;

17 import android.app.Activity;

18 import android.os.Bundle;

19 import android.widget.TextView;

20

21 public class MainActivity extends Activity {

22

23     TextView text;

24

25     @Override

26     protected void onCreate(Bundle savedInstanceState) {

27         super.onCreate(savedInstanceState);

28         setContentView(R.layout.activity_main);

29         text = (TextView) findViewById(R.id.text);

30

31         try {

32

33             DocumentBuilderFactory builderFactory = DocumentBuilderFactory

34                     .newInstance();

35             DocumentBuilder builder = builderFactory.newDocumentBuilder();

36             // Document document =

37             // builder.parse(getAssets().open("languages.xml"));

38             // //获取根元素

39             // Element element = document.getDocumentElement();

40             // NodeList list = element.getElementsByTagName("lan");

41             // for (int i = 0; i < list.getLength(); i++) {

42             // Element lan = (Element) list.item(i);

43             // text.append(lan.getAttribute("id") + "\n");

44             // text.append(lan.getElementsByTagName("name").item(0).getTextContent() + "\n");

45             // text.append(lan.getElementsByTagName("ide").item(0).getTextContent() + "\n");

46             // }

47

48             Document newxml = builder.newDocument();

49             Element languages = newxml.createElement("Languages");

50             languages.setAttribute("cat", "it");

51

52             Element lan1 = newxml.createElement("lan");

53             lan1.setAttribute("id", "1");

54             Element name1 = newxml.createElement("name");

55             name1.setTextContent("Java");

56             Element ide1 = newxml.createElement("ide");

57             name1.setTextContent("Eclipse");

58             lan1.appendChild(name1);

59             lan1.appendChild(ide1);

60             languages.appendChild(lan1);

61

62             Element lan2 = newxml.createElement("lan");

63             lan2.setAttribute("id", "2");

64             Element name2 = newxml.createElement("name");

65             name1.setTextContent("Swift");

66             Element ide2 = newxml.createElement("ide");

67             name1.setTextContent("Xcode");

68             lan1.appendChild(name2);

69             lan1.appendChild(ide2);

70             languages.appendChild(lan2);

71

72             newxml.appendChild(languages);

73

74             TransformerFactory transformerFactory = TransformerFactory

75                     .newInstance();

76             Transformer transformer = transformerFactory.newTransformer();

77             transformer.setOutputProperty("encoding", "UTF-8");

78             StringWriter sw = new StringWriter();

79             transformer.transform(new DOMSource(newxml), new StreamResult(sw));

80

81             text.setText(sw.toString());

82

83         } catch (ParserConfigurationException e) {

84             e.printStackTrace();

85         } catch (TransformerConfigurationException e) {

86             // TODO Auto-generated catch block

87             e.printStackTrace();

88         } catch (TransformerException e) {

89             // TODO Auto-generated catch block

90             e.printStackTrace();

91         }

92     }

93 }

MainActivity

4. 操作JSON数据

　　JSON：JavaScript 对象表示法（JavaScript Object Notation）。独立于语言和平台，比 XML 更小、更快，更易解析。

4.1 JSON(JavaScript Object Notation) 定义：

　　一种轻量级的数据交换格式，具有良好的可读和便于快速编写的特性。业内主流技术为其提供了完整的解决方案（有点类似于正则表达式，获得了当今大部分语言的支持），从而可以在不同平台间进行数据交换。JSON采用兼容性很高的文本格式，同时也具备类似于C语言体系的行为。– Json.org

4.2 JSON的结构：

　　(1) Name/Value Pairs（无序的）：类似所熟知的Keyed list、 Hash table、Disctionary和Associative array。在Android平台中同时存在另外一个类 "Bundle"，某种程度上具有相似的行为。

　　(2) Array（有序的）：一组有序的数据列表。

　　对象是一个无序的Name/Value Pairs集合。{ name:value , name:value , name:value .... }

　　例子：{ "name":"小猪","age":20 }

4.3读取JSON格式数据

　　Android平台自带了JSON解析的相关API，可以将文件、输入流中的数据转化为JSON对象，然后从对象中获取JSON保存的数据内容。下图是logcat中的内容。

 1 package com.example.testjson;

 2

 3 import java.io.BufferedReader;

 4 import java.io.IOException;

 5 import java.io.InputStreamReader;

 6 import java.io.UnsupportedEncodingException;

 7

 8 import org.json.JSONArray;

 9 import org.json.JSONException;

10 import org.json.JSONObject;

11

12 import android.app.Activity;

13 import android.os.Bundle;

14

15 public class MainActivity extends Activity {

16

17     @Override

18     protected void onCreate(Bundle savedInstanceState) {

19         super.onCreate(savedInstanceState);

20         setContentView(R.layout.activity_main);

21

22         try {

23             InputStreamReader isr = new InputStreamReader(getAssets().open(

24                     "test.json"), "UTF-8");

25             BufferedReader br = new BufferedReader(isr);

26             String line;

27             StringBuilder builder = new StringBuilder();

28             while ((line = br.readLine()) != null) {

29                 builder.append(line);

30             }

31             br.close();

32             isr.close();

33             JSONObject root = new JSONObject(builder.toString());

34             System.out.println("cat=" + root.getString("cat"));

35             JSONArray array = root.getJSONArray("languages");

36             for (int i = 0; i < array.length(); i++) {

37                 JSONObject lan = array.getJSONObject(i);

38                 System.out.println("-----------------------");

39                 System.out.println("id=" + lan.getInt("id"));

40                 System.out.println("name=" + lan.getString("name"));

41                 System.out.println("ide=" + lan.getString("ide"));

42             }

43

44         } catch (UnsupportedEncodingException e) {

45             e.printStackTrace();

46         } catch (IOException e) {

47             e.printStackTrace();

48         } catch (JSONException e) {

49             e.printStackTrace();

50         }

51

52     }

53

54 }

MainActivity

　　assets文件夹中test.json文件的内容：

1 {

2     "languages":[

3         {"id":1,"ide":"Eclipse","name":"Java"},

4         {"id":2,"ide":"Xcode","name":"Swift"},

5         {"id":3,"ide":"Visual Studio","name":"C#"}

6     ],

7     "cat":"it"

8 }

test.json

4.4创建JSON格式数据

　　Android平台自带了JSON构造的相关API，可以轻松地构造JSON对象、JSON数组，并且为他们赋值，而且很容易将JSON对象转换为字符串用于传播。

 1 package com.example.testjson;

 2

 3 import org.json.JSONArray;

 4 import org.json.JSONException;

 5 import org.json.JSONObject;

 6

 7 import android.app.Activity;

 8 import android.os.Bundle;

 9

10 public class MainActivity extends Activity {

11

12     @Override

13     protected void onCreate(Bundle savedInstanceState) {

14         super.onCreate(savedInstanceState);

15         setContentView(R.layout.activity_main);

16

17 //        try {

18 //            InputStreamReader isr = new InputStreamReader(getAssets().open(

19 //                    "test.json"), "UTF-8");

20 //            BufferedReader br = new BufferedReader(isr);

21 //            String line;

22 //            StringBuilder builder = new StringBuilder();

23 //            while ((line = br.readLine()) != null) {

24 //                builder.append(line);

25 //            }

26 //            br.close();

27 //            isr.close();

28 //            JSONObject root = new JSONObject(builder.toString());

29 //            System.out.println("cat=" + root.getString("cat"));

30 //            JSONArray array = root.getJSONArray("languages");

31 //            for (int i = 0; i < array.length(); i++) {

32 //                JSONObject lan = array.getJSONObject(i);

33 //                System.out.println("-----------------------");

34 //                System.out.println("id=" + lan.getInt("id"));

35 //                System.out.println("name=" + lan.getString("name"));

36 //                System.out.println("ide=" + lan.getString("ide"));

37 //            }

38 //

39 //        } catch (UnsupportedEncodingException e) {

40 //            e.printStackTrace();

41 //        } catch (IOException e) {

42 //            e.printStackTrace();

43 //        } catch (JSONException e) {

44 //            e.printStackTrace();

45 //        }

46

47 try {

48

49             JSONObject root = new JSONObject();

50             root.put("cat", "it");

51

52             //{"id":1,"ide":"Eclipse","name":"Java"},

53             JSONObject lan1 = new JSONObject();

54             lan1.put("id", 1);

55             lan1.put("ide", "Eclipse");

56             lan1.put("name", "Java");

57

58             //{"id":2,"ide":"Xcode","name":"Swift"},

59             JSONObject lan2 = new JSONObject();

60             lan2.put("id", 2);

61             lan2.put("ide", "Xcode");

62             lan2.put("name", "Swift");

63

64             //{"id":3,"ide":"Visual Studio","name":"C#"}

65             JSONObject lan3 = new JSONObject();

66             lan3.put("id", 3);

67             lan3.put("ide", "Visual Studio");

68             lan3.put("name", "C#");

69

70             JSONArray array = new JSONArray();

71             array.put(lan1);

72             array.put(lan2);

73             array.put(lan3);

74

75             root.put("languages", array);

76

77             System.out.println(root.toString());

78

79         } catch (JSONException e) {

80             // TODO Auto-generated catch block

81             e.printStackTrace();

82         }

83

84     }

85

86 }

MainActivity

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16_Android的数据存储_ SharedPreference、XML和JSON

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