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 }
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>
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 }
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 }
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>
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>
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 }
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 }
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>
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>
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 }
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 }
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 }
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 }