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 }
Db
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
时间： 2024-10-07 14:12:03