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android下sqlite操作详解  

2011-09-07 16:16:45|  分类: android |  标签: |举报 |字号 订阅

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一、SQLite简介

 

Android平台上,集成了一个嵌入式关系型数据库—SQLiteSQLite3支持 NULLINTEGERREAL(浮点数字)、TEXT(字符串文本)BLOB(二进制对象)数据类型,虽然它支持的类型虽然只有五种,但实际上sqlite3也接受varchar(n)char(n)decimal(p,s) 等数据类型,只不过在运算或保存时会转成对应的五种数据类型。 SQLite最大的特点是你可以保存任何类型的数据到任何字段中,无论这列声明的数据类型是什么。例如:可以在Integer字段中存放字符串,或者在布尔型字段中存放浮点数,或者在字符型字段中存放日期型值。 但有一种情况例外:定义为INTEGER PRIMARY KEY的字段只能存储64位整数, 当向这种字段中保存除整数以外的数据时,将会产生错误。另外, SQLite 在解析CREATE TABLE 语句时,会忽略 CREATE TABLE 语句中跟在字段名后面的数据类型信息。

 

二、SQLiteCURD

      

Android提供了一个名为SQLiteDatabase的类,该类封装了一些操作数据库的API,使用该类可以完成对数据进行添加(Create)、查询(Retrieve)、更新(Update)和删除(Delete)操作(这些操作简称为CRUD)。对SQLiteDatabase的学习,我们应该重点掌握execSQL()rawQuery()方法。 execSQL()方法可以执行insertdeleteupdateCREATE TABLE之类有更改行为的SQL语句; rawQuery()方法可以执行select语句。SQLiteDatabase还专门提供了对应于添加、删除、更新、查询的操作方法: insert()delete()update()query() 。这些方法实际上是给那些不太了解SQL语法的菜鸟使用的,对于熟悉SQL语法的程序员而言,直接使用execSQL()rawQuery()方法执行SQL语句就能完成数据的添加、删除、更新、查询操作。

 

三、SQLite的事务管理

      

使用SQLiteDatabasebeginTransaction()方法可以开启一个事务,程序执行到endTransaction() 方法时会检查事务的标志是否为成功,如果为成功则提交事务,否则回滚事务。当应用需要提交事务,必须在程序执行到endTransaction()方法之前使用setTransactionSuccessful() 方法设置事务的标志为成功,如果不调用setTransactionSuccessful() 方法,默认会回滚事务。

 

三、SQLite创建、更新数据表

      

如果应用使用到了SQLite数据库,在用户初次使用软件时,需要创建应用使用到的数据库表结构及添加一些初始化记录,另外在软件升级的时候,也需要对数据表结构进行更新。在Android系统,为我们提供了一个名为SQLiteOpenHelper的类,该类用于对数据库版本进行管理,该类是一个抽象类,必须继承它才能使用。为了实现对数据库版本进行管理,SQLiteOpenHelper类有两种重要的方法,分别是onCreate(SQLiteDatabase db)onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)

 

当调用SQLiteOpenHelpergetWritableDatabase()或者getReadableDatabase()方法获取用于操作数据库的SQLiteDatabase实例的时候,如果数据库不存在,Android系统会自动生成一个数据库,接着调用onCreate()方法,onCreate()方法在初次生成数据库时才会被调用,在onCreate()方法里可以生成数据库表结构及添加一些应用使用到的初始化数据。onUpgrade()方法在数据库的版本发生变化时会被调用,数据库的版本是由程序员控制的,假设数据库现在的版本是1,由于业务的需要,修改了数据库表的结构,这时候就需要升级软件,升级软件时希望更新用户手机里的数据库表结构,为了实现这一目的,可以把原来的数据库版本设置为2(或其他数值),并且在onUpgrade()方法里面实现表结构的更新。当软件的版本升级次数比较多,这时在onUpgrade()方法里面可以根据原版号和目标版本号进行判断,然后作出相应的表结构及数据更新。

 

getWritableDatabase()getReadableDatabase()方法都可以获取一个用于操作数据库的SQLiteDatabase实例。但getWritableDatabase() 方法以读写方式打开数据库,一旦数据库的磁盘空间满了,数据库就只能读而不能写,倘若使用的是getWritableDatabase() 方法就会出错。getReadableDatabase()方法先以读写方式打开数据库,如果数据库的磁盘空间满了,就会打开失败,当打开失败后会继续尝试以只读方式打开数据库。

 

四、SQLite示例程序

我们编写一个对表(Contacts)进行的操作来演示SQLite的应用。

 

       1.创建Android工程

Project name:AndroidSQLite

       BuildTarget:Android2.1

       Application name:SQLite嵌入式数据库

       Package name:com.changcheng.sqlite

       Create Activity:AndroidSQLite

       Min SDK Version:7

 

       2. Contact实体

packagecom.changcheng.sqlite.entity;

 

publicclassContact {

        privateInteger_id;

        privateStringname;

        privateStringphone;

        

        publicContact() {

                  super();

         }

 

        publicContact(String name, String phone) {

                  this.name= name;

                  this.phone= phone;

         }

 

        publicInteger get_id() {

                  return_id;

         }

 

        publicvoidset_id(Integer id) {

                  _id= id;

         }

 

        publicString getName() {

                  returnname;

         }

 

        publicvoidsetName(String name) {

                  this.name= name;

         }

 

        publicString getPhone() {

                  returnphone;

         }

 

        publicvoidsetPhone(String phone) {

                  this.phone= phone;

         }

 

        @Override

        publicString toString() {

                  return"Contants [id="+_id+", name="+name+", phone="+phone

                                     +"]";

         }

}

 

       3.编写MyOpenHelper

       MyOpenHelper继承自SQLiteOpenHelper类。我们需要创建数据表,必须重写onCreate(更新时重写onUpgrade方法)方法,在这个方法中创建数据表。

packagecom.changcheng.sqlite;

 

importandroid.content.Context;

importandroid.database.sqlite.SQLiteDatabase;

importandroid.database.sqlite.SQLiteOpenHelper;

 

publicclassMyOpenHelperextendsSQLiteOpenHelper {

 

        privatestaticfinalStringname="contants";//数据库名称

        privatestaticfinalintversion= 1;//数据库版本

 

        publicMyOpenHelper(Context context) {

                  /**

                    * CursorFactory指定在执行查询时获得一个游标实例的工厂类。 设置为null,则使用系统默认的工厂类。

                    */

                  super(context,name,null,version);

         }

 

        @Override

        publicvoidonCreate(SQLiteDatabase db) {

                  //创建contacts表,SQL表达式时提供的字段类型和长度仅为提高代码的可读性。

                   db.execSQL("CREATE TABLE IF NOT EXISTS contacts("

                                     +"_id integer primary key autoincrement,"

                                     +"name varchar(20),"+"phone varchar(50))");

         }

 

        @Override

        publicvoidonUpgrade(SQLiteDatabase db,intoldVersion,intnewVersion) {

                  //仅演示用,所以先删除表然后再创建。

                   db.execSQL("DROP TABLE IF EXISTS contacts");

                  this.onCreate(db);

         }

}

 

4.编写ContactsService

       ContactsService类主要实现对业务逻辑和数据库的操作。

packagecom.changcheng.sqlite.service;

 

importjava.util.ArrayList;

importjava.util.List;

importandroid.content.Context;

importandroid.database.Cursor;

importcom.changcheng.sqlite.MyOpenHelper;

importcom.changcheng.sqlite.entity.Contact;

 

publicclassContactsService {

 

        privateMyOpenHelperopenHelper;

 

        publicContactsService(Context context) {

                  this.openHelper=newMyOpenHelper(context);

         }

 

        /**

          *保存

          *

          *@paramcontact

          */

        publicvoidsave(Contact contact) {

                   String sql ="INSERT INTO contacts (name, phone) VALUES (?, ?)";

                   Object[] bindArgs = { contact.getName(), contact.getPhone() };

                  this.openHelper.getWritableDatabase().execSQL(sql, bindArgs);

         }

 

        /**

          *查找

          *

          *@paramid

          *@return

          */

        publicContact find(Integer id) {

                   String sql ="SELECT _id,name, phone FROM contacts WHERE _id=?";

                   String[] selectionArgs = { id +""};

                   Cursor cursor =this.openHelper.getReadableDatabase().rawQuery(sql,

                                     selectionArgs);

                  if(cursor.moveToFirst())

                           returnnewContact(cursor.getInt(0), cursor.getString(1), cursor

                                               .getString(2));

                  returnnull;

         }

 

        /**

          *更新

          *

          *@paramcontact

          */

        publicvoidupdate(Contact contact) {

                   String sql ="UPDATE contacts SET name=?, phone=? WHERE _id=?";

                   Object[] bindArgs = { contact.getName(), contact.getPhone(),

                                     contact.get_id() };

                  this.openHelper.getWritableDatabase().execSQL(sql, bindArgs);

         }

 

        /**

          *删除

          *

          *@paramid

          */

        publicvoiddelete(Integer id) {

                   String sql ="DELETE FROM contacts WHERE _id=?";

                   Object[] bindArgs = { id };

                  this.openHelper.getReadableDatabase().execSQL(sql, bindArgs);

         }

 

        /**

          *获取记录数量

          *

          *@return

          */

        publiclonggetCount() {

                   String sql ="SELECT count(*) FROM contacts";

                   Cursor cursor =this.openHelper.getReadableDatabase().rawQuery(sql,

                                    null);

                   cursor.moveToFirst();

                  returncursor.getLong(0);

         }

 

        /**

          *获取分页数据

          *

          *@paramstartIndex

          *@parammaxCount

          *@return

          */

        publicList<Contact> getScrollData(longstartIndex,longmaxCount) {

                   String sql ="SELECT _id,name,phone FROM contacts LIMIT ?,?";

                   String[] selectionArgs = { String.valueOf(startIndex),

                                     String.valueOf(maxCount) };

                   Cursor cursor =this.openHelper.getReadableDatabase().rawQuery(sql,

                                     selectionArgs);

                   List<Contact> contacts =newArrayList<Contact>();

                  while(cursor.moveToNext()) {

                            Contact contact =newContact(cursor.getInt(0),

                                               cursor.getString(1), cursor.getString(2));

                            contacts.add(contact);

                   }

                  returncontacts;

         }

 

        /**

          *获取分页数据,提供给SimpleCursorAdapter使用。

          *

          *@paramstartIndex

          *@parammaxCount

          *@return

          */

        publicCursor getScrollDataCursor(longstartIndex,longmaxCount) {

                   String sql ="SELECT _id,name,phone FROM contacts LIMIT ?,?";

                   String[] selectionArgs = { String.valueOf(startIndex),

                                     String.valueOf(maxCount) };

                   Cursor cursor =this.openHelper.getReadableDatabase().rawQuery(sql,

                                     selectionArgs);

                  returncursor;

         }

}

 

       5.编写测试类

      编写一个针对ContactsService的测试类,测试ContactsService类中的各个方法是否正确。

packagecom.changcheng.sqlite.test;

 

importjava.util.List;

importcom.changcheng.sqlite.MyOpenHelper;

importcom.changcheng.sqlite.entity.Contact;

importcom.changcheng.sqlite.service.ContactsService;

importandroid.database.Cursor;

importandroid.test.AndroidTestCase;

importandroid.util.Log;

 

publicclassContactsServiceTestextendsAndroidTestCase {

 

        privatestaticfinalStringTAG="ContactsServiceTest";

 

        //测试创建表

        publicvoidtestCreateTable()throwsThrowable {

                   MyOpenHelper openHelper =newMyOpenHelper(this.getContext());

                   openHelper.getWritableDatabase();

         }

 

        //测试save

        publicvoidtestSave()throwsThrowable {

                   ContactsService contactsService =newContactsService(this.getContext());

                   Contact contact1 =newContact(null,"tom","13898679876");

                   Contact contact2 =newContact(null,"lili","13041094909");

                   Contact contact3 =newContact(null,"jack","13504258899");

                   Contact contact4 =newContact(null,"heary","1335789789");

                   contactsService.save(contact1);

                   contactsService.save(contact2);

                   contactsService.save(contact3);

                   contactsService.save(contact4);

         }

 

        //测试find

        publicvoidtestFind()throwsThrowable {

                   ContactsService contactsService =newContactsService(this.getContext());

                   Contact contact = contactsService.find(1);

                   Log.i(TAG, contact.toString());

         }

 

        //测试update

        publicvoidtestUpdate()throwsThrowable {

                   ContactsService contactsService =newContactsService(this.getContext());

                   Contact contact = contactsService.find(1);

                   contact.setPhone("1399889955");

                   contactsService.update(contact);

         }

 

        //测试getCount

        publicvoidtestGetCount()throwsThrowable {

                   ContactsService contactsService =newContactsService(this.getContext());

                   Log.i(TAG, contactsService.getCount() +"");

         }

 

        //测试getScrollData

        publicvoidtestGetScrollData()throwsThrowable {

                   ContactsService contactsService =newContactsService(this.getContext());

                   List<Contact> contacts = contactsService.getScrollData(0, 3);

                   Log.i(TAG, contacts.toString());

         }

        

        //测试getScrollDataCursor

        publicvoidtestGetScrollDataCursor()throwsThrowable {

                   ContactsService contactsService =newContactsService(this.getContext());

                   Cursor cursor = contactsService.getScrollDataCursor(0, 3);

                  while(cursor.moveToNext()) {

                            Contact contact =newContact(cursor.getInt(0),

                                               cursor.getString(1), cursor.getString(2));

                            Log.i(TAG, contact.toString());

                   }

         }

 

}

      启用测试功能,不要忘记在AndroidManifest.xml文件中加入测试环境。为application元素添加一个子元素:<uses-library android:name="android.test.runner"/>,为application元素添加一个兄弟元素:<instrumentation android:name="android.test.InstrumentationTestRunner"     android:targetPackage="com.changcheng.sqlite" android:label="Tests for My App" />

 

       SQLite数据库以单个文件存储,就像微软的Access数据库。有一个查看SQLite数据库文件的工具——SQLite Developer,我们可以使用它来查看数据库。Android将创建的数据库存放在”/data/data/ com.changcheng.sqlite/databases/contacts”,我们将它导出然后使用SQLite Developer打开。

 

       6.分页显示数据

      我们在ContactsService类中,提供了一个获取分页数据的方法。我们将调用它获取的数据,使用ListView组件显示出来。

 

      编辑mail.xml

<?xmlversion="1.0" encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

         android:orientation="vertical" android:layout_width="fill_parent"

         android:layout_height="fill_parent">

        <!-- ListView -->

        <ListViewandroid:layout_width="fill_parent"

                   android:layout_height="fill_parent" android:id="@+id/listView" />

 

</LinearLayout>

 

mail.xml所在目录里添加一个contactitem.xml

<?xmlversion="1.0" encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

         android:layout_width="wrap_content" android:layout_height="wrap_content">

 

        <!-- contact.id -->

        <TextViewandroid:layout_width="30dip" android:layout_height="wrap_content"

                  android:textSize="20sp"android:id="@+id/tv_id" />

 

        <!-- contact.name -->

        <TextViewandroid:layout_width="150dip" android:layout_height="wrap_content"

                  android:textSize="20sp"android:layout_toRightOf="@id/tv_id"

                   android:layout_alignTop="@id/tv_id" android:id="@+id/tv_name" />

 

        <!-- contact.phone -->

        <TextViewandroid:layout_width="150dip" android:layout_height="wrap_content"

                  android:textSize="20sp"android:layout_toRightOf="@id/tv_name"

                   android:layout_alignTop="@id/tv_name" android:id="@+id/tv_phone" />

 

</RelativeLayout>

 

 

      编辑AndroidSQLite类:

packagecom.changcheng.sqlite;

 

importjava.util.ArrayList;

importjava.util.HashMap;

importjava.util.List;

importcom.changcheng.sqlite.R;

importcom.changcheng.sqlite.entity.Contact;

importcom.changcheng.sqlite.service.ContactsService;

importandroid.app.Activity;

importandroid.database.Cursor;

importandroid.os.Bundle;

importandroid.view.View;

importandroid.widget.AdapterView;

importandroid.widget.ListView;

importandroid.widget.SimpleAdapter;

importandroid.widget.Toast;

importandroid.widget.AdapterView.OnItemClickListener;

 

publicclassAndroidSQLiteextendsActivity {

        /** Called when the activity is first created. */

        @Override

        publicvoidonCreate(Bundle savedInstanceState) {

                  super.onCreate(savedInstanceState);

                   setContentView(R.layout.main);

                  //获取分页数据

                   ContactsService contactsService =newContactsService(this);

                   List<Contact> contacts = contactsService.getScrollData(0, 3);

                  //获取ListView

                   ListView lv = (ListView)this.findViewById(R.id.listView);

                  //生成List<? extends Map<String, ?>>数据

                   List<HashMap<String, Object>> data =newArrayList<HashMap<String, Object>>();

                  for(Contact contact : contacts) {

                            HashMap<String, Object> item =newHashMap<String, Object>();

                            item.put("_id", contact.get_id());

                            item.put("name", contact.getName());

                            item.put("phone", contact.getPhone());

                            data.add(item);

                   }

                  //生成Adapter

                   SimpleAdapter adapter =newSimpleAdapter(this, data,

                                     R.layout.contactitem,newString[] {"_id","name","phone"},

                                    newint[] { R.id.tv_id, R.id.tv_name, R.id.tv_phone});

                  //设置ListView适配器

                   lv.setAdapter(adapter);

                  

                  //ListView添加事件

                   lv.setOnItemClickListener(newOnItemClickListener() {

 

                           @Override

                           publicvoidonItemClick(AdapterView<?> parent, View view,

                                              intposition,longid) {

                                     HashMap<String, Object> item = (HashMap<String, Object>) parent

                                                        .getItemAtPosition((int) id);

                                     Toast.makeText(AndroidSQLite.this, item.get("name").toString(),

                                                        1).show();

                            }

 

                   });

         }

}

 

上面编写的分页显示数据比较麻烦,Android为我们提供了一个SimpleCursorAdapter类。使用它可以方便的显示分页数据。将AndroidSQLite类修改为:

      

package com.changcheng.sqlite;

 

import com.changcheng.sqlite.R;

import com.changcheng.sqlite.service.ContactsService;

import android.app.Activity;

import android.database.Cursor;

import android.os.Bundle;

import android.widget.ListView;

import android.widget.SimpleCursorAdapter;

 

public class AndroidSQLite extends Activity {

         /** Called when the activity is first created. */

         @Override

         public void onCreate(Bundle savedInstanceState) {

                   super.onCreate(savedInstanceState);

                   setContentView(R.layout.main);

 

                   // 获取分页数据

                   ContactsService contactsService = new ContactsService(this);

                   Cursor cursor = contactsService.getScrollDataCursor(0, 3);

                   // 获取ListView

                   ListView lv = (ListView) this.findViewById(R.id.listView);

                   // 创建Adapter

                   SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,

                                     R.layout.contactitem, cursor, new String[] { "_id", "name",

                                                        "phone" }, new int[] { R.id.tv_id, R.id.tv_name,

                                                        R.id.tv_phone });

                   // 设置ListView适配器

                   lv.setAdapter(adapter);

 

                   // ListView添加事件

                   lv.setOnItemClickListener(new OnItemClickListener() {

 

                            @Override

                            public void onItemClick(AdapterView<?> parent, View view,

                                               int position, long id) {

                                     Cursor cursor = (Cursor) parent

                                                        .getItemAtPosition((int) position);

                                     Toast.makeText(AndroidSQLite.this, cursor.getString(1), 1)

                                                        .show();

                            }

                   });

         }

}

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