android（Android中用文件初始化sqlite数据库） _数据库

宝剑锋从磨砺出，梅花香自苦寒来。这篇文章主要讲述android：Android中用文件初始化sqlite数据库相关的知识，希望能为你提供帮助。
很多时候在应用安装初始化时，需要创建本地数据库，同时为数据库添加数据，之后再从数据库中读取数据。

这里有2个思路
1.先在本地创建一个能支持android使用的sqlite数据库文件,启动时,用现成的sqlite的二进制文件进行直接copy到Android系统的数据库路径
2.可以考虑在第一次启动时,执行数据库初始化的sql文件.

1.在本地准备android能使用的sqlite数据库文件

使用sqlite数据库管理工具,看个人爱好(SQLite Database Browser ,Navicat Premium,)
打开数据库,创建"android_metadata"数据表
Sql代码

CREATE TABLE "android_metadata" ("_id" INTEGER PRIMARY KEY AUTOINCREMENT,"locale" TEXT DEFAULT \'en_US\'); //创建表
INSERT INTO "android_metadata" VALUES (1,\'en_US\'); //插入值

创建其他应用需要的表..此处省略.

2.复制文件到应用中.
把第一步创建的数据库文件复制到应用中的assets文件夹, asserts文件夹的路径如下：

文章图片

然后创建DateBaseHelper extends SQLiteOpenHelper的类文件.
代码如下:
java代码

public class DataBaseHelper extends SQLiteOpenHelper {
//The Android\'s default system path of your application database.
private static String DB_PATH = "/data/data/YOUR_PACKAGE/databases/";
private static String DB_NAME = "myDBName";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DataBaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase()throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
//do nothing - database already exist
} else {
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
* @return true if it exists, false if it doesn\'t
*/
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
//database does\'t exist yet.
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transfering bytestream.
* */
private void copyDataBase()throws IOException {
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[]buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase()throws SQLException {
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if (myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
// Add your public helper methods to access and get content from the database.
// You could return cursors by doing "return myDataBase.query(....)" so it\'d be easy
// to you to create adapters for your views.
}

【android（Android中用文件初始化sqlite数据库）】
3.现在我们可以创建DateBaseHelper的实现操作了.
createDataBase() //创建
openDataBase()//打开只读数据库
记得要更改"YOUR_PACKAGE"为你的应用的包名
如:com.examplename.myapp
大概代码如下:
Java代码