创建一个DataBaseHelper的类，这个类是继承SQLiteOpenHelper类的，这个类中包含创建数据库、打开数据库、创建表、添加数据和查询数据的方法。代码如下：
package com.example.message_board;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import android.R.bool;
import android.R.integer;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DataBaseHelper extends SQLiteOpenHelper
{
private static String DB_PATH= "";
private static String DB_NAME="Message.db";
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;
Log.v("DB_PATH1",DB_PATH);
DB_PATH=myContext.getDatabasePath(DB_NAME).getPath();
Log.v("DB_PATH2",DB_PATH);
}
/**
* 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;
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;
//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 ;
Log.v("myPath",myPath);
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}
//create a table
public void createTable() throws SQLException
{
try
{
myDataBase.execSQL("CREATE TABLE MessageTable (_id INTEGER PRIMARY KEY AUTOINCREMENT,content TEXT);");
}
catch (Exception e)
{
// TODO: handle exception
}
}
//insert the data to the database
public void insertrecord(String contentString) throws SQLException
{
try
{
//String content=contentString;
String sql="insert into MessageTable(content) values(‘"+contentString+"‘);";
Log.v("aaa", sql);
myDataBase.execSQL(sql);
Log.v("aaa_a", sql);
}
catch (Exception e)
{
Log.v("aaa_e", e.toString());
}
}
//select record
public List<String> selectrecord() throws SQLException
{
List<String> list = new ArrayList<String>();
//String[] strArr = new String[list.size()];
//list.toArray(strArr);
try
{
Cursor cr = myDataBase.rawQuery("select * from MessageTable", null);
while(cr.moveToNext())
{
//Content+=cr.getString(1);
Log.v("Record",cr.getString(1));
list.add(cr.getString(1));
}
}
catch (Exception e)
{
// TODO: handle exception
Log.v("ERR", e.toString());
}
return list;
}
@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)
{
}
}