android SQLiteOpenHelper 对SQLite的操作

public class MyDatabaseAdapter {


private static final String DB_NAME = "mzz.db";
private static final String TABLE_NAME = "user";
private static final String T_ID = "_id";
private static final String T_USERNAME = "username";
private static final String T_PASSWORD = "password";

//数据库版本号
private static final int VERSION = 1;

private static final String CREATE_TABLE = "CREATE TABLE "
+ TABLE_NAME
+ " ( "
+ T_ID
+ " INTEGER PRIMARY KEY , "
+ T_USERNAME
+ " TEXT UNIQUE, "
+ T_PASSWORD
+ " TEXT )";

private Context context = null ;
private SQLiteDatabase sqliteDatabase = null ;
private DatabaseHelper databaseHelper = null ;
private static class DatabaseHelper extends SQLiteOpenHelper {

DatabaseHelper(Context context) {
super(context , DB_NAME , null, VERSION);
}


@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(CREATE_TABLE);
}


@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS notes");
onCreate(db);
}
}

//在创建对象的时候就返回一个sqliteDatabase
public MyDatabaseAdapter(Context context) {
this.context = context;
try {
open();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

//只有通过getWriteableDatabase才得到一个sqliteDatabase
public void open() throws SQLException {
databaseHelper = new DatabaseHelper(context);
sqliteDatabase = databaseHelper.getWritableDatabase();
}

//插入数据，根据ID
public long insertData(String username , String password) {
ContentValues cv = new ContentValues();
cv.put(T_USERNAME, username);
cv.put(T_PASSWORD, password);
return sqliteDatabase.insert(TABLE_NAME, T_ID, cv);
}

/**
* 根据username和password查询数据，只有当两个数据同时存在一条数据时返回true，否则返回false
* @param username
* @param password
* @return
*/
public boolean queryByUnAndPw(String username , String password) {
String sql = "select * from user where username='" + username +"' and password='" + password +"'";
Cursor cur = sqliteDatabase.rawQuery(sql, null);
if(cur != null) {
if(cur.moveToNext()) {
return true;
} else {
return false;
}
} else {
return false;
}
}

//查询表中的所有数据
public Cursor queryAll() {
return sqliteDatabase.query(TABLE_NAME, new String[]{T_ID,T_USERNAME,T_PASSWORD},
null, null, null, null, null);
}
}