数据库操作，,public class

数据库操作，,public class

public class Database {    private static DbOpenHelper mDbHelper;    private static final int DB_VERSION = 1;    private static final String DB_NAME = "pdf.db";    public static void close() {        if(mDbHelper != null) {            mDbHelper.close();            mDbHelper = null;        }    }    public static SQLiteDatabase getDb(Context context) {        DbOpenHelper helper = getDbOpenHelper(context);        return helper.getWritableDatabase();    }    public static void writeMessageToDb(SQLiteDatabase db, String name,             String path) {        ContentValues values = new ContentValues();        values.put(PDF.name.name(), name);        values.put(PDF.path.name(), path);        db.insert(PDF.TABLE_NAME, null, values);    }    public static HashMap<String, String> loadMessageFromDb(SQLiteDatabase db) {        Cursor cursor = db.query(PDF.TABLE_NAME, null, null, null, null, null, null);        HashMap<String, String> result = new HashMap<String, String>();        while(cursor.moveToNext()) {            String name = cursor.getString(cursor.getColumnIndex(PDF.name.name()));            String path = cursor.getString(cursor.getColumnIndex(PDF.path.name()));            result.put(name, path);        }        cursor.close();        return result;    }    private static DbOpenHelper getDbOpenHelper(Context context) {        if(mDbHelper == null)            mDbHelper = new DbOpenHelper(context, DB_NAME, DB_VERSION);        return mDbHelper;    }    private static class DbOpenHelper extends SQLiteOpenHelper {        public DbOpenHelper(Context context, String name, int version) {            super(context, name, null, version);        }        @Override        public void onCreate(SQLiteDatabase db) {            db.execSQL("CREATE TABLE " + PDF.TABLE_NAME + " (" +                    PDF._id.name() + " INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, " +                    PDF.name.name() + " TEXT NOT NULL, " +                     PDF.path.name() + " TEXT NOT NULL, " +                    ");"                    );        }        @Override        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {            dropTables(db);            onCreate(db);        }        private void dropTables(SQLiteDatabase db) {            db.execSQL("DROP TABLE IF EXISTS " + PDF.TABLE_NAME);        }       }    enum PDF {        _id,        name,        path;        static final String TABLE_NAME = "PDF";    }}//该片段来自于http://byrx.net