public abstract class SQLiteOpenHelper {
	private static final String TAG = SQLiteOpenHelper.class
			.getSimpleName();
	private final Context mContext;
	private final String mName;
	private final CursorFactory mFactory;
	private final int mNewVersion;

	private SQLiteDatabase mDatabase = null;
	private boolean mIsInitializing = false;

	/**
	 * Create a helper object to create, open, and/or manage a database. The
	 * database is not actually created or opened until one of
	 * {@link #getWritableDatabase} or {@link #getReadableDatabase} is called.
	 * 
	 * @param context
	 *            to use to open or create the database
	 * @param name
	 *            of the database file, or null for an in-memory database
	 * @param factory
	 *            to use for creating cursor objects, or null for the default
	 * @param version
	 *            number of the database (starting at 1); if the database is
	 *            older, {@link #onUpgrade} will be used to upgrade the database
	 */
	public SDCardSQLiteOpenHelper(Context context, String name,
			CursorFactory factory, int version) {
		if (version < 1)
			throw new IllegalArgumentException("Version must be >= 1, was "
					+ version);

		mContext = context;
		mName = name;
		mFactory = factory;
		mNewVersion = version;
	}

	/**
	 * Create and/or open a database that will be used for reading and writing.
	 * Once opened successfully, the database is cached, so you can call this
	 * method every time you need to write to the database. Make sure to call
	 * {@link #close} when you no longer need it.
	 * 
	 * <p>
	 * Errors such as bad permissions or a full disk may cause this operation to
	 * fail, but future attempts may succeed if the problem is fixed.
	 * </p>
	 * 
	 * @throws SQLiteException
	 *             if the database cannot be opened for writing
	 * @return a read/write database object valid until {@link #close} is called
	 */
	public synchronized SQLiteDatabase getWritableDatabase() {
		if (mDatabase != null && mDatabase.isOpen() && !mDatabase.isReadOnly()) {
			return mDatabase; // The database is already open for business

		}

		if (mIsInitializing) {
			throw new IllegalStateException(
					"getWritableDatabase called recursively");
		}

		// If we have a read-only database open, someone could be using it

		// (though they shouldn't), which would cause a lock to be held on

		// the file, and our attempts to open the database read-write would

		// fail waiting for the file lock. To prevent that, we acquire the

		// lock on the read-only database, which shuts out other users.

		boolean success = false;
		SQLiteDatabase db = null;
		try {
			mIsInitializing = true;
			if (mName == null) {
				db = SQLiteDatabase.create(null);
			} else {
				String path = getDatabasePath(mName).getPath();
				db = SQLiteDatabase.openOrCreateDatabase(path, mFactory);
			}

			int version = db.getVersion();
			if (version != mNewVersion) {
				db.beginTransaction();
				try {
					if (version == 0) {
						onCreate(db);
					} else {
						onUpgrade(db, version, mNewVersion);
					}
					db.setVersion(mNewVersion);
					db.setTransactionSuccessful();
				} finally {
					db.endTransaction();
				}
			}

			onOpen(db);
			success = true;
			return db;
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			mIsInitializing = false;
			if (success) {
				if (mDatabase != null) {
					try {
						mDatabase.close();
					} catch (Exception e) {
					}
				}
				mDatabase = db;
			} else {
				if (db != null)
					db.close();
			}
		}
		return db;
	}

	/**
	 * Create and/or open a database. This will be the same object returned by
	 * {@link #getWritableDatabase} unless some problem, such as a full disk,
	 * requires the database to be opened read-only. In that case, a read-only
	 * database object will be returned. If the problem is fixed, a future call
	 * to {@link #getWritableDatabase} may succeed, in which case the read-only
	 * database object will be closed and the read/write object will be returned
	 * in the future.
	 * 
	 * @throws SQLiteException
	 *             if the database cannot be opened
	 * @return a database object valid until {@link #getWritableDatabase} or
	 *         {@link #close} is called.
	 */
	public synchronized SQLiteDatabase getReadableDatabase() {
		if (mDatabase != null && mDatabase.isOpen()) {
			return mDatabase; // The database is already open for business

		}

		if (mIsInitializing) {
			throw new IllegalStateException(
					"getReadableDatabase called recursively");
		}

		try {
			return getWritableDatabase();
		} catch (SQLiteException e) {
			if (mName == null)
				throw e; // Can't open a temp database read-only!

			Log.e(TAG, "Couldn't open " + mName
					+ " for writing (will try read-only):", e);
		}

		SQLiteDatabase db = null;
		try {
			mIsInitializing = true;
			String path = getDatabasePath(mName).getPath();
			db = SQLiteDatabase.openDatabase(path, mFactory,
					SQLiteDatabase.OPEN_READWRITE);
			if (db.getVersion() != mNewVersion) {
				throw new SQLiteException(
						"Can't upgrade read-only database from version "
								+ db.getVersion() + " to " + mNewVersion + ": "
								+ path);
			}

			onOpen(db);
			Log.w(TAG, "Opened " + mName + " in read-only mode");
			mDatabase = db;
			return mDatabase;
		} finally {
			mIsInitializing = false;
			if (db != null && db != mDatabase)
				db.close();
		}
	}

	/**
	 * Close any open database object.
	 */
	public synchronized void close() {
		if (mIsInitializing)
			throw new IllegalStateException("Closed during initialization");

		if (mDatabase != null && mDatabase.isOpen()) {
			mDatabase.close();
			mDatabase = null;
		}
	}

	public File getDatabasePath(String name) {
		String EXTERN_PATH = null;
		if (Environment.getExternalStorageState().equals(
				Environment.MEDIA_MOUNTED) == true) {
			String dbPath = mContext.getString(R.string.dir)
					+ mContext.getString(R.string.db_dir) + "/";
			EXTERN_PATH = android.os.Environment.getExternalStorageDirectory()
					.getAbsolutePath() + dbPath;
			File f = new File(EXTERN_PATH);
			if (!f.exists()) {
				f.mkdirs();
			}
		}
		return new File(EXTERN_PATH + name);
	}

	/**
	 * Called when the database is created for the first time. This is where the
	 * creation of tables and the initial population of the tables should
	 * happen.
	 * 
	 * @param db
	 *            The database.
	 */
	public abstract void onCreate(SQLiteDatabase db);

	/**
	 * Called when the database needs to be upgraded. The implementation should
	 * use this method to drop tables, add tables, or do anything else it needs
	 * to upgrade to the new schema version.
	 * 
	 * <p>
	 * The SQLite ALTER TABLE documentation can be found <a
	 * href=http://www.mamicode.com/"http://sqlite.org/lang_altertable.html">here. If you add new>

其实也就是改了一下生成文件的 路径。
将 android sql文件放生成在sd卡