文件管理器源码分析（三）

//存储favorite数据，到数据库//SQLiteOpenHelper是一个帮助管理数据库和版本的工具类。//通过继承并重载方法，快速实现了我们自己的Favorite表的CRUD。//怎么感觉和FileOperationHelper类似，仍然是CRUD，只不过1个是数据库中的，1个是文件的。public class FavoriteDatabaseHelper extends SQLiteOpenHelper {    //下面6个字段是数据库的名字和版本号、表的名字和3个字段    private final static String DATABASE_NAME = "file_explorer";    private final static int DATABASE_VERSION = 1;    private final static String TABLE_NAME = "favorite";    public final static String FIELD_ID = "_id";    public final static String FIELD_TITLE = "title";    public final static String FIELD_LOCATION = "location";    private boolean firstCreate;    //数据库变化的时候，会通知其它监听器    private FavoriteDatabaseListener mListener;    private static FavoriteDatabaseHelper instance;    public interface FavoriteDatabaseListener {        void onFavoriteDatabaseChanged();    }    //这个构造方法和下面的静态获得实例的方法，不太和谐啊~    //乍一看，以为是单例模式呢，实则不是~    public FavoriteDatabaseHelper(Context context, FavoriteDatabaseListener listener) {        super(context, DATABASE_NAME, null, DATABASE_VERSION);        instance = this;        mListener = listener;    }    //这个地方感觉只是方便存储了一个类的实例，但不能保证这个类只有1个实例    public static FavoriteDatabaseHelper getInstance() {        return instance;    }    //数据库创建，1个sql    @Override    public void onCreate(SQLiteDatabase db) {        String sql = "Create table " + TABLE_NAME + "(" + FIELD_ID + " integer primary key autoincrement,"                + FIELD_TITLE + " text, " + FIELD_LOCATION + " text );";        db.execSQL(sql);        firstCreate = true;    }    //升级的时候，直接删除以前的数据库，如果存在的话    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {        String sql = " DROP TABLE IF EXISTS " + TABLE_NAME;        db.execSQL(sql);        onCreate(db);    }    //是否为第1次创建    public boolean isFirstCreate() {        return firstCreate;    }    //判断1个文件路径是否已经存在，或者说是否是Favorite文件    public boolean isFavorite(String path) {        String selection = FIELD_LOCATION + "=?";        String[] selectionArgs = new String[] {            path        };        SQLiteDatabase db = this.getReadableDatabase();        Cursor cursor = db.query(TABLE_NAME, null, selection, selectionArgs, null, null, null);        if (cursor == null)            return false;        boolean ret = cursor.getCount() > 0;        cursor.close();        return ret;    }    //获得Favorite表的游标    public Cursor query() {        SQLiteDatabase db = this.getReadableDatabase();        Cursor cursor = db.query(TABLE_NAME, null, null, null, null, null, null);        return cursor;    }    //插入一条记录    public long insert(String title, String location) {        if (isFavorite(location))            return -1;        SQLiteDatabase db = this.getWritableDatabase();        long ret = db.insert(TABLE_NAME, null, createValues(title, location));        mListener.onFavoriteDatabaseChanged();        return ret;    }    //根据id，删除一条记录。如果需要，然后通知相关监听器    public void delete(long id, boolean notify) {        SQLiteDatabase db = this.getWritableDatabase();        String where = FIELD_ID + "=?";        String[] whereValue = {            Long.toString(id)        };        db.delete(TABLE_NAME, where, whereValue);        if (notify)            mListener.onFavoriteDatabaseChanged();    }    //根据位置删除1条记录，一定通知相关监听器    public void delete(String location) {        SQLiteDatabase db = this.getWritableDatabase();        String where = FIELD_LOCATION + "=?";        String[] whereValue = {            location        };        db.delete(TABLE_NAME, where, whereValue);        mListener.onFavoriteDatabaseChanged();    }    //更新1条记录    public void update(int id, String title, String location) {        SQLiteDatabase db = this.getWritableDatabase();        String where = FIELD_ID + "=?";        String[] whereValue = {            Integer.toString(id)        };        db.update(TABLE_NAME, createValues(title, location), where, whereValue);        mListener.onFavoriteDatabaseChanged();    }    private ContentValues createValues(String title, String location) {        ContentValues cv = new ContentValues();        cv.put(FIELD_TITLE, title);        cv.put(FIELD_LOCATION, location);        return cv;    }}