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;
 }
}