Android的SQLite----重新認識Android（10）

public class MySQLiteDatabaseHelper {
    private String DBPath = Environment.getExternalStorageDirectory().getAbsolutePath();
    private String DBName = "android_manual.db";//資料庫名稱
    private SQLiteDatabase db;

    /**
     * @作用： 構造方法。目的是建立資料庫檔案、建立SQLiteDatabase例項。
     */
    public MySQLiteDatabaseHelper() {
        getConnection();//呼叫自定義的方法初始化資料庫連線
    }

    /**
     * @return void
     * @作用：獲得一個資料庫連線物件，即SQLiteDatabase物件。
     */
    public void getConnection() {
        db = SQLiteDatabase.openDatabase(DBPath + File.separator + DBName, null, SQLiteDatabase.OPEN_READWRITE);//第二個引數是工廠,固定傳入null
    }

    /**
     * @param sql
     * @param selectionArgs
     * @return Cursor
     * @作用：執行帶佔位符的select語句，查詢資料，返回Cursor
     */
    public Cursor selectCursor(String sql, String[] selectionArgs) {
        return db.rawQuery(sql, selectionArgs);
    }

    /**
     * @param sql
     * @param selectionArgs
     * @return int
     * @作用：執行帶佔位符的select語句，返回結果集的個數
     */
    public int selectCount(String sql, String[] selectionArgs) {
        Cursor cursor = db.rawQuery(sql, selectionArgs);
        int count = cursor.getCount();//結果集有多少條記錄
        cursor.close();
        return count;
    }

    /**
     * @param sql
     * @param bindArgs
     * @return boolean
     * @作用：執行帶佔位符的update、insert、delete語句，更新資料庫，返回true或false
     */
    public boolean updateData(String sql, String[] bindArgs) {
        try {
            db.execSQL(sql, bindArgs);//返回值型別為void
            return true;//沒出現異常,說明insert/update/delete成功
        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
    }

    /**
     * @param sql
     * @param selectionArgs
     * @return List<Map<String, Object>>
     * @作用：執行帶佔位符的select語句，返回多條資料，放進List<Map<String,Object>>集合中。
     */
    public List<Map<String, Object>> selectData(String sql, String[] selectionArgs) {
        List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
        Cursor cursor = db.rawQuery(sql, selectionArgs);
        String[] cols_names = cursor.getColumnNames();//獲取每一個欄位的名字
        while (cursor.moveToNext()) {
            Map<String, Object> map = new HashMap<String, Object>();
            for (int i = 0; i < cols_names.length; i++) {
                String cols_value = cursor.getString(i);//每個下標都按照字串來獲取其欄位值
                map.put(cols_names[i], cols_value);//把每個欄位名和對應的值存到map中
            }
            list.add(map);
        }
        if (cursor != null) {
            cursor.close();
        }
        return list;
    }

    /**
     * 作用：將cursor轉成list集合
     *
     * @param cursor
     * @return List<Map<String, Object>>
     */
    public List<Map<String, Object>> cursorToList(Cursor cursor) {
        List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
        String[] cols_names = cursor.getColumnNames();
        while (cursor.moveToNext()) {
            Map<String, Object> map = new HashMap<String, Object>();
            for (int i = 0; i < cols_names.length; i++) {
                Object cols_value = null;
                switch (cursor.getType(i)) {//獲取指定下標的欄位的資料型別  1:int,  2:float,  3:String,  4:Blob,  0:null
                    case 1://int
                        cols_value = cursor.getInt(cursor.getColumnIndex(cols_names[i]));
                        break;
                    case 2://float
                        cols_value = cursor.getFloat(cursor.getColumnIndex(cols_names[i]));
                        break;
                    case 3://String
                        cols_value = cursor.getString(cursor.getColumnIndex(cols_names[i]));
                        break;
                    case 4://blob
                        cols_value = cursor.getBlob(cursor.getColumnIndex(cols_names[i]));
                        break;
                    default://0:null
                        cols_value = null;
                        break;
                }
                map.put(cols_names[i], cols_value);
            }
            list.add(map);
        }
        if (cursor != null) {
            cursor.close();
        }
        return list;
    }

    public void closeDb() {
        if (db != null) {
            db.close();
        }
    }
}