Question

将SQLite数据库写入文本文件时遇到困难。

该应用程序的工作原理是将csv文件导入本地数据库。该数据库用于收集设备上的数据，然后用户将数据导回到csv文件中，以便收集回主Access数据库。

如果导入了csv文件，然后立即导出它就可以正常工作。但是，只要在数据库中创建了新条目，导出就会创建一个空的txt文件。

我认为问题是数据库中的空白值保存为 Null 值，并且将它们写入文本文件存在问题。我只是不确定是否正确的响应是更改集合，以便它将写入空白条目而不是 Null 值，或者是否有写 Null 作为csv文件中的空白值。

供参考，这是我的导出代码。

try {
    Log.d("try", "initiated");
    cursor = db.query("PROD",
            new String[]{"_id", "PUMPER_NO", "WELL_ID", "TANK1_INV", "TANK2_INV", "TANK3_INV", "PROB1", "PROB2", "WATER_RMVD", "OSALE1_IN", "OSALE1_DATE", "OSALE1_TK", "OSALE1_BBL",
                    "OSALE2_IN", "OSALE2_DATE", "OSALE2_TK", "OSALE2_BBL", "GAGED_FLUID", /*"DIFF",*/ "MCFD", "MCF_CUM", "TUBING", "CASING", "LINE", "CYCLES", "CYC_TIME", "CYC_DAYS", "DAYS_OFF",
                    "HRS_PUMPED", "COMMENTS", "MTRIX", "DTF", "TMF", "XTRA1", "XTRA2"},
            null, null, null, null, null);
    int rowcount = 0;
    int colcount = 0;

    Log.d("FileWriter", "initiated");
    File saveFile = new File(Environment.getExternalStorageDirectory() + "/Wellpro/exportprod.txt");
    FileWriter fw = new FileWriter(saveFile, false);

    BufferedWriter bw = new BufferedWriter(fw);
    rowcount = cursor.getCount();
    colcount = cursor.getColumnCount();
    Log.d("Looping", "initiated");
    if (rowcount > 0) {
        cursor.moveToFirst();

        for (int i = 0; i < colcount; i++) {
            if (i != colcount - 1) {
                bw.write(cursor.getColumnName(i) + ",");
            } else {
                bw.write(cursor.getColumnName(i));
            }
        }
        bw.newLine();

        for (int i = 0; i < rowcount; i++) {
            cursor.moveToPosition(i);

            for (int j = 0; j < colcount; j++) {
                if (j != colcount - 1) {
                    bw.write(cursor.getString(j) + ",");
                } else {
                    bw.write(cursor.getString(j));
                }
            }
            bw.newLine();
        }
        bw.flush();
        Toast.makeText(this, "Data Exported", Toast.LENGTH_LONG);
    }
} catch (Exception ex) {
    if (db.isOpen()) {
        db.close();
    }
} finally {
    cursor.close();
    db.close();
}

这是两个条目。没有 Null 值的那个来自原始CSV文件，第二个条目是在程序中创建的那个。在创建第二个条目之前，导出工作正常。

"8" "8" "1255"  "ALESI-OVINGTON #2" "79.0"  "0.0"   "0.0"   ";" ";" "0.0"   ""  ""  ""  ""  ""  ""  ""  ""  "0.0"   "NULL"  "4.68"  "28.08" "0.0"   "0.0"   "60.0"  "0.0"   "0.0"   "0.0"   "0" "0.0"   "Not pumping"   "2.0"   "2016/09/26"    ""  "6" ""  "NULL"  "NULL"

"124"   "124"   "NULL"  "ALESI-OVINGTON #2" "81.0"  "0.0"   "0.0"   "NULL"  "NULL"  "0.0"   "NULL"  "NULL"  "NULL"  "NULL"  "NULL"  "NULL"  "NULL"  "NULL"  "2.0"   "10.0"  "10.47" "227.01"    "0.0"   "0.0"   "60.0"  "0.0"   "0.0"   "0.0"   "0" "0.0"   ""  "NULL"  "2016/10/15"    "NULL"  "NULL"  "NULL"  "1.0"   "1.0"

提前感谢您的帮助！

将空值写入Sqlite的文本文件

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