java - 光标!= null 但null？

Question

当应用程序同步时，我尝试更新数据库中每一行的“html”列。我用过这个教程Here将应用程序添加到“配置文件”列表中。这是我在 SyncAdapter 中使用的代码:

private static void performSync(Context context, Account account, Bundle extras, String authority, ContentProviderClient provider, SyncResult syncResult) throws OperationCanceledException {
  MySQLiteHelper openHelperClass;
  SQLiteDatabase sqliteDatabase;
  String str;
  mContentResolver = context.getContentResolver();
  Log.i(TAG, "performSync: " + account.toString());

  Log.v(TAG, "CDS Opened!");
  openHelperClass = new MySQLiteHelper(context);
  sqliteDatabase = openHelperClass.getWritableDatabase();
  Log.v(TAG, "CDS loaded db!");
  Cursor cursor = sqliteDatabase.query("offline", null, null, null, null, null, null);
  Log.v(TAG, "CDS queried!");
  if(cursor != null) {
      Log.v(TAG, "Cursor not null!");
      Log.v(TAG,cursor.toString());
      if(cursor.moveToFirst()) {
          Log.v(TAG, "first pos");
      while(cursor.moveToNext()) {
          Log.v(TAG, "1");
          Log.v(TAG, "Cursor moving!");
          String skolelogg = cursor.getString(cursor.getColumnIndexOrThrow(MySQLiteHelper.COLUMN_SKOLE_LOGGING_OFFLINE));
          int skplid = cursor.getInt(cursor.getColumnIndexOrThrow(MySQLiteHelper.COLUMN_PLAN_ID));
          String skplant = cursor.getString(cursor.getColumnIndexOrThrow(MySQLiteHelper.COLUMN_PLAN_TYPE));
          int offid = cursor.getInt(cursor.getColumnIndexOrThrow(MySQLiteHelper.COLUMN_ID_OFFLINE));
          try {
              HttpClient hc = new DefaultHttpClient();
              HttpPost post = new HttpPost("https://romres.ist-asp.com/WebUntis/Timetable.do?simple=1&type=" + skplant + "&" + skolelogg + "&id="+ Integer.toString(skplid));

              HttpResponse rp = hc.execute(post);
               if(rp.getStatusLine().getStatusCode() == HttpStatus.SC_OK){
                   str = EntityUtils.toString(rp.getEntity());
                   Log.v(TAG, "Syncing....");
                   Log.v(TAG, "Syncing ID: " + Integer.toString(offid));

                   String csstext = "<link rel='stylesheet' type='text/css' href='Styles/webuntis.css'>";
                   csstext += "<style type='text/css'>";
                   csstext += "*.A_0_1 {background:#f49f25;font-size:12px;}";
                   csstext += "*.I_100_28 {background:#ffff80;}";
                   csstext += "*.I_100_29 {background:#ffff80;}";
                   csstext += "*.I_100_30 {background:#ffff80;}";
                   csstext += "*.I_100_31 {background:#ffff80;}";
                   csstext += "*.I_100_368 {background:#ffff80;}";
                   csstext += "*.I_100_710 {background:#ff00ff;}";
                   csstext += "*.A_0_9 td,*.A_0_11 td,*.A_0_12 td,*.A_11_9 td,*.A_11_11 td,*.A_11_12 td,*.A_40_9 td,*.A_40_11 td,*.A_40_12 td,*.A_41_9 td,*.A_41_11 td,*.A_41_12 td,*.A_5_9 td,*.A_5_11 td,*.A_5_12 td,*.A_10_9 td,*.A_10_11 td,*.A_10_12 td,*.A_50_9 td,*.A_50_11 td,*.A_50_12 td,*.A_51_9 td,*.A_51_11 td,*.A_51_12 td,*.A_15_9 td,*.A_15_11 td,*.A_15_12 td,*.A_20_9 td,*.A_20_11 td,*.A_20_12 td {text-decoration: line-through;}";
                   csstext += "</style>";

                   Document doc = Jsoup.parse(str);
                   Element title = doc.select("div.def").first();
                   String s = title.toString();

                   Element offlinetext = doc.append("<div class='offlinetext'>Offline-Timeplan</div>");
                   String offltt = "<div class='offlinetext'>Offline-Timeplan</div>";

                   String extraCSS = "<style>";
                   extraCSS += ".offlinetext {font-family: Arial; font-size: 20px; font-style: normal; font-weight: 500; color: #FF9900; line-height: 19px; height: 30px;}';";
                   extraCSS += "</style>";

                   Element title2 = doc.select("div.pagetitle").first();
                   String s2 = title2.toString();
                   str = csstext + extraCSS + offltt + s2 + s;

                   ContentValues cv = new ContentValues();
                   cv.put(MySQLiteHelper.COLUMN_SKOLE_HTML_CODE, str);
                   sqliteDatabase.update(MySQLiteHelper.TABLE_OFFLINE, cv, "_id = ?", new String [] { Integer.toString(offid) });
               }
          }
          catch(IOException e){
              Log.v(TAG, e.toString());

          }
      }
      }
      else {
          Log.v(TAG, "moveToNext() is false");
      }
  }
  else{
      Log.v(TAG, "It's null");
  }

 }

这是当我在 Android 的设置菜单中按“同步”时的 LogCat 输出:

12-04 21:17:30.066: D/webviewglue(20944): nativeDestroy view: 0x51028af0
12-04 21:17:39.241: I/ContactsSyncAdapterService(21115): performSync: Account {name=*, type=*.account}
12-04 21:17:39.246: V/ContactsSyncAdapterService(21115): CDS Opened!
12-04 21:17:39.251: V/ContactsSyncAdapterService(21115): CDS loaded db!
12-04 21:17:39.251: V/ContactsSyncAdapterService(21115): CDS queried!
12-04 21:17:39.251: V/ContactsSyncAdapterService(21115): Cursor not null!
12-04 21:17:39.256: V/ContactsSyncAdapterService(21115): android.database.sqlite.SQLiteCursor@411c4de0
12-04 21:17:39.256: V/ContactsSyncAdapterService(21115): moveToNext() is false


问题是一切正常，直到到达cursor.moveToFirst()。正如您所看到的，光标同时为 null 和非 null(?)，因为它通过了“cursor != null”检查，但返回了带有 null 的“cursor.moveToFirst”。我真的需要帮助。我不明白出了什么问题。我在编写 SyncAdapter 甚至 ContentProvider 方面仍然是菜鸟。

编辑:我很蠢。正如贾斯汀指出的，游标确实是空的，因为表中没有行。在我向表中添加条目后它就起作用了!

Answer 1

moveToFirst() 返回 false 意味着您的光标为空(没有行)。这不等于 null。