我怎样才能安全地循环，直到有没有更多不使用＆QUOT做;占位符＆QUOT;而conditon？ [英] How can I safely loop until there is nothing more to do without using a "placeholder" while conditon?

问题描述

为了调用我的Web API方法，直到返回没有更多的数据（我取它批次，以保持每个结果集小，由于客户端的98-LB-弱者角色（Windows CE的掌上设备）），我用这code：

In order to call my Web API method until no more data is returned (I'm fetching it in batches, to keep each result set small, due to the 98-lb-weakling persona of the client (Windows CE handheld device)), I'm using this code:

while (moreRecordsExist)
{
    redemptionsList.redemptions.Clear();
    string uri = String.Format("http://platypus:28642/api/Redemptions/{0}/{1}", lastIdFetched, RECORDS_TO_FETCH);
    var webRequest = (HttpWebRequest)WebRequest.Create(uri);
    webRequest.Method = "GET";

    using (var webResponse = (HttpWebResponse)webRequest.GetResponse())
    {
        if (webResponse.StatusCode == HttpStatusCode.OK)
        {
            var reader = new StreamReader(webResponse.GetResponseStream());
            string s = reader.ReadToEnd();
            var arr = JsonConvert.DeserializeObject<JArray>(s);
            if (null == arr) break;

            foreach (JObject obj in arr)
            {
                id = obj.Value<int?>("Id") ?? 0;
                var _redemptionId = obj.Value<string>("RedemptionId") ?? "";
                var _redemptionItemId = obj.Value<string>("RedemptionItemId") ?? "";
                var _redemptionName = obj.Value<string>("RedemptionName") ?? "";
                double _redemptionAmount = obj.Value<double?>("RedemptionAmount") ?? 0.0;
                var _redemptionDept = obj.Value<string>("RedemptionDept") ?? "";
                var _redemptionSubdept = obj.Value<string>("RedemptionSubDept") ?? "";

                redemptionsList.redemptions.Add(new HHSUtils.Redemption
                {
                    Id = id,
                    RedemptionId = _redemptionId,
                    RedemptionItemId = _redemptionItemId,
                    RedemptionName = _redemptionName,
                    RedemptionAmount = _redemptionAmount,
                    RedemptionDept = _redemptionDept,
                    RedemptionSubDept = _redemptionSubdept,
                });
            } // foreach
        } // if ((webResponse.StatusCode == HttpStatusCode.OK) && (webResponse.ContentLength > 2))
    } // using HttpWebResponse
    int recordsAdded = LocalDBUtils.BulkInsertRedemptions(redemptionsList.redemptions);
    totalRecordsAdded += recordsAdded;
    //moreRecordsExist = (recordsToFetch > (totalRecordsAdded));
    lastIdFetched = id;
} // while

这工作（如果我检查WebResponse的为null，则用一个NullReferenceException崩溃），但我真的不喜欢我while循环，因为一旦moreRecordsExist分配假它从来没有达到过。所以，我设置了ReSharper的猎狗失去它，看它是否有一个更好的建议，但它只是告诉我，前pression始终为真为线，并建议修复这是改变它，而（真）

This works (if I check webResponse for null, it crashes with a NullReferenceException), but I don't really like my while loop, as it is never reached once moreRecordsExist is assigned false. So, I set the Resharper hounds loose on it to see if it had a better suggestion, but it just tells me, "Expression is always true" for that line, and the suggested "fix" for this is to change it to "while (true)"

我看不出这是多大的改善，虽然。

I fail to see how that is much of an improvement, though.

有没有一种方法，我可以完成同样的事情用一个更合理的结构？

Is there a way I can accomplish the same thing with a more sensible construct?

推荐答案

您打破了以破环语句指派后，立即假到 moreRecordsExist 变量，所以它的价值永远不会在循环的开头假的。你可以做一个变化ReSharper的暗示，摆脱 moreRecordsExist 的变量：

You break out the loop with a break statement immediately after assigning false to moreRecordsExist variable, so its value will never be false in the beginning of the loop. You can make a change as ReSharper suggests and get rid of moreRecordsExist variable:

while (true)
{
    redemptionsList.redemptions.Clear();
    string uri = String.Format("http://platypus:28642/api/Redemptions/{0}/{1}", lastIdFetched, RECORDS_TO_FETCH);
    var webRequest = (HttpWebRequest)WebRequest.Create(uri);
    webRequest.Method = "GET";

    using (var webResponse = (HttpWebResponse)webRequest.GetResponse())
    {
        if (webResponse.StatusCode == HttpStatusCode.OK)
        {
            var reader = new StreamReader(webResponse.GetResponseStream());
            string s = reader.ReadToEnd();
            var arr = JsonConvert.DeserializeObject<JArray>(s);
            if (arr == null) break;

            foreach (JObject obj in arr)
            {
                id = obj.Value<int?>("Id") ?? 0;
                var _redemptionId = obj.Value<string>("RedemptionId") ?? "";
                var _redemptionItemId = obj.Value<string>("RedemptionItemId") ?? "";
                var _redemptionName = obj.Value<string>("RedemptionName") ?? "";
                double _redemptionAmount = obj.Value<double?>("RedemptionAmount") ?? 0.0;
                var _redemptionDept = obj.Value<string>("RedemptionDept") ?? "";
                var _redemptionSubdept = obj.Value<string>("RedemptionSubDept") ?? "";

                redemptionsList.redemptions.Add(new HHSUtils.Redemption
                {
                    Id = id,
                    RedemptionId = _redemptionId,
                    RedemptionItemId = _redemptionItemId,
                    RedemptionName = _redemptionName,
                    RedemptionAmount = _redemptionAmount,
                    RedemptionDept = _redemptionDept,
                    RedemptionSubDept = _redemptionSubdept,
                });
            } // foreach
        } // if ((webResponse.StatusCode == HttpStatusCode.OK) && (webResponse.ContentLength > 2))
    } // using HttpWebResponse
    int recordsAdded = LocalDBUtils.BulkInsertRedemptions(redemptionsList.redemptions);
    totalRecordsAdded += recordsAdded;
    //moreRecordsExist = (recordsToFetch > (totalRecordsAdded));
    lastIdFetched = id;
} // while

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