vb.net - 单个 linq 中的多个条件

Question

我正在通过具有多行且每行具有标签的控件进行迭代，并且刚刚实现了以下 linq。我可以将以下查询优化为单个查询吗？

 Dim xCheckTag As String = If((From xTag As Row In Sheet1.Rows Where xTag.Tag = "FtpHeader").ToArray.Length > 0, "FtpHeader", _
                            If((From xTag As Row In Sheet1.Rows Where xTag.Tag = "MailHeader").ToArray.Length > 0, "MailHeader", _
                            If((From xTag As Row In Sheet1.Rows Where xTag.Tag = "GoogleHeader").ToArray.Length > 0, "GoogleHeader", _
                            If((From xTag As Row In Sheet1.Rows Where xTag.Tag = "NetworkHeader").ToArray.Length > 0, "NetworkHeader", String.Empty))))

Answer 1

您可以FirstOrDefault按照Dominic的建议使用，但如果没有匹配的项目，它会返回null而不是返回。String.Empty我会DefaultIfEmpty用来返回正确的默认值：

Dim tags = {"FtpHeader","MailHeader","GoogleHeader","NetworkHeader"}
Dim xCheckTag = tags.Where(Function(tag) Sheet1.Rows.Cast(Of Row)().Any(Function(xTag) xTag.Tag = tag)) _
                    .DefaultIfEmpty(String.Empty) _
                    .First()

Answer 2

FirstOrDefault结合使用Any：

Dim tags = {"FtpHeader","MailHeader","GoogleHeader","NetworkHeader"}
Dim xCheckTag = If(tags.FirstOrDefault(Function(tag) Sheet1.Rows.OfType(Of Row).Any(Function(xTag) xTag.Tag = tag)), String.Empty)