Question

我正在迭代控件，它有多行，每行都有一个标签，只是实现了以下的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

您可以使用FirstOrDefault作为 Dominic 建议，但如果没有匹配项，则会返回null而不是String.Empty。我会使用DefaultIfEmpty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

将FirstOrDefault与Any结合使用：

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)

单个linq中的多重条件

2 个答案: