如何在lambda表达式的select方法中写入多个语句

本文关键字：语句 方法 select lambda 表达式 | 更新日期: 2023-09-27 18:25:51

在向特定Dictionary添加项目的同时，我正试图使用XDocument准备一个XML文档，但我遇到了以下错误。

无法根据用法推断方法"System.Linq.Enumerable.Select（System.Collections.Generic.IEnumerable，System.Func）"的类型参数。请尝试显式指定类型参数。

代码片段是

Dictionary<string, string> userguid = new Dictionary<string, string>();
    XDocument XMLDoc =
                new XDocument(new XDeclaration("1.0", "utf-8", "yes"),
                new XElement("NewDataSet",
                  new XElement("Users",
                      new XElement("UserID", userid),
                      new XElement("FullName", "anyone"),
                      new XElement("UserName", "anyone"),
                      new XElement("Password", 123),
                      new XElement("Description", "anyone"),
                      new XElement("DomainName", string.Empty),
                      new XElement("Mailbox_Size", 20),
                      new XElement("Enabled", "True"),
                      new XElement("Permissions", 14),
                      new XElement("CreationTime", "2011-07-19T17:45:58.53125+05:30")
                      ),
                userNames.Select((item, value) =>
                   {
                       new XElement("Users",
                          new XElement("UserID", Guid.NewGuid().ToString("N")),
                          new XElement("FullName", item.Trim()),
                          new XElement("UserName", item.Trim()),
                          new XElement("Password", passwords[value].Trim()),
                          new XElement("Description", item.Trim()),
                          new XElement("DomainName", string.Empty),
                          new XElement("Mailbox_Size", 20),
                          new XElement("Enabled", "True"),
                          new XElement("Permissions", 14),
                          new XElement("CreationTime", "2011-07-19T17:45:58.53125+05:30"));
                        userguid.Add(userid, emailAddresses[value].Trim());
                   }
                        )
                      ));

如何在lambda表达式的select方法中写入多个语句

您几乎做对了，但在使用语句块（{…}）时，您需要显式地为return指定一个合适的值，因为Select接受一个返回值的委托。

（记住，缩写的单个表达式lambda:

x => expr(x)

实际上只是完整版本的缩写：

x => { return expr(x); }

)

当您使用块而不是lambda（在select方法中，我的意思是）时，您应该返回结果。我的意思是userNames.Select((item, value) => { /* return the result here... */ });:

Dictionary<string, string> userguid = new Dictionary<string, string>();
XDocument XMLDoc =
    new XDocument(
        new XDeclaration("1.0", "utf-8", "yes"),
        new XElement(
            "NewDataSet",
            new XElement(
                "Users",
                new XElement("UserID", userid),
                new XElement("FullName", "anyone"),
                new XElement("UserName", "anyone"),
                new XElement("Password", 123),
                new XElement("Description", "anyone"),
                new XElement("DomainName", string.Empty),
                new XElement("Mailbox_Size", 20),
                new XElement("Enabled", "True"),
                new XElement("Permissions", 14),
                new XElement("CreationTime", "2011-07-19T17:45:58.53125+05:30")
                ),
            userNames.Select(
                             (item, value) =>{
                                 userguid.Add(userid, emailAddresses[value].Trim());
                                 return new XElement(
                                     "Users",
                                     new XElement("UserID", Guid.NewGuid().ToString("N")),
                                     new XElement("FullName", item.Trim()),
                                     new XElement("UserName", item.Trim()),
                                     new XElement("Password", passwords[value].Trim()),
                                     new XElement("Description", item.Trim()),
                                     new XElement("DomainName", string.Empty),
                                     new XElement("Mailbox_Size", 20),
                                     new XElement("Enabled", "True"),
                                     new XElement("Permissions", 14),
                                     new XElement("CreationTime", "2011-07-19T17:45:58.53125+05:30"));
                             }
                )
            ));
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