MVC 3/C# 不能使用已在 if 语句中声明的变量

本文关键字：语句 if 声明 变量 不能 MVC | 更新日期: 2023-09-27 18:36:49

我正在尝试在我的控制器中编写代码，该代码在运行时将创建一堆变量，然后使用具有占位符的模板发送电子邮件以包含变量。但是，它将信息从用户帐户分配给变量，如果用户尚未填写该信息，它将崩溃。作为解决方法，我在 if 语句中声明了它们，这些语句首先检查以确保它们不是 null。但是现在当我尝试将它们传递给电子邮件模板时，它告诉我变量不存在。如果我删除 if 语句，它会再次工作。知道为什么吗？

代码如下...

if (UserContext != null && UserContext.Account != null)
        {
            if (UserContext.UserName != null)
            { string UserName = string.Format(UserContext.UserName); }
            if (UserContext.EmailAddress != null)
            { string EmailAddress = string.Format(UserContext.EmailAddress); }
            if (UserContext.Account.PrimaryContactFirstName != null)
            { string FirstName = string.Format(UserContext.Account.PrimaryContactFirstName); }
            if (UserContext.Account.PrimaryContactLastName != null)
            { string LastName = string.Format(UserContext.Account.PrimaryContactLastName); }
            if (UserContext.Account.PrimaryContactPhoneNumber != null)
            { string PhoneNumber = string.Format(UserContext.Account.PrimaryContactPhoneNumber); }
            if (UserContext.Account.HeadquartersAddressLine1 != null)
            {
                string AddressLine1 = string.Format(UserContext.Account.HeadquartersAddressLine1);
                if (UserContext.Account.HeadquartersAddressLine2 != null)
                { string AddressLine2 = string.Format(UserContext.Account.HeadquartersAddressLine2); }
            }
            if (UserContext.Account.HeadquartersCity != null)
            { string City = string.Format(UserContext.Account.HeadquartersCity); }
            if (UserContext.Account.HeadquartersState != null)
            { string State = string.Format(UserContext.Account.HeadquartersState); }
            if (UserContext.Account.HeadquartersZip != null)
            { string ZipCode = string.Format(UserContext.Account.HeadquartersZip); }
            if (UserContext.Account.Name != null)
            { string Name = string.Format(UserContext.Account.Name); }
            string body = string.Format(Resources.ContactUsLoggedInEmailTemplate, model.FirstName, model.LastName, model.PhoneNumber, model.Email, model.ReasonForContact, model.Message, UserName, EmailAddress, FirstName, LastName, PhoneNumber, AddressLine1, AddressLine2, City, State, ZipCode, Name);
            string subject = string.Format("Web Submit: {0}", model.ReasonForContact);
            EmailHelper.SendEmail("support@website.com", subject, body, true);
        }
        if (UserContext == null)
        {
            string body = string.Format(Resources.ContactUsEmailTemplate, model.FirstName, model.LastName, model.PhoneNumber, model.Email, model.ReasonForContact, model.Message);
            string subject = string.Format("Web Submit: {0}", model.ReasonForContact);
            EmailHelper.SendEmail("support@website.com", subject, body, true);
        }
        return RedirectToAction("ContactConfirmation");

MVC 3/C# 不能使用已在 if 语句中声明的变量

每个变量仅在创建它的块的生存期内存在。 随着每个if块的结束，您可以让它们立即消失。 解决方案是首先声明所有变量，然后根据需要分配值。

这是try/catch块的常见烦恼之一。 以后可能有用的任何内容都需要在try之前声明。 如果构造函数可能引发异常，则它应该位于try块内。

因为您声明的是 If 语句中的变量，所以一旦 If 语句完成，它们就会消失。在顶部声明变量（例如：string body;，在任何if检查之前），然后您应该能够将它们传递到您的电子邮件中。

string UserName;
string EmailAddress;
string FirstName;
....
if (UserContext != null && UserContext.Account != null)
        {
            if (UserContext.UserName != null)
            { UserName = string.Format(UserContext.UserName); }
            if (UserContext.EmailAddress != null)
            { EmailAddress = string.Format(UserContext.EmailAddress); }
            if (UserContext.Account.PrimaryContactFirstName != null)
            { FirstName = string.Format(UserContext.Account.PrimaryContactFirstName); }
            if (UserContext.Account.PrimaryContactLastName != null)
            { LastName = string.Format(UserContext.Account.PrimaryContactLastName); }
            if (UserContext.Account.PrimaryContactPhoneNumber != null)
            { PhoneNumber = string.Format(UserContext.Account.PrimaryContactPhoneNumber); }
            if (UserContext.Account.HeadquartersAddressLine1 != null)
            {
                AddressLine1 = string.Format(UserContext.Account.HeadquartersAddressLine1);
                if (UserContext.Account.HeadquartersAddressLine2 != null)
                { AddressLine2 = string.Format(UserContext.Account.HeadquartersAddressLine2); }
            }
            if (UserContext.Account.HeadquartersCity != null)
            { City = string.Format(UserContext.Account.HeadquartersCity); }
            if (UserContext.Account.HeadquartersState != null)
            { State = string.Format(UserContext.Account.HeadquartersState); }
            if (UserContext.Account.HeadquartersZip != null)
            { ZipCode = string.Format(UserContext.Account.HeadquartersZip); }
            if (UserContext.Account.Name != null)
            { Name = string.Format(UserContext.Account.Name); }
            string body = string.Format(Resources.ContactUsLoggedInEmailTemplate, model.FirstName, model.LastName, model.PhoneNumber, model.Email, model.ReasonForContact, model.Message, UserName, EmailAddress, FirstName, LastName, PhoneNumber, AddressLine1, AddressLine2, City, State, ZipCode, Name);
            string subject = string.Format("Web Submit: {0}", model.ReasonForContact);
            EmailHelper.SendEmail("support@website.com", subject, body, true);
        }
        if (UserContext == null)
        {
            body = string.Format(Resources.ContactUsEmailTemplate, model.FirstName, model.LastName, model.PhoneNumber, model.Email, model.ReasonForContact, model.Message);
            subject = string.Format("Web Submit: {0}", model.ReasonForContact);
            EmailHelper.SendEmail("support@website.com", subject, body, true);
        }
        return RedirectToAction("ContactConfirmation");
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