Question

ViewBag.StatusMessage =
                message == ManageMessageId.ChangePasswordSuccess ? "Your password has been changed."
                : message == ManageMessageId.SetPasswordSuccess ? "Your password has been set."
                : message == ManageMessageId.SetTwoFactorSuccess ? "Your two-factor authentication provider has been set."
                : message == ManageMessageId.Error ? "An error has occurred."
                : message == ManageMessageId.AddPhoneSuccess ? "Your phone number was added."
                : message == ManageMessageId.RemovePhoneSuccess ? "Your phone number was removed."
                : "";

Answer 1

（列出的代码来自ASP.Net MVC 5应用程序中的脚手架ManageController）

这是conditional operator

的链式使用

虽然使用嵌套的if语句可以实现相同的结果：

if (message == ManageMessageId.ChangePasswordSuccess)
    ViewBag.StatusMessage = "Your password has been changed."
else if (message == ManageMessageId.SetPasswordSuccess)
    ViewBag.StatusMessage = "Your password has been set."
...

或切换声明

switch (message)
   case ManageMessageId.ChangePasswordSuccess:
      ViewBag.StatusMessage = "Your password has been changed.";
      break;
   case ManageMessageId.SetPasswordSuccess:
      ViewBag.StatusMessage = "Your password has been set.";
      break;
    ...

以链式方式使用条件运算符有利于避免重复分配ViewBag.StatusMessage，因为它允许投影必须具有相同类型的结果，因此允许单个赋值。它还不鼓励在if或switch语句中编码的副作用行为。

编辑，其他替代方案

如果排列的数量变得非常大，我会选择Dictionary查找模式将ManageMessageId值映射到要在ManageController的Viewbag中设置的字符串，因为这会减少比较次数以匹配适当的密钥：

private static readonly IDictionary<ManageMessageId, string> _messageDictionary 
= new Dictionary<ManageMessageId, string>
  {
      {ManageMessageId.ChangePasswordSuccess, "Your password has been changed."},
      {ManageMessageId.SetPasswordSuccess, "Your password has been set."},
      // ...
  };

等效映射代码将是简单的（仅使用条件运算符） - ManageMessageId是一个枚举：

public async Task<ActionResult> Index(ManageMessageId? message)
{
   ViewBag.StatusMessage = (message.HasValue)
      ? _messageDictionary[message.Value]
      : "";

以下c＃代码是什么意思（链接条件三元运算符）

1 个答案: