下面c#代码的含义是什么(链接条件三元操作符)

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应用程序中的支架式ASP.Net)

这是条件算子的一种链式使用。

虽然嵌套的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."
... 

或开关语句

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可以避免ViewBag.StatusMessage的重复赋值，因为它允许对必须是相同类型的结果进行投影，从而允许单个赋值。它还阻止了在if或switch语句中可能出现的副作用行为。

编辑，其他替代品

如果排列的数量变得非常大，我将选择一个Dictionary查找模式来将ManageMessageId值映射到要在ManageController的Viewbag中设置的字符串，因为这将减少比较的数量，以便匹配适当的键：

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."},
      // ...
  };

然后，等效的映射代码将是简单的(只使用一次条件运算符)-- ManageMessageId是一个枚举：

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