为什么if有时只能工作？

Question

I have this code in my project for checking the controller and the action in my .cshtml-file: 我的项目中有以下代码，用于检查控制器和.cshtml文件中的操作：

@if (ViewContext.RouteData.Values["controller"] == "Home" && ViewContext.RouteData.Values["action"] == "Index")
{
    //Some html
}

When I open the page at the root ( http://localhost/ ), it shows the given html. 当我从根目录（ http：// localhost / ）打开页面时，它显示给定的html。 But when I open it with the full link ( http://localhost/Home/Index ) it's not showing up. 但是，当我使用完整链接（ http：// localhost / Home / Index ）打开它时，它没有显示出来。

When put the variables in the html of the webpage, they are exactly the same. 将变量放在网页的html中时，它们是完全相同的。

Why isn't this working then? 那为什么不起作用呢？

Answer 1

Answer 回答

Use .Equals("") instead of == . 使用.Equals("")代替== 。

Explanation 说明

ViewContext.RouteData.Values["controller"] is of type object . ViewContext.RouteData.Values["controller"]的类型为object 。 If you want to check the equality of the content, you first need to resolve the underlying type as String . 如果要检查内容的相等性，则首先需要将基础类型解析为String 。 If you use == , then C# doesn't resolve the underlying type before doing the comparison. 如果使用== ，则C＃在进行比较之前不会解析基础类型。 When you use Equals() , C# does resolve the underlying type first. 当您使用Equals() ，C＃会首先解析基础类型。 Here's why C# needs to know the underlying type. 这就是C＃需要知道基础类型的原因。

When you use the == operator, and one of the operands is an object , the check is for reference equality. 当使用==运算符，并且其中一个操作数是object ，检查是否为引用相等。 In your question, it doesn't matter that underlying type is String , because C# doesn't check the underlying type. 在您的问题中，基础类型为String无关紧要，因为C＃不会检查基础类型。 If it did check the underlying type, then the == would work, but it doesn't. 如果确实检查了基础类型，则==将起作用，但不会。 It just checks whether the two references are the same. 它只是检查两个引用是否相同。 See MSDN . 参见MSDN 。

If you really want to use == , then you can tell C# explicitly to use a string comparison. 如果您确实想使用== ，则可以明确告诉C＃使用string比较。

ViewContext.RouteData.Values["controller"].ToString()
(ViewContext.RouteData.Values["controller"] as string)
((string)ViewContext.RouteData.Values["controller"])

It's probably best just to use the Equals(string) method. 最好只使用Equals(string)方法。 C# will figure out on its own that you're working with a String . C＃会自己弄清楚您正在使用String 。 In other words, it does matter that the underlying type is a String , because C# resolves the underlying type before calling any method on an object . 换句话说，基础类型是String确实很重要，因为C＃在调用object任何方法之前先解析基础类型。 And the comparison will be for content not reference equality, because the underlying type is String . 并且比较将针对内容而不是引用相等，因为基础类型为String 。 See MSDN . 参见MSDN 。

Fiddle 小提琴

Here is a Fiddle for you. 这是给您的小提琴。

<!DOCTYPE html>
<html lang="en">
    <head></head>
    <body>
        @ViewContext.RouteData.Values["controller"]
        @ViewContext.RouteData.Values["action"]

        @if (ViewContext.RouteData.Values["controller"].Equals("Home") 
             && ViewContext.RouteData.Values["action"].Equals("Index"))
        {
            <p>True</p>
        }
        else
        {
            <p>False</p>
        }

        @if (ViewContext.RouteData.Values["controller"] == "Home" 
             && ViewContext.RouteData.Values["action"] == "Index")
        {
            <p>True</p>
        }
        else
        {
            <p>False</p>
        }
    </body>
</html>

Answer 2

I suggest revert it like this, in case of null 我建议像这样将其还原为null

@if ("Home".Equals(ViewContext.RouteData.Values["controller"]) && "Index".Equals(ViewContext.RouteData.Values["action"]))
{
    //Some html
}

为什么if有时只能工作？

问题描述

2 个解决方案

解决方案1
2 已采纳 2015-04-07 21:42:48

Answer 回答

Explanation 说明

Fiddle 小提琴

解决方案2
0 2015-04-08 07:08:34

为什么if有时只能工作？

问题描述

2 个解决方案

解决方案1 2 已采纳 2015-04-07 21:42:48

Answer 回答

Explanation 说明

Fiddle 小提琴

解决方案2 0 2015-04-08 07:08:34

解决方案1
2 已采纳 2015-04-07 21:42:48

解决方案2
0 2015-04-08 07:08:34