将变量传递给@Styles.Render 函数 [英] Passing variable into @Styles.Render function

问题描述

使用 razor，渲染一组特定的样式表是通过以下方式完成的:

With razor, rendering a specific bundle of stylesheets is done with:

@Styles.Render("~/Content/css")

这指的是 BundleConfig 文件，其中包含以下行:

This refers to the BundleConfig file which has the line:

bundles.Add(new StyleBundle("~/Content/css").Include("~/Content/site.css"));

... 指向 site.css 文件，位于 Content 文件夹内.

... pointing to the site.css file, inside the Content folder.

我想像这样设置一个变量(我试过一个会话变量):

I wanted to set a variable (I've tried a session variable) like this:

Session["cssTheme"] = "~/Content/css";

所以我可以把它放在 Styles.Render 函数中，像这样:

So I could put it in the Styles.Render function, something like this:

@Styles.Render(@Session["cssTheme"])

但它得到无效参数的错误.

But it gets an error of invalid arguments.

我想这样做是为了我可以更改会话变量值(到另一个样式包)，从而更改我的 Web 应用程序的 css 样式.

I wanted to do this so I could change the session variable value (to another style bundle) and that way change the css style of my web application.

那么，如何将编辑过的变量传递给 Styles.Render 函数?

So, how can I pass an edited variable into the Styles.Render function?

推荐答案

首先，Session 是动态的，这意味着它可以容纳任何类型.当您只提取一个值时，它在技术上属于 object 类型.Styles.Render 需要一个 string 类型的参数，因此您需要先将该值转换为 string:

First, Session is dynamic, meaning it can hold any type inside. When you just pull out a value, it's technically of type object. Styles.Render expects a parameter of type string, so you need to cast the value to a string first:

@Styles.Render(@Session["cssTheme"] as String)

然后，如果该会话变量根本未设置，或者已设置为无法转换为字符串的字符串值以外的其他值，则您可能会收到空值.因此，为了弥补这一点，您应该为空值提供一些后备:

Then, there's the problem that you could potentially receive a null value if either that session variable is not set at all, or has been set to something other than a string value that can't be converted to a string. So, to compensate for that, you should provide some fallback for nulls:

@Styles.Render(@Session["cssTheme"] as String ?? "~/Content/css")

现在，它要么使用会话变量中的任何内容，要么使用~/Content/css"作为最后的手段.但请记住，这仍然很脆弱.如果 Session["cssTheme"] 设置为字符串，但不是格式正确的包引用，您仍然会收到错误，并且会出现运行时错误，这很丑陋.理想情况下，您应该有某种值清理例程，在将其传递给 Styles.Render 之前先运行 Session["cssTheme"].

Now, it will either use whatever is in the session variable, or "~/Content/css" as a last resort. Bear in mind though, that this is still pretty brittle. If Session["cssTheme"] is set to a string, but not a properly formatted bundle reference, you'll still get an error, and a runtime error at that, which is ugly. Ideally, you should have some sort of value sanitization routine that you run Session["cssTheme"] through first before passing it to Styles.Render.

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