Variable scope in aspx page

Why is that the scriptPath variable is out of scope in the bottom of the code?

Shouldn't it be in scope throughout this page? In MVC, if I mark this on top of the page like

@{
    string scriptPath = "assets/scripts/",
           gkoConfig = "GkoConfig.js";
}

it is available throughout the current View. What am I missing now that I'm back to WebForms for a while?

If I change the code position, It get's weirder as inside the <head> I no longer have access to teh variable, but I do have, inside the <body> now... :-/

回答1:

When you declare a variable in a Web Forms .aspx file, you’re actually declaring a local variable inside an auto-generated rendering method. ASP.NET generates separate rendering methods for all tags marked runat="server", so you actually get a separate method for your head element. Now, the variable you declare can only exist in one of these methods - hence the 'weird' behavior.

You can see how this works if you pre-compile your application using aspnet_compiler.exe. You will get compiled DLL files for each of your web forms pages; just open one of those up in Reflector to see the generated code. I wrote a minimal equivalent of your code with the variable declared outside the head tag, and here’s the top-level render method that I got:

private void __Render__control1(HtmlTextWriter __w, Control parameterContainer)
{
    string str = "scripts/";
    __w.Write("\r\n<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\">\r\n\r\n<html xmlns=\"http://www.w3.org/1999/xhtml\">\r\n");
    parameterContainer.Controls[0].RenderControl(__w);
    __w.Write("\r\n<body>\r\n    ");
    parameterContainer.Controls[1].RenderControl(__w);
    __w.Write("\r\n    <script type=\"text/javascript\" src=\"");
    __w.Write(str);
    __w.Write("jquery-1.4.1.min.js\"></script>\r\n</body>\r\n</html>\r\n");
}

You see that the variable that I declared (here named str) is scoped to this method, and it's calling other methods to render the head (and a form element marked runat="server".)

A quick and dirty solution might be to simply remove the runat="server" from your head tag; however, I’d recommend that you declare a protected variable in your code-behind class for this. Adding a line like this to your code-behind file would work:

protected string scriptPath, gkoConfig;

You can then use these variables anywhere in your Web Forms code.

回答2:

You could also declare your constants like this:

<script runat="server">
    private const string scriptPath = "assets/scripts/";
    private const string gkoConfig = "GkoConfig.js";
</script>

回答3:

I suspect the head of the ASPX page gets processed separately from the body.

This problem is easily solved - all you need to do is use a class field in the code-behind with the access level set to protected.