ASP.NET Core 2.1 在函数外使用变量

Question

I have this TypeFilter

[TypeFilter(typeof(ValidateRolesFilter), Arguments = new object[] {
      configuration["key"], RoleGlobals.SystemAdministrator
})]
public IActionResult About()
{
    return View();
}

In the class constructor above, I have declared configuration like this

public HomeController(IApplicationUserClient getUserClient, IConfiguration configuration)
{
    this.getUserClient = getUserClient;
    this.configuration = configuration;
}

However, when I try to declare configuration["Item"], in my typefilter, it won't let me. I can only do it inside functions.

What can I do to make it so that I can use my configuration variable outside the function? I tried making it a constant but it didn't work because it reads from appsettings.json.

Answer 1

You don't.

[TypeFilter(typeof(ValidateRolesFilter), Arguments = new object[] {
  configuration["key"], RoleGlobals.SystemAdministrator})]

The line above it what is called an Attributes (C#) . Attributes are compile time directives that can read at runtime.

The variable configuration["key"] is loaded at run-time. Therefore the compiler will fail.

Here is another design. Instantiate the ValidateRolesFilter in your constructor.

public HomeController(IApplicationUserClient getUserClient, IConfiguration configuration)
{
    this.getUserClient = getUserClient;
    this.configuration = configuration;

    // This is just a guess; I have no idea what this object is
    this.canAccessAbout = new ValidateRolesFilter(configuration["key"], RoleGlobals.SystemAdministrator);
}

Then in your About method:

public IActionResult About()
{
    // again, this is just a guess 
    if (this.canAccessAbout.Validate())
    {
        return View();
    }
    else
    {
        // redirect them or display error page
    }
}