如何创建全局变量,ASP.NET,全局asax

<appSettings>
  <add key="GlobalVariable" value="GlobalValue"/>
</appSettings>

string globalVariable = ConfigurationManager.AppSettings["GlobalVariable"];

protected void Application_Start(object sender, EventArgs e)
{
    Application["GlobalVariable"] = "GlobalValue";
}

string globalVariable = (string)HttpContext.Current.Application["GlobalVariable"];

protected void Application_Start(object sender, EventArgs e)
{
    HttpContext.Current.Cache["GlobalVariable"] = "GlobalValue";
}

string globalVariable = (string)HttpContext.Current.Cache["GlobalVariable"];

public static class GlobalVariables
{
    public static string GlobalVariable = "GlobalValue";
}

string globalVariable = GlobalVariables.GlobalVariable;