静态变量ASP.NET

Question

in asp.net web application if I want to store variable in a static object is that right? I don't want that this object will share its value with another request.

public static object Objects
{
    get
    {
        if (HttpContext.Current.Items["Objects"] != null)
            return (object)HttpContext.Current.Items["Objects"];
        else
        {
            HttpContext.Current.Items["Objects"] = new object();
            return new object();
        }
    }

    set { HttpContext.Current.Items["Objects"] = value; }
}

THX

Answer 1

Static fields are shared across the whole AppDomain. This means that ALL requests in a ASP.NET web application will use the same value and you will have to make sure that variable is thread-safe. If this is not what you want, consider the following:

• Storing the value in the user session: HttpContext.Current.Session
• Storing the value in the request: HttpContext.Current.Items . This way the value is cached throughout the current request, but not shared across requests.
• Don't store the value at all.

In your case however, you are using a static property. This static property maps in your case to the HttpContext.Current.Items , which means that each request automatically gets its own variable and variables are not shared.

In other words, your code is thread-safe.

Answer 2

I don't want that this object will share its value with another request.

You should not make it static then.

Answer 3

If you want to use a static variable without sharing it across all requests you could store a session variable in a static property. Use HttpContext.Session to access it.

public static object Objects  
{
    get
    {
        if (HttpContext.Current.Session["Objects"] != null)
            return (object)HttpContext.Current.Session["Objects"];
        else
        {
            var obj = new object();
            HttpContext.Current.Session["Objects"] = obj;
            return obj;
        }
    }

    set { HttpContext.Current.Session["Objects"] = value; }
}

However, you should not return object but the correct type, that will increase readability, prevents exceptions and avoids always casting it where you use it.

Answer 4

There are 4 main server Dictionary objects that store values between requests. Application - shares values between all requests and users. Cache - shares values between all requests and users but can be invalidated without restarting application. Session - shares values between requests within the same session, all pages share the same session object, and is user specific. ViewState - shares values between request but is page specific and user specific.

Answer 5

if you want the benefit of static across a single request. That is, have a single request have access to the same value. Use a session variable instead.

Session['variable'] = value

this will store the value in the current session, this way you will have a different value per request.