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Resources » Articles » ASP.NET/Web Applications »
Guide to State Management Techniques in ASP.NET
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HTTP Protocol and the Need for State Management Techniques
Hyper Text Transfer Protocol (HTTP) is a communication protocol which is implemented in the "World Wide Web(WWW)". It is a request/response style protocol. Clients (browsers, spider, etc) will request to a server (web server) and the server responds to these requests. HTTP uses TCP protocol for communication. It connects to a specific port (default is 80) to the server and communicates via that port. Once the response is received completely, client programs will be disconnected from the server. For each request, client programs have to acquire a connection with servers and do all the request cycles again.
ASP.NET files are just text files which will be placed in the server and served upon the request. When a request comes for a page, the server will locate the requested file and ask the ASP.NET engine to serve the request. The ASP.NET engine will process the server tags and generate HTML for it and return back to the client. HTTP is a stateless protocol and the server will abandon the connection once the request is served.
Since HTTP is stateless, managing state in web applications is challenging. State management techniques are used to maintain user state throughout the application. Managing state in a stand-alone application is trivial as they don't have a request/response nature. Information you want to maintain over the lifetime of a web applications depends on your context. It can be from simple numbers to very complex objects.
Understanding the state management techniques play a major role in creating efficient web applications. ASP.NET is very rich in state management techniques. The following are the commonly used state management techniques.
QueryString
Cookies
Cache
ViewState
Session state
Application state
Static variables
Profiles
Cache and ViewState are already explained in the previous sections and this article will not cover it.
QueryString
This is the most simple and efficient way of maintaining information across requests. The information you want to maintain will be sent along with the URL. A typical URL with a query string looks like
www.somewebsite.com/search.aspx?query=foo
The URL part which comes after the ? symbol is called a QueryString. QueryString has two parts, a key and a value. In the above example, query is the key and foo is its value. You can send multiple values through querystring, separated by the & symbol. The following code shows sending multiple values to the foo.aspx page.
Response.Redirect("foo.aspx?id=1&name=foo");
The foo.aspx page will get the values like in the following table.
Key Value
id 1
name foo
The following code shows reading the QueryString values in foo.aspx
string id = Request.QueryString["id"];
string name = Request.QueryString["name"];
Request.QueryString has two overloaded indexers. One accepts the key name and another a zero-based index. The latter is useful when you don't know the query string names. If you try to get a value which is not in the QueryString collection, you will get a NULL reference.
QueryString Encoding
The URL RFC [^] states that, a URL can have only ASCII characters. So all the other characters should be encoded when you pass through the URL. The .NET Framework provides the HttpServerUtility.UrlEncode class to encode the URL.
The following code shows how name and id is passed to foo.aspx page as encoded.
string id = "1";
string name = "foo#";
string url = string.Format("foo.aspx?{0}&{1}", Server.UrlEncode(id), Server.UrlEncode(name));
Response.Redirect(url);
// decoding can be done using it's counter part HttpServerUtility.UrlDecode()
string id = Server.UrlDecode(Request.QueryString["id"]);
string name = Server.UrlDecode(Request.QueryString["name"]);
Note: HttpServerUtility is available to your code in all webforms through the Page.Server property. Also you only need to encode those values which have non-ASCII characters, not all the values.
Reading QueryString Safely
I have seen many people use code as shown below to read values from a QueryString collection
// Bad practice - Don't use!
Request.QueryString["id"].ToString();
This is hilarious. Request.QueryString[key] returns a string and has no need to convert it again to string. Another problem with the above code is, Request.QueryString[key] will return NULL if the specified key not found in the collection. In such cases, calling Request.QueryString[key].ToString() will lead to a NullReferenceException. The following code shows reading a QueryString value safely.
string queryStringValue = Request.QueryString["key"];
if (string.IsNullOrEmpty(queryStringValue)) {
// querystring not supplied. Do necessary action
}
else
// Querystring supplied. continue execution
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