Replacing the ASP.NET Browser Capabilities Functionality in asp.net 4.0
To replace the ASP.NET browser capabilities definition functionality completely, follow these steps:
1. Create a provider class that derives from HttpCapabilitiesProvider and that overrides the GetBrowserCapabilities method, as in the following example:
public class CustomProvider : HttpCapabilitiesProvider
{
public override HttpBrowserCapabilities
GetBrowserCapabilities(HttpRequest request)
{
HttpBrowserCapabilities browserCaps = new HttpBrowserCapabilities();
Hashtable values = new Hashtable(180, StringComparer.OrdinalIgnoreCase);
values[String.Empty] = request.UserAgent;
values["browser"] = "MyCustomBrowser";
browserCaps.Capabilities = values;
return browserCaps;
}
}
The code in this example creates a new HttpBrowserCapabilities object, specifying only the capability named browser and setting that capability to MyCustomBrowser.
2. Register the provider with the application.
In order to use a provider with an application, you must add the provider attribute to the browserCaps section in the Web.config or Machine.config files. (You can also define the provider attributes in a location element for specific directories in application, such as in a folder for a specific mobile device.) The following example shows how to set the provider attribute in a configuration file:
<system.web>
<browserCaps provider="ClassLibrary2.CustomProvider, ClassLibrary2,
Version=1.0.0.0, Culture=neutral" />
</system.web>
Another way to register the new browser capability definition is to use code, as shown in the following example:
void Application_Start(object sender, EventArgs e)
{
HttpCapabilitiesBase.BrowserCapabilitiesProvider =
new ClassLibrary2.CustomProvider();
// ...
}
This code must run in the Application_Start event of the Global.asax file. Any change to the BrowserCapabilitiesProvider class must occur before any code in the application executes, in order to make sure that the cache remains in a valid state for the resolved HttpCapabilitiesBase object.
Caching the HttpBrowserCapabilities Object
The preceding example has one problem, which is that the code would run each time the custom provider is invoked in order to get the HttpBrowserCapabilities object. This can happen multiple times during each request. In the example, the code for the provider does not do much. However, if the code in your custom provider performs significant work in order to get the HttpBrowserCapabilities object, this can result in huge overhead. To prevent this from happening, you can cache the HttpBrowserCapabilities object. Follow these steps:
1. Create a class that derives from HttpCapabilitiesProvider, like the one in the following example:
public class CustomProvider : HttpCapabilitiesProvider
{
public override HttpBrowserCapabilities
GetBrowserCapabilities(HttpRequest request)
{
string cacheKey = BuildCacheKey();
int cacheTime = GetCacheTime();
HttpBrowserCapabilities browserCaps =
HttpContext.Current.Cache[cacheKey] as
HttpBrowserCapabilities;
if (browserCaps == null)
{
HttpBrowserCapabilities browserCaps = new
HttpBrowserCapabilities();
Hashtable values = new Hashtable(180,
StringComparer.OrdinalIgnoreCase);
values[String.Empty] = request.UserAgent;
values["browser"] = "MyCustomBrowser";
browserCaps.Capabilities = values;
HttpContext.Current.Cache.Insert(cacheKey,
browserCaps, null, DateTime.MaxValue,
TimeSpan.FromSeconds(cacheTime));
}
return browserCaps;
}
}
In the example, the code generates a cache key by calling a custom BuildCacheKey method, and it gets the length of time to cache by calling a custom GetCacheTime method. The code then adds the resolved HttpBrowserCapabilities object to the cache. The object can be retrieved from the cache and reused on subsequent requests that need your custom provider.
2. Register the provider with the application as described in the preceding procedure.
Posted in: asp.net | Tags: asp.net asp.net 4.0 replace broser capabilities functionality httpcapabilitiesprovider httpbrowsercapabilities