ASP.NET Mobile Handset Detection, Redirection & Development Made Easy
Introduction
This article explains two approaches to determine if an HTTP request is coming from a mobile phone and then redirecting the request to a page optimized for a mobile browser.
Overview
Today almost all web sites are designed to operate on a desktop or laptop computer. Anyone operating marketing, ecommerce, information or entertainment web sites now needs to consider the mobile phone when designing content and services. Mobile web sites development is increasing day by day and so is the number of different mobile devices trying to access the web sites. Major problems for web developers for mobile website development are following:
i)Detect mobile device and redirect user to mobile website
E.g. practical client requirement:Apple users should be redirected to an Apple theme url , RIM (BlackBerry) users should be redirected to a Blackberry theme url and all other mobile devices should be redirected to a standard mobile theme url.
ii) Mobile device database to fetch mobile capabilities in order to deliver the best possible experience to mobile users
E.g. does this phone support java or flash, or what kind of entry method is available, such as a qwerty keyboard or a touch screen?Approach 1: Use ASP.NET to Detect The User-Agent
It is the standard method used by most of the web developers today. Device database used is MDBF [This project is no longer supported and is removed on October 29, 2010]. So the big question again, which device database to use, which is up to date, and has a wide range of mobile device information? Adding server-side browser detection and redirection to your website using the ASP.net platform is quite easy. This code should be inserted into the Page_Load event of the web form code behind file (e.g. default.aspx.cs). To enable this site-wide, just add it to the Page_Load event of the Master Page file.
Approach 1
string userAgent = Request.UserAgent.ToString().ToLower();
if (userAgent != null)
{
if (Request.Browser.IsMobileDevice == true)
{
if (userAgent.Contains("iphone"))
Response.Redirect("~/Apple/Default.aspx");
else if (userAgent.Contains("nokia"))
Response.Redirect("~/Nokia/Default.aspx");
else
Response.Redirect("~/Mobile/Default.aspx");
}
}
In the code above you can add as many user agents as you wish. The else statement is not necessary in this case, because we want the page to load normally when the request is coming from standard browsers. Limitations of above code are:
- It will not catch all mobile browsers as there are a lot of them.
- You need to keep updating user agents when new devices are introduced.
- Not easy to parse user agents to get detailed information about the mobile device such as the manufacturer, model, screen height & width, and image formats supported. This type of information is necessary to customize page layout to the specific mobile device.
Approach 2: Use 51degrees.codeplex.com .NET Mobile API To Detect The User-Agent
51Degrees.mobi provides a free open source .NET mobile API allowing Visual Basic and C# developers to benefit from the extensive mobile device information available in WURFL also used by the BBC, Bank of America, MySpace and Admob among others. WURFL device database is widely-accepted as the most advanced and up-to-date mobile device database available.The following steps demonstrate how to detect a mobile device, obtain accurate device details and easily redirect to a mobile landing page overcoming the limitations of Approach 1.
With this approach there is no need to update your existing web pages of desktop website. You just need to update web.config and copy couple of files to your website as explained below.
Step 1: Use existing or create new standard ASP.NET web site using Visual Studio
Step 2: 51Degrees.mobi resource download
Following files need to be added to the web site created in Step1.
- App_Data/wurfl.xml.gz
- App_Data/web_browsers_patch.xml
- bin/ FiftyOne.Foundation.dll
These files can be extracted from the Enhance Download Enhancement_Library.zip - 148.37 KB
Once downloaded your website should have following folders. 
Step 3: Web.config Settings
Following sections need to be added to the web.config file of your web site to make use of the API.i) Configuration section:
The following settings are needed at the top of the web.config file. They tell .NET about subsequent configurations in the web.config and how to handle them. In this instance we're telling .NET to use the Mobile assembly.Web.config Setting 1:
<configSections>
<sectionGroup name="fiftyOne">
<section name="log" type="FiftyOne.Foundation.Mobile.Configuration.LogSection, FiftyOne.Foundation" requirePermission="false" allowDefinition="Everywhere" restartOnExternalChanges="false" allowExeDefinition="MachineToApplication"/>
<section name="redirect" type="FiftyOne.Foundation.Mobile.Configuration.RedirectSection, FiftyOne.Foundation" requirePermission="false" allowDefinition="Everywhere" restartOnExternalChanges="false" allowExeDefinition="MachineToApplication"/>
<section name="wurfl" type="FiftyOne.Foundation.Mobile.Detection.Wurfl.Configuration.WurflSection, FiftyOne.Foundation" requirePermission="false" allowDefinition="Everywhere" restartOnExternalChanges="false" allowExeDefinition="MachineToApplication"/>
</sectionGroup>
</configSections>
ii) Add new <fiftyOne> section:
Add the following mobile element after the configSections element. These lines control how the Mobile API responds to mobile devices and where to locate the database of mobile devices.
Web.config Setting 2:
<fiftyOne>
<!--<redirect> element controls how requests from mobile devices are handled.
mobileHomePageUrl A url to direct mobile devices to instead of the normal web sites
landing page. (Optional)
firstRequestOnly If set to true only the first request received by the web site is
redirected to the mobileUrl when the site is accessed from a mobile
device. (Optional – defaults to true)
timeout The number of minutes of inactivity that should occur before the
requesting device should be treated as making a new request to the
web site for the purposes of redirection. If the session is available
the session timeout will be used and override this value. (Optional
-defaults to 20 minutes)
devicesFile A file used to store the details of devices that have previously
accessed the web site to determine if they're making a subsequent
request. Needed to ensure multiple worker processes have a consistent
view of previous activity. (Optional – random behaviour will be
experienced if not specified on web sites with more than one worker
processes)
mobilePagesRegex A regular expression that when applied to the current request Path
(context.Request.AppRelativeCurrentExecutionFilePath) or the requesting
Urlwill return true if it should be considered a mobile page. Use
this attribute to tell redirection about mobile pages derived from base
classes such as System.Web.UI.Page. Redirection needs to be aware of
mobile pages so that requests to these pages can be ignored. Any page
that derives from System.Web.UI.MobileControls.MobilePage will
automatically be treated as a mobile page irrespective of this
attribute. (Optional)
originalUrlAsQueryString
If set to true the redirected URL will have the original requesting Url
encoded and included as the origUrl query string parameter in the
redirected Url. This will enable the mobile home page to determine the
original requested resource providing the option to display a mobile
friendly version. (Optional – defaults to false)
locations/location Provides details of different locations requests can be directed to based
on the values of defined properties associated with the device or request.
(Optional)
url the URL of the redirect location to use if all the properties in the
collection match. (Mandatory)
matchExpression can be used to provide a regular expression which will take the requesting
URL as input match segments to be used in place of numeric parameters contained
within {} in the url attribute. (Optional)
The location element contains a collection of criteria that all need to match
for the location to be used. Two attributes must be specified with each entry.
property the property of HttpRequest, HttpRequest.Browser or WURFL capability to
use when evaluating the matchExpression attribute. (Mandatory)
matchExpression a regular expression used to evaluate the value of the property. (Mandatory)
-->
<redirect firstRequestOnly="true"
mobileHomePageUrl="~/Mobile/Default.aspx"
timeout="20"
devicesFile="~/App_Data/Devices.dat"
mobilePagesRegex="/(Mobile|Tablet|Apple)/">
<locations>
<!-- Don't redirect requests that have the noredirect query string parameter. -->
<location url="">
<add property="Url" matchExpression="[&|\?]noredirect"/>
</location>
<!—- Send tablets to their own home page. -->
<location url="~/Tablet/Default.aspx">
<add property="is_tablet" matchExpression="true"/>
</location>
<!—- Send iPhone to their own home page. -->
<location url="~/Apple/Default.aspx">
<add property="MobileDeviceManufacturer" matchExpression="Apple"/>
</location>
</locations>
</redirect>
<!--<log> element controls where and how much information should be recorded in the log.
logFile The location of the log file. (Mandatory)
logLevel Values include Debug|Info|Warn|Fatal and control the level of information
logged. Defaults to Fatal if not specified. (Optional)-->
<log logFile="~/App_Data/Log.txt" logLevel="Info"/>
<!--<wurfl> element controls device data and new device handling.
wurflFilePath is the path of the main wurfl file (mandatory).
wurflPatches defines where any additional patch files can be located (optional).
newDevicesURL provides a URL where new devices found on your server can be recorded
(optional).
newDeviceDetail can be "minimum" or "maximum" and controls the HTTP header
information sent to location defined in newDevicesUrl (optional).
useActualDeviceRoot When set to true only Wurfl devices marked with the attribute "actual_device_root"
are used to provide capabilities. Child devices will continue to be used to
for device matching but their capabilities will not be used. This is an advanced
feature for those familar with WURFL. (optional)
capabilitiesWhiteList Using the capabilityName attribute of the add elements lists the Wurfl capabilities
required by the mobile web application. Providing this list prevents the entire list
of capabilities from being loaded slightly improving performance.-->
<wurfl wurflFilePath="~/App_Data/wurfl.xml.gz" newDeviceDetail="maximum"
newDevicesURL="http://devices.51degrees.mobi/new.ashx" useActualDeviceRoot="false">
<capabilitiesWhiteList>
<add capabilityName="pointing_method"/>
</capabilitiesWhiteList>
<wurflPatches>
<add name="browser_definitions"
filePath="~/App_Data/web_browsers_patch.xml" enabled="true"/>
</wurflPatches>
</wurfl>
</fiftyOne>
Note: <locations> match and the requesting device is a mobile device then the mobileHomePageUrl will be used.
iii) Detector Module in web.config:
Add the following element to the httpModules element. These allow the Mobile API to intercept new page requests and redirect them if the requesting device is a mobile.Web.config Setting 3:
<!-- IIS 6.0 & Visual Studio - Registers a module that is used to detect any new requests to the web site.
Without this module mobile detection and redirection won't work.-->
<httpModules>
<add name="Detector" type="FiftyOne.Foundation.Mobile.Detection.DetectorModule, FiftyOne.Foundation"/>
</httpModules>
<!-- IIS 7.X - Registers a module that is used to detect any new requests to the web site.
Without this module mobile detection and redirection won't work.-->
<system.webServer>
<modules>
<remove name="Detector"/>
<add name="Detector" type="FiftyOne.Foundation.Mobile.Detection.DetectorModule, FiftyOne.Foundation"/>
</modules>
</system.webServer>
Web.config Setting 4:
<!-- To avoid errors due to Code Access Security (CAS) the web.config defaults to set trust level to full.-->
<trust level="Full">
iii) Detector Module in global.asax
The latest version, 0.1.11.8, provides another method to intercept using .NET 4 and global.asax, allowing for a slight boost in performance and a more elegant web.config. To do this the following code needs to be placed in global.asax:Global.asax Setting
#if VER4
using System;
using System.Web.Configuration;
#endif
namespace Detector
{
public class Global : System.Web.HttpApplication
{
#if VER4
protected void Application_Start(object sender, EventArgs e)
{
Enable the mobile detection provider.
HttpCapabilitiesBase.BrowserCapabilitiesProvider =
new FiftyOne.Foundation.Mobile.Detection.MobileCapabilitiesProvider();
}
protected void Application_AcquireRequestState(object sender, EventArgs e)
{
Process redirection logic.
FiftyOne.Foundation.Mobile.Redirection.RedirectModule.
OnPostAcquireRequestState(sender, e);
}
#endif
}
}
To allow this to work properly the modules section needs to be removed and the foundation.dll recompiled with the VER4 compiler signal. See below to see where to obtain the source code.
Step 4: Download Mobile Emulators To Test Web site
Please click here to get details for downloading Mobile Emulators to test website.Download Source Code:
Download Detection_Sample_Source.zip - 1.07 MB for the sample application explained in Approach2.
Result
When the website is accessed from mobile device, user will be redirected to appropriate mobile view. Unlike Approach 1 you do not have to write any code for redirection, it is taken care by the 51degrees.mobi .NET Mobile API. Apart from this .NET Mobile API also gives information of device capabilities which can be used for customization. It has simple access to the entire WURFL database that can be exposed in code, useful if you need to more advanced redirection that can utilize session variables or time of day or anything else that you need.
Accessing mobile capabilities:
string capability = Request.Browser["is_tablet"];
The entire list of WURFL capabilities can be found here.
Conclusion
If you’re developing mobile websites and struggling with the variety of mobile devices use Approach2 as explained above. It will reduce development time, uses device data you can trust and leaves you free to focus on delivering an amazing mobile experience.Resource
i) Click here for more details on .NETMobile API.ii) Click here for detailed information on web.config settings for .NETMobile API usage.
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