Evaluating Capabilities Programmatically 

For ASP.NET mobile controls, the functionality provided through the <deviceFilters> section of the Web.config file can be accessed programmatically using the HasCapability method of the MobileCapabilities class. By calling this method, you can evaluate comparison methods.

The HasCapability method is useful for programmatically determining whether the current device satisfies a device filter declared in the Web.config file. The MobileCapabilities instance caches the evaluation of the HasCapability method so that subsequent requests for the same capability name and optional argument do not need to be reevaluated. The HasCapability method is useful when you want to write code that matches how the ASP.NET page framework selects among various choices in a <DeviceSpecific> element.

Note
The HasCapability method does not support <DeviceSpecific> element choices that call methods defined on the page.

The HasCapability method takes two arguments: capabilityName, which is the name of the device evaluation method, property, or item in the capability dictionary; and optionalArgument, which is any argument that the capabilityName argument requires. The HasCapability method performs its evaluation in the following order:

1. It checks whether capabilityName value is the name of a device filter specified in the Web.config file.

   Note
   The HasCapability method evaluates the <DeviceSpecific> and <Choice> construct by setting the optionalArgument argument to null.

2. If the test in step 1 returns true and the filter is a delegated evaluator (a filter that uses a custom method to evaluate the specified data), the HasCapability method invokes the delegate with the argument provided in the optionalArgument parameter and returns the result.

3. If the test in step 1 is true and the filter is a comparison evaluator (a filter that compares a capability name to a specified value), the HasCapability method calls itself with the capability name and argument provided in the evaluator (any original optionalArgument parameter is ignored) and returns the result.

4. If the MobileCapabilities object has a property named capabilityName, the HasCapability method casts this property to a string and returns true if the optionalArgument value is equal to this string. Boolean comparisons are not case-sensitive; other comparisons are case-sensitive. Therefore, "true" is equivalent to "True", but "left" is not equivalent to "Left".

5. If no capabilityName property exists, the HasCapability method looks in the capabilities dictionary associated with the MobileCapabilities object. If the capabilityName property exists, the HasCapability method compares it to the optionalArgument parameter and returns the result. Because the dictionary maintains strings, no casting is required.

6. If these tests fail, the HasCapability method throws an ArgumentOutOfRangeException exception.

Examples

The following examples show how you might call the HasCapability method, where GPSEnabled and ScreenBitDepth are defined filters, properties, or values in the Items collection.

((MobileCapabilities)Request.Browser).HasCapability("GPSEnabled", null);

Alternatively, you can call the method as follows:

((MobileCapabilities)Request.Browser).HasCapability("ScreenBitDepth", "8");

See Also

Reference

Device Capabilities Table
<filter> Element

Concepts

Device Evaluation Methods
Device Filtering Recommendations
Device-Specific Rendering