Objective-C Programming Summary (article 2) Type Determination

Objective-C provides a good type judgment and reflection mechanism. The foundation of OC isC LanguageAll objects are represented by pointers. The actual type information of a pointer may be blurred during transmission. You can use type queries to solve many programming problems. In addition, method calls in OC are message-based. It is also a common function to query whether a type contains a message response.

For example, an nsurlrequest object is obtained during HTTP network communication. When writing header information, you need to check whether it is mutablerequest:

If ([req ismemberofclass: [nsmutableurlrequest class])

Or

If ([req iskindofclass: [nsmutableurlrequest class])

The difference between the two statements is:

1. If the ismemberofclass type is identical, true is returned. If the instance is a subclass of the type, false is returned.

2. Determine whether iskindofclass contains sub-classes.

 

Obtain an nsurlresponse. to read the response header field, first determine whether it contains the allheaderfields method:

If ([Response responsestoselector: @ selector (allheaderfields)])

You can also write

If ([[response class] instancesrespondtoselect: @ selector (allheaderfields)]).

 

If you need to know whether the instance has implemented an interface, use:

If ([Request conformstoprotocol: nsprotocolfromstring (@ "nscopying")])