Toll-Free Bridging
There are a number of data types in the Core Foundation framework and the Foundation framework that can be used interchangeably. This capability, called toll-free
bridging, means that you can use the same data type as the parameter to a Core Foundation function call or as the receiver of an Objective-C message. For example, NSLocale (see NSLocale
Class Reference) is interchangeable with its Core Foundation counterpart, CFLocale (see CFLocale
Reference). Therefore, in a method where you see an NSLocale * parameter, you can pass a CFLocaleRef,
and in a function where you see a CFLocaleRef parameter, you can pass an NSLocale instance.
You cast one type to the other to suppress compiler warnings, as illustrated in the following example.
NSLocale *gbNSLocale = [ initWithLocaleIdentifier:@"en_GB"];
CFLocaleRef gbCFLocale = (CFLocaleRef) gbNSLocale;
CFStringRef cfIdentifier = CFLocaleGetIdentifier (gbCFLocale);
NSLog(@"cfIdentifier: %@", (NSString *)cfIdentifier);
// logs: "cfIdentifier: en_GB"
CFRelease((CFLocaleRef) gbNSLocale);
CFLocaleRef myCFLocale = CFLocaleCopyCurrent();
NSLocale * myNSLocale = (NSLocale *) myCFLocale;
;
NSString *nsIdentifier = ;
CFShow((CFStringRef) [@"nsIdentifier: " stringByAppendingString:nsIdentifier]);
// logs identifier for current locale
Note from the example that the memory management functions and methods are also interchangeable—you can use CFRelease with
a Cocoa object and release and autorelease with
a Core Foundation object.
Note: When using garbage collection, there are important differences to how memory management works for Cocoa objects and Core Foundation objects.
See “Using Core Foundation with Garbage Collection” for
details.
Toll-free bridging has been available since Mac OS X v10.0. Table
13-1 provides a list of the data types that are interchangeable between Core Foundation and Foundation. For each pair, the table also lists the version of Mac OS X in which toll-free bridging between them became available.
Table
13-1Data types that can be used interchangeably between Core Foundation and Foundation
Core Foundation type
Foundation class
Availability
CFArrayRef
NSArray
Mac OS X v10.0
CFAttributedStringRef
NSAttributedString
Mac OS X v10.4
CFCalendarRef
NSCalendar
Mac OS X v10.4
CFCharacterSetRef
NSCharacterSet
Mac OS X v10.0
CFDataRef
NSData
Mac OS X v10.0
CFDateRef
NSDate
Mac OS X v10.0
CFDictionaryRef
NSDictionary
Mac OS X v10.0
CFErrorRef
NSError
Mac OS X v10.5
CFLocaleRef
NSLocale
Mac OS X v10.4
CFMutableArrayRef
NSMutableArray
Mac OS X v10.0
CFMutableAttributedStringRef
NSMutableAttributedString
Mac OS X v10.4
CFMutableCharacterSetRef
NSMutableCharacterSet
Mac OS X v10.0
CFMutableDataRef
NSMutableData
Mac OS X v10.0
CFMutableDictionaryRef
NSMutableDictionary
Mac OS X v10.0
CFMutableSetRef
NSMutableSet
Mac OS X v10.0
CFMutableStringRef
NSMutableString
Mac OS X v10.0
CFNumberRef
NSNumber
Mac OS X v10.0
CFReadStreamRef
NSInputStream
Mac OS X v10.0
CFRunLoopTimerRef
NSTimer
Mac OS X v10.0
CFSetRef
NSSet
Mac OS X v10.0
CFStringRef
NSString
Mac OS X v10.0
CFTimeZoneRef
NSTimeZone
Mac OS X v10.0
CFURLRef
NSURL
Mac OS X v10.0
CFWriteStreamRef
NSOutputStream
Mac OS X v10.0
Note: Not all data types are toll-free bridged, even though their names might suggest that they are. For example, NSRunLoop is
not toll-free bridged to CFRunLoop, NSBundle is not toll-free bridged to CFBundle, and NSDateFormatter is
not toll-free bridged to CFDateFormatter.
(#add莫非桥接的均以Ref结尾)
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