Toll-Free Bridging

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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 = [[NSLocale alloc] 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;

[myNSLocale autorelease];

NSString *nsIdentifier = [myNSLocale localeIdentifier];

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
13-1  Data 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)