CFBridgingRetain与CFBridgingRelease的详细说明

在CoreFoundation框架和Foundation框架中有大量的可互换使用的数据类型。这意味着你可以使用相同的数据类型，作为CoreFoundation框架方法调用或Objective－C消息的参数或接收者。这种在CoreFoundation框架和Foundation框架之间交换使用数据类型的技术就叫 Toll-Free Bridging。

#if __has_feature(objc_arc)

// After using a CFBridgingRetain on an NSObject, thecaller must take responsibility for calling CFRelease at anappropriate time.

NS_INLINE CF_RETURNS_RETAINEDCFTypeRefCFBridgingRetain(id X) {

   return (__bridge_retainedCFTypeRef)X;

}

NS_INLINE idCFBridgingRelease(CFTypeRefCF_CONSUMED X) {

   return (__bridge_transferid)X;

}

#else

// This function is intended for use while converting toARC mode only.

NS_INLINE CF_RETURNS_RETAINED CFTypeRefCFBridgingRetain(id X) {

   return X ? CFRetain((CFTypeRef)X) :NULL;

}

// This function is intended for use while converting toARC mode only.

NS_INLINE idCFBridgingRelease(CFTypeRef CF_CONSUMED X) {

   return[(id)CFMakeCollectable(X)autorelease];

}

#endif

并不是多有的CF对象都支持 Toll-FreeBridging！

以下是支持该技术的类型表。

Core Foundation type	Foundation class	Availability
CFArrayRef	NSArray	OS X v10.0
CFAttributedStringRef	NSAttributedString	OS X v10.4
CFCalendarRef	NSCalendar	OS X v10.4
CFCharacterSetRef	NSCharacterSet	OS X v10.0
CFDataRef	NSData	OS X v10.0
CFDateRef	NSDate	OS X v10.0
CFDictionaryRef	NSDictionary	OS X v10.0
CFErrorRef	NSError	OS X v10.5
CFLocaleRef	NSLocale	OS X v10.4
CFMutableArrayRef	NSMutableArray	OS X v10.0
CFMutableAttributedStringRef	NSMutableAttributedString	OS X v10.4
CFMutableCharacterSetRef	NSMutableCharacterSet	OS X v10.0
CFMutableDataRef	NSMutableData	OS X v10.0
CFMutableDictionaryRef	NSMutableDictionary	OS X v10.0
CFMutableSetRef	NSMutableSet	OS X v10.0
CFMutableStringRef	NSMutableString	OS X v10.0
CFNumberRef	NSNumber	OS X v10.0
CFReadStreamRef	NSInputStream	OS X v10.0
CFRunLoopTimerRef	NSTimer	OS X v10.0
CFSetRef	NSSet	OS X v10.0
CFStringRef	NSString	OS X v10.0
CFTimeZoneRef	NSTimeZone	OS X v10.0
CFURLRef	NSURL	OS X v10.0
CFWriteStreamRef	NSOutputStream	OS X v10.0