Understand __Bridge

  I didn't understand the __bridge properly for a long time so that i took some hours to read documentation.

  from documentation,I know what's the duty of the core key__bridge.

  Ok.

  Duty: Convert Objective-c type into CoreFoundation type and reconvert.

  There are three methods to do this:

  Get from Documentation:

• __bridge transfers a pointer between Objective-C and Core Foundation with no transfer of ownership.(weak references)

• __bridge_retained or CFBridgingRetain casts an Objective-C pointer to a Core Foundation pointer and also transfers ownership to you.

  You are responsible for calling CFRelease or a related function to relinquish ownership of the object.(strong references, you have to call CFRelease to relinquish memory Because the ownership transfer to yourself)

• __bridge_transfer or CFBridgingRelease moves a non-Objective-C pointer to Objective-C and also transfers ownership to ARC.

  ARC is responsible for relinquishing ownership of the object.(Reconvert to objective-c and take the ownership to ARC)

  
  

  Example from documentation:

  NSLocale *gbNSLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_GB"];

  CFLocaleRef gbCFLocale = (__bridge CFLocaleRef)gbNSLocale;

  CFStringRef cfIdentifier = CFLocaleGetIdentifier(gbCFLocale);

  NSLog(@"cfIdentifier: %@", (__bridge NSString *)cfIdentifier);

  // Logs: "cfIdentifier: en_GB"

  CFLocaleRef myCFLocale = CFLocaleCopyCurrent();

  NSLocale *myNSLocale = (NSLocale *)CFBridgingRelease(myCFLocale);

  NSString *nsIdentifier = [myNSLocale localeIdentifier];

  CFShow((CFStringRef)[@"nsIdentifier: " stringByAppendingString:nsIdentifier]);

  // Logs identifier for current locale