Foundation是OC的东西，CoreFoundation是C语言的东西
eg：
NSString\NSArray\NSDictionary 属于Foundation
CFStringRef\CFArrayRef\CFDictionaryRef: 属于CoreFoundation
转换时，使用__bridge做桥接。
Foundation----->CoreFoundation NSString * text = @"23"; CFStringRef str = (__bridge CFStringRef)text; CoreFoundation -----> Foundation NSString * str = (__bridge NSString *)KCFStringRef;