Objective-C对象与Core Foundation对象

Core Foundation 对象主要使用在用C语言编写的Core Foundation 框架中,并引用计数的对象.与Objective-C对象差别非常少.不管哪种框架生成的对象,一旦生成,便可在两种框架中使用.这样的转换不须要额外的CPU资源,因而也被称为”免费桥”.

/****************************(1)***********************/

/*

CFTypeRef CFBridgingRetain(id X){

return (__bridge_retained CFTypeRef)X;

}

id CFBridgingRelease(CFTypeRef X){

return (__bridge_transfer id)X;

}

*/

CFMutableArrayRef cfObject =
NULL;

{

id obj = [[NSMutableArray
alloc] init];

cfObject =
CFBridgingRetain(obj);

//也可使用 cfObject = (__bridge_retained CFMutableArrayRef)obj;

/*

ARC机制在 Core Foundation框架是否有效?

输出打印例如以下:

retain count = 2

retain count = 1

由此可知ARC机制在Core Foundation下并不起作用

*/

CFShow(cfObject);

printf("retain count = %ld\n",CFGetRetainCount(cfObject));

}

printf("retain count = %ld\n",CFGetRetainCount(cfObject));

CFRelease(cfObject);

/****************************(2)***********************/

//使用__bridge转换来替代CFBridgingRetain或__bridge_retained转换

/*

cfObject = (__bridge CFMutableArrayRef)obj;

但使用__bridge并不改变对象的持有情况.

*/