Objective-C指针类型'NSString *'转换为C指针类型'CFStringRef'（aka'const struct __CFString *'）需要一个桥接 [英] cast of Objective-C pointer type 'NSString *' to C pointer type 'CFStringRef' (aka 'const struct __CFString *') requires a bridged cast

问题描述

将Objective-C程序转换为Objective-C ARC时，会出现以下错误：

When converting an Objective-C program to a Objective-C ARC, I get the error:

"cast of Objective-C pointer type 'NSString *' to C pointer type 'CFStringRef' (aka 'const struct __CFString *') requires a bridged cast "

代码如下：

- (NSString *)_encodeString:(NSString *)string
{
    NSString *result = (NSString *)CFURLCreateStringByAddingPercentEscapes(NULL, 
                                   (CFStringRef)string, // this is line in error
                                   NULL, 
                                   (CFStringRef)@";/?:@&=$+{}<>,",
                                   kCFStringEncodingUTF8);
    return [result autorelease];
}

什么是桥梁施法？

推荐答案

查看 ARC文档 LLVM网站。您必须使用 __ bridge 或其他关键字之一。

Have a look at the ARC documentation on the LLVM website. You'll have to use __bridge or one of the other keywords.

这是因为Core Foundation对象* Refs）不受ARC控制，只有Obj-C对象。所以当你在它们之间转换，你必须告诉ARC关于对象的所有权，以便它可以正确清理。最简单的情况是 __ bridge cast，ARC不会做任何额外的工作（它假设你自己处理对象的内存）。

This is because Core Foundation objects (CF*Refs) are not controlled by ARC, only Obj-C objects are. So when you convert between them, you have to tell ARC about the object's ownership so it can properly clean them up. The simplest case is a __bridge cast, for which ARC will not do any extra work (it assumes you handle the object's memory yourself).

这篇关于Objective-C指针类型'NSString *'转换为C指针类型'CFStringRef'（aka'const struct __CFString *'）需要一个桥接的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！