我想了解从 ARC 中的 CFStringRef
获取 NSString
的正确方法?
反方向也一样,ARC中的CFStringRef
到NSString
?
在不造成内存泄漏的情况下,正确的方法是什么?
最佳答案
通常
NSString *yourFriendlyNSString = (__bridge NSString *)yourFriendlyCFString;
和
CFStringRef yourFriendlyCFString = (__bridge CFStringRef)yourFriendlyNSString;
现在,如果你想知道为什么会有 __bridge
关键字,你可以引用 Apple documentation .在那里你会发现:
__bridge
transfers a pointer between Objective-C and Core Foundation with no transfer of ownership.
__bridge_retained
orCFBridgingRetain
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.
__bridge_transfer
orCFBridgingRelease
moves a non-Objective-C pointer to Objective-C and also transfers ownership to ARC. ARC is responsible for relinquishing ownership of the object.
这意味着在上述情况下,您正在转换对象而不更改所有权。 这意味着在这两种情况下,您都将负责处理字符串的内存。
也有可能出于某种原因您想要转让所有权。
例如考虑以下代码段
- (void)sayHi {
CFStringRef str = CFStringCreateWithCString(NULL, "Hello World!", kCFStringEncodingMacRoman);
NSString * aNSString = (__bridge NSString *)str;
NSLog(@"%@", aNSString);
CFRelease(str); //you have to release the string because you created it with a 'Create' CF function
}
在这种情况下,您可能希望在转换时通过转移所有权来保存 CFRelease
。
- (void)sayHi {
CFStringRef str = CFStringCreateWithCString(NULL, "Hello World!", kCFStringEncodingMacRoman);
NSString * aNSString = (__bridge_transfer NSString *)str;
// or alternatively
NSString * aNSString = (NSString *)CFBridgingRelease(str);
NSLog(@"%@", aNSString);
}
str
的所有权已经转移,所以现在 ARC 将启动并为您释放内存。
另一方面,您可以使用 __bridge_retained
转换将 NSString *
转换为 CFString
,这样您就可以拥有该对象您必须使用 CFRelease
显式释放它。
你可以把它包起来
// Don't transfer ownership. You won't have to call `CFRelease`
CFStringRef str = (__bridge CFStringRef)string;
// Transfer ownership (i.e. get ARC out of the way). The object is now yours and you must call `CFRelease` when you're done with it
CFStringRef str = (__bridge_retained CFStringRef)string // you will have to call `CFRelease`
// Don't transfer ownership. ARC stays out of the way, and you must call `CFRelease` on `str` if appropriate (depending on how the `CFString` was created)
NSString *string = (__bridge NSString *)str;
// Transfer ownership to ARC. ARC kicks in and it's now in charge of releasing the string object. You won't have to explicitly call `CFRelease` on `str`
NSString *string = (__bridge_transfer NSString *)str;
关于objective-c - NSString 到 CFStringRef 和 CFStringRef 到 ARC 中的 NSString?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/17227348/
相关文章:
iphone - iOS SDK - 以编程方式生成 PDF 文件
iphone - Objective-C 将 NSDate 设置为当前 UTC
objective-c - 如何在 Swift 项目中使用 Objective-C CocoaPod
objective-c - Objective-c 中的 "instance variable"和
iphone - NSLocale currentLocale 总是返回 "en_US"而不是用户的
ios - 自定义 UITableViewCell 选择样式?