如何在ARC下使用CFMutableDictionaryRef

Question

如何在ARC下使用CFMutableDictionaryRef

objective-cautomatic-ref-countingcore-foundation

4

这是使用CFMutableDictionaryRef和ARC的正确方式吗？

CFMutableDictionaryRef myDict = CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
NSString *key = @"someKey";
NSNumber *value = [NSNumber numberWithInt: 1];
//ARC doesn't handle retains with CF objects so I have to specify CFBridgingRetain when setting the value
CFDictionarySetValue(myDict, (__bridge void *)key, CFBridgingRetain(value));
id dictValue = (id)CFDictionaryGetValue(myDict, (__bridge void *)key);
//the value is removed but not released in any way so I have to call CFBridgingRelease next
CFDictionaryRemoveValue(myDict, (__bridge void *)key);
CFBridgingRelease(dictValue);//no leak

- joels

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- rob mayoff · Accepted Answer

不要在这里使用 CFBridgingRetain 和 CFBridgingRelease。此外，在强制转换 CFDictionaryGetValue 的结果时，需要使用 __bridge。

CFMutableDictionaryRef myDict = CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
NSString *key = @"someKey";
NSNumber *value = [NSNumber numberWithInt: 1];
CFDictionarySetValue(myDict, (__bridge void *)key, (__bridge void *)value);

id dictValue = (__bridge id)CFDictionaryGetValue(myDict, (__bridge void *)key);
CFDictionaryRemoveValue(myDict, (__bridge void *)key);

由于字典本身会保留值，所以不需要使用 CFBridgingRetain。如果您没有调用 CFBridgingRetain，则无需后续释放。

总之，如果您只是需要一个 NSMutableDictionary，那么这些都会简单得多，只需创建它即可，如果您需要一个 CFMutableDictionary，则可以将其强制转换：

NSMutableDictionary *myDict = [NSMutableDictionary dictionary];
NSString *key = @"someKey";
NSNumber *value = [NSNumber numberWithInt: 1];
[myDict setObject:value forKey:key];

CFMutableDictionaryRef myCFDict = CFBridgingRetain(myDict);
// use myCFDict here
CFRelease(myCFDict);

请注意，CFBridgingRetain 可以通过 CFRelease 进行平衡；除非需要它返回的 id，否则不必使用 CFBridgingRelease。同样地，您可以使用 CFBridgingRelease 平衡 CFRetain。