objective-c - 如何在 ARC 中使用 CFMutableDictionaryRef

Question

这是你应该如何将 CFMutableDictionaryRef 与 ARC 一起使用？

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

Answer 1

不要在这里使用CFBridgingRetain 和CFBridgingRelease。此外，在转换 CFDictionaryGetValue 的结果时，您需要使用 __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);

不需要CFBridgingRetain，因为字典无论如何都会保留值。如果您不调用 CFBridgingRetain，则无需在稍后发布时平衡它。

无论如何，如果您只是创建一个 NSMutableDictionary，然后，如果您需要一个 CFMutableDictionary，则强制转换它:

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；您不必使用 CFBridgingRelease 除非您需要它返回的 id。同样，您可以平衡 CFRetain 与 CFBridgingRelease。