Question

我正在使用一个供应商API，它返回一个CFDictionaryRef，它可以包含各种CF对象类型，调用者需要CFRelease。我想将它转换为NSDictionary以便更容易地使用它，并且希望确保我理解我正在按照强制转换处理元素。

在我看来，像免费的桥接类型（例如CFString，CFNumber）只是由NSDictionary处理，我可以像我一样，如果他们一直是Obj-C类型那样得到NS类型（我是猜测封面下有一座桥梁。）

对于非免费桥接类型（例如CFHost），看起来我可以将-valueForKey：的结果转换为CF类型并从那里开始，但是如果我需要释放那个，我不是肯定的价值与否。

以下是一些说明问题的示例代码。这是处理事情的正确方法吗？

// Caller is responsible for releasing returned value
//
+ (CFDictionaryRef)someCFCreateFunctionFromVendor
{
    CFMutableDictionaryRef cfdict = CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
    CFDictionarySetValue(cfdict, CFSTR("string1"), CFSTR("value"));
    int i = 42;
    CFDictionarySetValue(cfdict, CFSTR("int1"), CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &i));

    CFHostRef host = CFHostCreateWithName(kCFAllocatorDefault, CFSTR("myhost"));
    CFDictionarySetValue(cfdict, CFSTR("host1"), host);
    return cfdict;
}

+ (void)myMethod
{
    NSDictionary *dict = CFBridgingRelease([self someCFCreateFunctionFromVendor]);
    for (NSString *key in [dict allKeys]) {
        id value = [dict valueForKey:key];
        NSLog(@"%@ class: %@", key, [value class]);

        if ([value isKindOfClass:[NSString class]]) {
            NSString *str = (NSString *)value;
            NSLog(@"%@ is an NSString with value %@", key, str);
        } else if ([value isKindOfClass:[NSNumber class]]) {
            NSNumber *num = (NSNumber *)value;
            NSLog(@"%@ is an NSNumber with value %@", key, num);
        } else if ([value isKindOfClass:[NSHost class]]) {
            NSLog(@"%@ is an NSHost", key); // never hit because no toll-free bridge to NSHost
        } else {
            NSLog(@"%@ is an unexpected class", key);
        }

        // Sample handling of non-toll-free bridged type
        if ([key isEqualToString:@"host1"]) {
            CFHostRef host = (__bridge CFHostRef)value;
            NSArray *names = (__bridge NSArray *)(CFHostGetNames(host, false));
            NSLog(@"host1 names: %@", names);
            // I don't think I need to CFRelease(host) because ARC is still handling value
        }
    }
}

...输出

string1 class: __NSCFConstantString
string1 is an NSString with value strvalue 
int1 class: __NSCFNumber
int1 is an NSNumber with value 42
host1 class: __NSCFType
host1 is an unexpected class
host1 names: ( myhost )

Answer 1

具有讽刺意味的是，您的代码中唯一的错误是在Core Foundation中，非ARC内容。您的+someCFCreateFunctionFromVendor方法调用CFNumberCreate()和CFHostCreateWithName()，两者都是创建函数，但在将对象添加到字典后不会CFRelease()。这应该。否则，这是泄漏。顺便说一下，静态分析仪会抓住它。（对于CFNumber，这意味着您必须将创建拆分为单独的行，以便在将对象添加到字典后引用该对象。）

您不得在+myMethod中释放主机对象，因为该代码不会获得它的所有权。它与ARC无关。你不会在MRR（手动保留/释放）代码中发布它。

桥梁为集合元素强制转换

1 个答案: