objective-c - 创建自定义 CFType

Question

是否可以创建不派生的不透明类型CFTypeRef，可以使用CFRetain/保留/释放CFRelease？或者我如何从 a 派生新类型CFType？

Answer 1

我从来没有这样做过，但可以使用私有 API。很可能它将依赖于 OS X 的特定 dot 版本，因为 CF 运行时可能会因版本而异。无论如何，CF 是开源的，所以我看了一下CFRuntime的作用。我很高兴看到 Apple 举了一个例子：

// ========================= EXAMPLE =========================

// Example: EXRange -- a "range" object, which keeps the starting
//       location and length of the range. ("EX" as in "EXample").

// ---- API ----

typedef const struct __EXRange * EXRangeRef;

CFTypeID EXRangeGetTypeID(void);

EXRangeRef EXRangeCreate(CFAllocatorRef allocator, uint32_t location, uint32_t length);

uint32_t EXRangeGetLocation(EXRangeRef rangeref);
uint32_t EXRangeGetLength(EXRangeRef rangeref);


// ---- implementation ----

#include <CoreFoundation/CFBase.h>
#include <CoreFoundation/CFString.h>

struct __EXRange {
    CFRuntimeBase _base;
    uint32_t _location;
    uint32_t _length;
};

static Boolean __EXRangeEqual(CFTypeRef cf1, CFTypeRef cf2) {
    EXRangeRef rangeref1 = (EXRangeRef)cf1;
    EXRangeRef rangeref2 = (EXRangeRef)cf2;
    if (rangeref1->_location != rangeref2->_location) return false;
    if (rangeref1->_length != rangeref2->_length) return false;
    return true;
}

static CFHashCode __EXRangeHash(CFTypeRef cf) {
    EXRangeRef rangeref = (EXRangeRef)cf;
    return (CFHashCode)(rangeref->_location + rangeref->_length);
}

static CFStringRef __EXRangeCopyFormattingDesc(CFTypeRef cf, CFDictionaryRef formatOpts) {
    EXRangeRef rangeref = (EXRangeRef)cf;
    return CFStringCreateWithFormat(CFGetAllocator(rangeref), formatOpts,
        CFSTR("[%u, %u)"),
        rangeref->_location,
        rangeref->_location + rangeref->_length);
}

static CFStringRef __EXRangeCopyDebugDesc(CFTypeRef cf) {
    EXRangeRef rangeref = (EXRangeRef)cf;
    return CFStringCreateWithFormat(CFGetAllocator(rangeref), NULL,
        CFSTR("<EXRange %p [%p]>{loc = %u, len = %u}"),
        rangeref,
        CFGetAllocator(rangeref),
        rangeref->_location,
        rangeref->_length);
}

static void __EXRangeEXRangeFinalize(CFTypeRef cf) {
    EXRangeRef rangeref = (EXRangeRef)cf;
    // nothing to finalize
}

static CFTypeID _kEXRangeID = _kCFRuntimeNotATypeID;

static CFRuntimeClass _kEXRangeClass = {0};

/* Something external to this file is assumed to call this
 * before the EXRange class is used.
 */
void __EXRangeClassInitialize(void) {
    _kEXRangeClass.version = 0;
    _kEXRangeClass.className = "EXRange";
    _kEXRangeClass.init = NULL;
    _kEXRangeClass.copy = NULL;
    _kEXRangeClass.finalize = __EXRangeEXRangeFinalize;
    _kEXRangeClass.equal = __EXRangeEqual;
    _kEXRangeClass.hash = __EXRangeHash;
    _kEXRangeClass.copyFormattingDesc = __EXRangeCopyFormattingDesc;
    _kEXRangeClass.copyDebugDesc = __EXRangeCopyDebugDesc;
    _kEXRangeID = _CFRuntimeRegisterClass((const CFRuntimeClass * const)&_kEXRangeClass);
}

CFTypeID EXRangeGetTypeID(void) {
    return _kEXRangeID;
}

EXRangeRef EXRangeCreate(CFAllocatorRef allocator, uint32_t location, uint32_t length) {
    struct __EXRange *newrange;
    uint32_t extra = sizeof(struct __EXRange) - sizeof(CFRuntimeBase);
    newrange = (struct __EXRange *)_CFRuntimeCreateInstance(allocator, _kEXRangeID, extra, NULL);
    if (NULL == newrange) {
    return NULL;
    }
    newrange->_location = location;
    newrange->_length = length;
    return (EXRangeRef)newrange;
}

uint32_t EXRangeGetLocation(EXRangeRef rangeref) {
    return rangeref->_location;
}

uint32_t EXRangeGetLength(EXRangeRef rangeref) {
    return rangeref->_length;
}

#endif

Answer 2

CoreFoundation 本身不提供任何此类机制，但所有 Cocoa 对象都可以与 CFRetain 和 CFRelease 一起使用。所以唯一支持的答案是：创建一个基于 Foundation 的类，CoreFoundation 会将其识别为 CFTypeRef。