投間接指針的一個Objective-C的指針

Question

我有以下代碼：

OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef)attrDictionary, (CFTypeRef *)&value); 

導致的錯誤：

Implicit conversion of an indirect pointer to an Objective-C pointer to 'CFTypeRef *' (aka 'const void **') is disallowed with ARC 

關於如何解決此問題的任何想法？我試圖改變CFTypeRef *到id *，但它沒有工作

下面是完整的方法：

+ (NSData *)keychainValueForKey:(NSString *)key { 
    if (key == nil) { 
    return nil; 
    } 

    NSMutableDictionary *attrDictionary = [self attributesDictionaryForKey:key]; 

    // Only want one match 
    [attrDictionary setObject:(id)kSecMatchLimitOne forKey:(id)kSecMatchLimit]; 

    // Only one value being searched only need a bool to tell us if it was successful 
    [attrDictionary setObject:(id)kCFBooleanTrue forKey:(id)kSecReturnData]; 

    NSData *value = nil; 
    OSStatus status = SecItemCopyMatching((CFDictionaryRef)attrDictionary, (CFTypeRef *)&value); 
    if (status != errSecSuccess) { 
    DLog(@"KeychainUtils keychainValueForKey: - Error finding keychain value for key. Status code = %d", status); 
    } 
    return [value autorelease]; 
} 

Answer 1

你只需將它轉換爲void *：

OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef)attrDictionary, 
    (void *)&value); 

如果你使用Objective-C++，您可能必須將其投射兩次：

OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef)attrDictionary, 
    (CFTypeRef *)(void *)&value); 

或者您可以使用臨時變量：

CFTypeRef cfValue = NULL; 
OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef)attrDictionary, &cfValue); 
NSData *value = (__bridge id)cfValue;