指向Objective-C指針的間接指針的強制轉換

Question

我有以下代碼：

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

這導致錯誤：

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

有關如何解決此問題的任何想法？ 我已經嘗試將CFTypeRef *更改為id *但它沒有成功

這是完整的方法：

+ (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

您可以將其void *為void * ：

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

如果您使用的是Objective-C ++，則可能需要將其強制轉換兩次：

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;