将间接指针强制转换为 Objective-C 指针

Posted 2023-03-12

【中文标题】将间接指针强制转换为 Objective-C 指针

【英文标题】：cast of indirect pointer to an Objective-C pointer

【发布时间】：2012-09-13 18:27:31

【问题描述】：

我有以下代码：

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

导致错误：

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

关于如何解决这个问题的任何想法？我尝试将CFTypeRef * 更改为id *，但没有成功

这是完整的方法：

+ (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];

【参考方案1】：

您可以将其转换为 void *:

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

如果您使用的是 Objective-C++，您可能需要转换两次：

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

或者你可以使用一个临时变量：

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