基于钥匙串的保存

封装了一些存储入钥匙串的方法。这个方法与本地存储的区别是什么呢？查看了大部分的文档解读，我觉得就是：
1.不易丢失。如果项目迭代更新、重装等等。存储的本地内容将不会存在。而钥匙串中的数据还能保存。
2.破解难度大。其他的本地存储截取更简单一些，所以用户名密码存储做的好点最好是不要放入本地存储中。加密放入钥匙串更加不易破解。

---

封装：
1.在Capabilities中勾选Keychain Sharing.
2.创建一个文件用于封装。
这里的封装适合保存一个值。多个值的封装需要传入保存的Key。
3.方法创建：

/**
 *  存储字符串到 KeyChain
 *
 *  @param string NSString
 */
+ (void)keyChainSave:(NSString *)string;

/**
 *  从 KeyChain 中读取存储的字符串
 *
 *  @return NSString
 */
+ (NSString *)keyChainLoad;

/**
 *  删除 KeyChain 信息
 */
+ (void)keyChainDelete;

4.方法实现

static NSString * const kPDDictionaryKey = @"com.xxx.dictionaryKey";
static NSString * const kPDKeyChainKey = @"com.xxx.keychainKey";

+ (void)keyChainSave:(NSString *)string {
    NSMutableDictionary *tempDic = [NSMutableDictionary dictionary];
    [tempDic setObject:string forKey:kPDDictionaryKey];
    [self save:kPDKeyChainKey data:tempDic];
}

+ (NSString *)keyChainLoad{
    NSMutableDictionary *tempDic = (NSMutableDictionary *)[self load:kPDKeyChainKey];
    return [tempDic objectForKey:kPDDictionaryKey];
}

+ (void)keyChainDelete{
    [self delete:kPDKeyChainKey];
}

---

内部方法

+ (void)save:(NSString *)service data:(id)data {
    //Get search dictionary
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
    //Delete old item before add new item
    SecItemDelete((CFDictionaryRef)keychainQuery);
    //Add new object to search dictionary(Attention:the data format)
    [keychainQuery setObject:[NSKeyedArchiver archivedDataWithRootObject:data] forKey:(id)kSecValueData];
    //Add item to keychain with the search dictionary
    SecItemAdd((CFDictionaryRef)keychainQuery, NULL);
}

+ (id)load:(NSString *)service {
    id ret = nil;
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
    //Configure the search setting
    //Since in our simple case we are expecting only a single attribute to be returned (the password) we can set the attribute kSecReturnData to kCFBooleanTrue
    [keychainQuery setObject:(id)kCFBooleanTrue forKey:(id)kSecReturnData];
    [keychainQuery setObject:(id)kSecMatchLimitOne forKey:(id)kSecMatchLimit];
    CFDataRef keyData = NULL;
    if (SecItemCopyMatching((CFDictionaryRef)keychainQuery, (CFTypeRef *)&keyData) == noErr) {
        @try {
            ret = [NSKeyedUnarchiver unarchiveObjectWithData:(__bridge NSData *)keyData];
        } @catch (NSException *e) {
            NSLog(@"Unarchive of %@ failed: %@", service, e);
        } @finally {
        }
    }
    if (keyData)
        CFRelease(keyData);
    return ret;
}

+ (void)delete:(NSString *)service {
    NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
    SecItemDelete((CFDictionaryRef)keychainQuery);
}

---

使用：

// 存
- (void)saveUseAccount {
        [PDKeyChain keyChainSave:self.userNameTextField.text];
}
// 读取
  // 从keychain里取账号信息
    self.userNameTextField.text = [PDKeyChain keyChainLoad];

ps：中间内容参考别人的，但是出处没有查到了。只是个人记录以后使用。