那些年保存设备识别码keychainitemwrapper使用中的坑

突然间想到设备唯一识别码的事情，然后想研究一下，然后就在网上搜了许多资料，讲'keychainitemwrapper'的资料挺多的，但都大同小异，于是乎我选择了一篇文章按照方法来做，但是一直报错，按照这位仁兄的《iOS获取设备唯一标识码》文章一步步下来，结果报了下面的错误：

- (void)saveUuidWithKeyChain:(NSString *)uuid
{
    NSString *strUUID = [self.keychainItem objectForKey:(id)kSecValueData];
    if (strUUID == nil || strUUID.count==0)
    {
        [self.keychainItem setObject:uuid forKey:(id)kSecValueData];
    }
}

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后来打印了值，才发现原来取出来的数据不是 NSString，而是 NSArray:

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代码修改后

- (void)saveUuidWithKeyChain:(NSString *)uuid
{
    NSArray *strUUID = [self.keychainItem objectForKey:(id)kSecValueData]; // 此处不是NSString
    if (strUUID == nil || strUUID.count==0)
    {
        [self.keychainItem setObject:@[uuid] forKey:(id)kSecValueData]; // 存入的是数组类型
    }
}

问题解决了。
另外我有个问题一直没明白，一旦我初始化指定accessGroup参数，就会出错，设置为nil反而好了，请大神指教。

 self.keychainItem = [[KeychainItemWrapper alloc] initWithIdentifier:@"UUID" accessGroup:@"com.hp.uuidDemo"];

2017-02-24 11:55:39.010 UUIDDemo[685:210914] 21AF6998-21B2-4711-94B2-DA37EB4CDD48
2017-02-24 11:55:39.021 UUIDDemo[685:210914] *** Assertion failure in -[KeychainItemWrapper writeToKeychain], /Users/hp/workspaces/TYHS/UUIDDemo/UUIDDemo/KeychainItemWrapper.m:363
(lldb) 

以下是demo内容：

// 引入头文件
#import "ViewController.h"
#import 
#import "KeychainItemWrapper.h"
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UITextField *UUIDTextField;
/** uuid*/
@property (assign, nonatomic) long uuid;
/** KeychainItemWrapper*/
@property (strong, nonatomic) KeychainItemWrapper *keychainItem;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
   // 初始化
    self.keychainItem = [[KeychainItemWrapper alloc]
                                         initWithIdentifier:@"UUID" accessGroup:@"com.hp.uuidDemo"];
}
// 生成UUID
- (NSString *)getUUID{
    CFUUIDRef uuid = CFUUIDCreate(nil);
    CFStringRef uuidString = CFUUIDCreateString(nil, uuid);
    NSString *result = CFBridgingRelease(CFStringCreateCopy(NULL, uuidString));
    CFRelease(uuid);
    CFRelease(uuidString);
    return result;
}
- (IBAction)saveUUID:(UIButton *)sender {
    [self.keychainItem resetKeychainItem];
    NSString *uuid = [self getUUID];
    self.UUIDTextField.text = uuid;
    NSLog(@"%@", uuid);
    [self saveUuidWithKeyChain:uuid];
    // 0C3776B9-F6FA-430A-84F1-BC446B83A275
    // 
}
- (IBAction)readUUID:(UIButton *)sender {
    self.UUIDTextField.text = [self getKeychain];
    NSLog(@"%@", self.UUIDTextField.text);
}
// 保存UUID
- (void)saveUuidWithKeyChain:(NSString *)uuid
{
    NSArray *strUUID = [self.keychainItem objectForKey:(id)kSecValueData];
    if (strUUID == nil || strUUID.count==0)
    {
        [self.keychainItem setObject:@[uuid] forKey:(id)kSecValueData];
    }
}
// 获取保存在keychain中的UUID
- (NSString *)getKeychain {
    NSArray *strUUIDDArray = [self.keychainItem objectForKey:(id)kSecValueData];
    NSString *strUUID = strUUIDDArray.firstObject;
    return strUUID;
}

@end