iOS删除App也无法删除的数据--keychain

由于苹果最近有了一些新动作，所以keychain这个功能可能没有办法做到iOS删除App也无法删除的数据，具体的内容可以看我最新的文章iOS 10.3 keychain 功能可能出现重大更改。

看标题是不是听起来挺唬人的，没错就是这么唬人，之前我没有发现iOS有这个功能，但是装了几个百度的应用之后我发现：卸载百度的应用之后，过段时间再次安装的时候你就会发现百度账号自动登录了，没错你可以去试试。看到这个现象之后我就寻求实现方法。下面贴出来：
iOS的keychain服务提供了一种安全的保存私密信息（密码，序列号，证书等）的方式。每个ios程序都有一个独立的keychain存储。从ios 3.0开始，跨程序分享keychain变得可行。
下面就使用keychain来实现存取用户名和密码。
苹果已经有现成的类封装好了keychain,KeychainItemWrapper.h和KeychainItemWrapper.m文件,可以在GenericKeychain实例里找到。
但是这里我只需要存取用户名和密码，就不用苹果提供的类了，自己写个简单的类来实现就好。
代码如下：
HPKeychain.h

#import <Foundation/Foundation.h>

@interface HPKeychain : NSObject

+ (void)save:(NSString *)service data:(id)data;
+ (id)load:(NSString *)service;
+ (void)delete:(NSString *)service;

@end

HPKeychain.m

#import "HPKeychain.h"

@implementation HPKeychain


+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service {
    return [NSMutableDictionary dictionaryWithObjectsAndKeys:
            (id)kSecClassGenericPassword,(id)kSecClass,
            service, (id)kSecAttrService,
            service, (id)kSecAttrAccount,
            (id)kSecAttrAccessibleAfterFirstUnlock,(id)kSecAttrAccessible,
            nil];
}

+ (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);
}




@end

使用方法

#import "ViewController.h"
#import "HPKeychain.h"


NSString * const KEY_USERNAME_PASSWORD = @"com.company.app.usernamepassword";
NSString * const KEY_USERNAME = @"com.company.app.username";
NSString * const KEY_PASSWORD = @"com.company.app.password";


@interface ViewController ()
@property (weak, nonatomic) IBOutlet UITextField *nameTextfield;
@property (weak, nonatomic) IBOutlet UITextField *passwordTextField;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    //从keychain中取出用户名和密码：
    NSMutableDictionary *usernamepasswordKVPairs = (NSMutableDictionary *)[HPKeychain load:KEY_USERNAME_PASSWORD];
    _nameTextfield.text = [usernamepasswordKVPairs objectForKey:KEY_USERNAME];
    _passwordTextField.text = [usernamepasswordKVPairs objectForKey:KEY_PASSWORD];
}
- (IBAction)saveAction:(UIButton *)sender {
    //把用户名和密码存入keychain：
    NSMutableDictionary *usernamepasswordKVPairs = [NSMutableDictionary dictionary];
    [usernamepasswordKVPairs setObject:_nameTextfield.text forKey:KEY_USERNAME];
    [usernamepasswordKVPairs setObject:_passwordTextField.text forKey:KEY_PASSWORD];
    [HPKeychain save:KEY_USERNAME_PASSWORD data:usernamepasswordKVPairs];
    
    
    UIAlertController * alert = [UIAlertController alertControllerWithTitle:@"提示" message:@"保存成功" preferredStyle:UIAlertControllerStyleAlert];
    UIAlertAction * action = [UIAlertAction actionWithTitle:@"我知道了" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
        NSLog(@"点击了确认");
    }];
    [alert addAction:action];
    [self presentViewController:alert animated:YES completion:nil];
}


- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

删除一个keychain item:
[HPKeychain delete:KEY_USERNAME_PASSWORD];

这里可以查看代码