在使用keychain時，我們首先要將security.framework引入到工程中。由於使用時不支持arc，所以我們在arc環境中需要針對相關文件啟用mrc模式。
首先，我們構造壹個工具類，通過這個類來操作keychain。
#import
#import
@interface KeyChain : NSObject
// save username and password to keychain
+ (void)save:(NSString *)service data:(id)data;
// take out username and passwore from keychain
+ (id)load:(NSString *)service;
// delete username and password from keychain
+ (void)delete:(NSString *)service;
@end
在實現文件中，我們這樣寫：
#import "KeyChain.h"
@implementation KeyChain
/**
*該類需要工作在mrc模式下，acr的項目按照如下步驟操作
*選中工程->TARGETS->相應的target然後選中右側的“Build Phases”，向下就找到“Compile Sources”了。然後在相應的文件後面添加:-fno-objc-arc參數
*
**/
+ (NSMutableDictionary *)getKeychainQuery:(NSString *)service {
return [NSMutableDictionary dictionaryWithObjectsAndKeys:
(id)kSecClassGenericPassword,(id)kSecClass,
service, (id)kSecAttrService,
service, (id)kSecAttrAccount,
(id)kSecAttrAccessibleAfterFirstUnlock,(id)kSecAttrAccessible,
nil];
}
#pragma mark 寫入
+ (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);
}
#pragma mark 讀取
+ (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:(NSData *)keyData];
} @catch (NSException *e) {
NSLog(@"Unarchive of %@ failed: %@", service, e);
} @finally {
}
}
if (keyData)
CFRelease(keyData);
return ret;
}
#pragma mark 刪除
+ (void)delete:(NSString *)service {
NSMutableDictionary *keychainQuery = [self getKeychainQuery:service];
SecItemDelete((CFDictionaryRef)keychainQuery);
}
@end
修改工程的相關放在在代碼註釋中已經寫清楚了。
下邊是使用這個類
首先，我們定義幾個字符串類型的標識符
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";
之後，我們創建壹個字典，並將用戶名和密碼放入字典中
NSMutableDictionary *userNamePasswordKVPairs = [NSMutableDictionary dictionary];
[userNamePasswordKVPairs setObject:@"userName" forKey:KEY_USERNAME];
[userNamePasswordKVPairs setObject:@"password" forKey:KEY_PASSWORD];
下邊引用工具類的各個方法，分別進行用戶名和密碼的添加、讀取、刪除操作
// A、將用戶名和密碼寫入keychain
[KeyChain save:KEY_USERNAME_PASSWORD data:userNamePasswordKVPairs];
// B、從keychain中讀取用戶名和密碼
NSMutableDictionary *readUsernamePassword = (NSMutableDictionary *)[KeyChain load:KEY_USERNAME_PASSWORD];
NSString *userName = [readUsernamePassword objectForKey:KEY_USERNAME];
NSString *password = [readUsernamePassword objectForKey:KEY_PASSWORD];
NSLog(@"username = %@", userName);
NSLog(@"password = %@", password);
// C、將用戶名和密碼從keychain中刪除
[KeyChain delete:KEY_USERNAME_PASSWORD];
keychain的用法還有很多，我們在這裏只是簡單的將用戶名和密碼保存在keychain，而不是數據庫或nsuserdefaults中，以增加安全性。