ios - 什么会导致 NSUserDefaults 被清除

Question

我的应用程序收到一些奇怪的报告，其中存储在 NSUserDefaults 中的应用程序设置被清除。这些报告都在 iOS 7s 上

我知道您可以通过卸载或调用来手动清除 NSUserDefaults

NSString *appDomain = [[NSBundle mainBundle] bundleIdentifier];

[[NSUserDefaults standardUserDefaults] removePersistentDomainForName:appDomain];

但是否还有任何其他已知原因导致应用清除其设置？

Answer 1

如果您不想让您的数据被删除，那么您应该使用 KeyChain 来存储值。开始的好方法:Using KeyChain

下面我提供了一个示例代码，说明如何从 KeyChain 存储和获取数据

导入所需的框架

#import <Security/Security.h>

将值存储到 KeyChain

NSString *key = @"Full Name";
NSString *value = @"Steve Jobs";
NSData *valueData = [value dataUsingEncoding:NSUTF8StringEncoding];
NSString *service = [[NSBundle mainBundle] bundleIdentifier];
NSDictionary *secItem = @{
                              (__bridge id)kSecClass : (__bridge id)kSecClassGenericPassword, (__bridge id)kSecAttrService : service,
                              (__bridge id)kSecAttrAccount : key,
                              (__bridge id)kSecValueData : valueData,
                              };
    CFTypeRef result = NULL;
    OSStatus status = SecItemAdd((__bridge CFDictionaryRef)secItem, &result);
if (status == errSecSuccess)
{
     NSLog(@"Successfully stored the value");
}
else{
     NSLog(@"Failed to store the value with code: %ld", (long)status);
}

从 KeyChain 取回值

NSString *keyToSearchFor = @"Full Name";
NSString *service = [[NSBundle mainBundle] bundleIdentifier];
NSDictionary *query = @{
                        (__bridge id)kSecClass : (__bridge id)kSecClassGenericPassword, (__bridge id)kSecAttrService : service,(__bridge id)kSecAttrAccount : keyToSearchFor,
                        (__bridge id)kSecReturnAttributes : (__bridge id)kCFBooleanTrue, };
CFDictionaryRef valueAttributes = NULL;
OSStatus results = SecItemCopyMatching((__bridge CFDictionaryRef)query,
                                       (CFTypeRef *)&valueAttributes);
NSDictionary *attributes =
(__bridge_transfer NSDictionary *)valueAttributes;
if (results == errSecSuccess){
    NSString *key, *accessGroup, *creationDate, *modifiedDate, *service;
    key = attributes[(__bridge id)kSecAttrAccount];
    accessGroup = attributes[(__bridge id)kSecAttrAccessGroup]; creationDate = attributes[(__bridge id)kSecAttrCreationDate]; modifiedDate = attributes[(__bridge id)kSecAttrModificationDate]; service = attributes[(__bridge id)kSecAttrService];
    NSLog(@"Key = %@\n \ Access Group = %@\n \
          Creation Date = %@\n \
          Modification Date = %@\n \
          Service = %@", key, accessGroup, creationDate, modifiedDate, service);
}
else
{
    NSLog(@"Error happened with code: %ld", (long)results);
}