NSUserDefault用法

方法很简单，一行代码就可以搞定

//保存
- (void)saveValue:(NSString *)value forKey:(NSString *)key
{
    [[NSUserDefaults standardUserDefaults] setObject:value forKey:key];
}

//读取
- (void)readValueforKey:(NSString *)key
{
    [[NSUserDefaults standardUserDefaults] objectForKey:key];
}

注意

1. NSUserDefault只能保存特定类型的对象：NSData, NSString, NSNumber, NSDate, NSArray, NSDictionary。如果想要存储其它类型，需要将打包成NSData类型。
2. 如果保存其他类型的对象，会报错

   [User Defaults] Attempt to set a non-property-list object as an NSUserDefaults/CFPreferences value for key str

自定义Model打包NSData类型

1. 新建一个类Model，实现NSCoding协议
   Model.h

   #import 
   
   @interface Model : NSObject
   
   @property (nonatomic, copy) NSString *name;
   @property (nonatomic, copy) NSString *number;
   @property (nonatomic, assign) int user_id;
   
   @end
   

   Model.m

   #import "Model.h"
   
   @implementation Model
   
     - (void)encodeWithCoder:(nonnull NSCoder *)aCoder {
   [aCoder encodeObject:_name forKey:@"name"];
   [aCoder encodeObject:_number forKey:@"number"];
   [aCoder encodeObject:[NSNumber numberWithInt:_user_id] forKey:@"user_id"];
   }
   
   - (nullable instancetype)initWithCoder:(nonnull NSCoder *)aDecoder {
   self = [super init];
   if (self) {
       _name = [aDecoder decodeObjectForKey:@"name"];
       _number = [aDecoder decodeObjectForKey:@"number"];
       _user_id = [[aDecoder   decodeObjectForKey:@"user_id"] intValue];
       }
       return self;
   }
   @end
   

2. 在需要打包成NSData的地方

   //存数据
   NSData *data = [NSKeyedArchiver archivedDataWithRootObject:model];
   [[NSUserDefaults standardUserDefaults] setObject:data forKey:@"data"];
   
   //取数据
   NSData *daa = [[NSUserDefaults standardUserDefaults] objectForKey:@"data"];
   Model *newModel = [NSKeyedUnarchiver unarchiveObjectWithData:daa];