iOS设计模式：备忘录

视频教程-极客学院

ps:感觉打的一手好广告啊，因为自己不太爱看视频，但这类又必须看才能明白。粘贴源代码是为了以后查阅方便，也注释了自己的理解。

需要有特定的key值去取得所需要的值。好比超市的存货柜类似，并且能存储任何对象的数据
自我认为实用与本地存储，对用户登录状态信息等进行必要存储就免得再次请求。

项目中需要引入：FastCoding （-nfo-objc-arc）

FastCoding-Github

MementoCenterProtocol

规定了协议，这个协议在Apple.h中体现

@protocol MementoCenterProtocol <NSObject>
@required
-(id)currentState;
-(void)recoverFromState:(id)state;

MementCenter

#import <Foundation/Foundation.h>
#import "MementoCenterProtocol.h"
@interface MementoCenter : NSObject

+ (void)saveMementoObject:(id <MementoCenterProtocol>)object withKey:(NSString *)key;
+ (id)mementoObjectWithKey:(NSString *)key;
@end

#import "MementoCenter.h"
#import "FastCoder.h"

@implementation MementoCenter
+ (void)saveMementoObject:(id <MementoCenterProtocol>)object withKey:(NSString *)key {
    NSParameterAssert(object);
    NSParameterAssert(key);

    // 获取data

    id      data    = [object currentState]; //按上面顺序是很难看明白这里上面意思，要去看Apple再看这里。
    NSData *tmpData = [FastCoder dataWithRootObject:data];

    // 进行存储

    if (tmpData) {
        [[NSUserDefaults standardUserDefaults] setObject:tmpData  forKey:key];
    }
}

+ (id)mementoObjectWithKey:(NSString *)key {
    NSParameterAssert(key);

    id     data    = nil;
    NSData *tmpData = [[NSUserDefaults standardUserDefaults] objectForKey:key];

    if (tmpData) {
        data = [FastCoder objectWithData:tmpData];
    }
    return data;
}
@end

MementoCenter

高度封装

#import <Foundation/Foundation.h>
@interface NSObject (MementoCenter)

/**
 *  存储状态
 *
 *  @param key 键值
 */
- (void)saveStateWithKey:(NSString *)key;

/**
 *  恢复状态
 *
 *  @param key 键值
 */
- (void)recoverFromStateWithKey:(NSString *)key;
@end

#import "NSObject+MementoCenter.h"
#import "MementoCenter.h"
@implementation NSObject (MementoCenter)
- (void)saveStateWithKey:(NSString *)key {
    NSParameterAssert(key);    

    id <MementoCenterProtocol> obj = (id <MementoCenterProtocol>)self;
    if ([obj respondsToSelector:@selector(currentState)]) {

   [MementoCenter saveMementoObject:obj withKey:key];
    }
}

- (void)recoverFromStateWithKey:(NSString *)key {
    NSParameterAssert(key);

    id                         state = [MementoCenter mementoObjectWithKey:key];
    id <MementoCenterProtocol> obj   = (id <MementoCenterProtocol>)self;
    if ([obj respondsToSelector:@selector(recoverFromStateWithKey:)]) {
        [obj recoverFromState:state];
    }
}

Apple

#import <Foundation/Foundation.h>
#import "MementoCenterProtocol.h"

@interface Apple : NSObject <MementoCenterProtocol>
@property (nonatomic, strong) NSString *name;
@property (nonatomic, strong) NSNumber *age;
@end

#import "Apple.h"

@implementation Apple
- (id)currentState {
    return @{@"name": self.name,
             @"age" : self.age};
}

- (void)recoverFromState:(id)state {

    NSDictionary *data = state;
    self.name = data[@"name"];
    self.age  = data[@"age"];
}
@end

使用

#import "ViewController.h"
#import "Apple.h"
#import "MementoCenter.h"
#import "NSObject+MementoCenter.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];
    Apple *apple = [[Apple alloc] init];
    apple.name = @"JiKeXueYuan";
    apple.age  = @(30);

  
//一般的使用方法
//    // save state 
//    [MementoCenter saveMementoObject:apple  withKey:@"Apple"];
//    

//    // get state
//    [apple recoverFromState:[MementoCenter mementoObjectWithKey:@"Apple"]];


//高度封装的使用方法
    [apple saveStateWithKey:@"Ben"];
    [apple recoverFromStateWithKey:@"Ben"];
    NSLog(@"name:%@ age:%@", apple.name, apple.age);

}

@end