当我们需要将一个对象进行归档时，都要让该对象的类遵守NSCoding协议，再实现归档和接档方法。例如有一个Person类，该类有两个成员变量

@property (nonatomic,copy) NSString *name;@property (nonatomic,assign) int age;

两个协议的实现方法如下

/** *  将对象写入某个文件时需要调用，在该方法中说明哪些属性需要存储 */- (void)encodeWithCoder:(NSCoder *)encoder{    [encoder encodeObject:self.name forKey:@"name"];    [encoder encodeInt:self.age forKey:@"age"];}/** *  从文件中解析对象时会调用，在该方法中解析对象的属性 */- (id)initWithCoder:(NSCoder *)decoder{    if (self = [super init]) {        // 解析之后要赋值给属性        _name = [decoder decodeObjectForKey:@"name"];        _age = [decoder decodeIntForKey:@"age"];    }    return self;}

但当该类拥有上百个属性时，那将会花费更多的功夫在重复代码上，所以使用运行时机制截取类的成员变量，进行赋值

 

例如有一个狗类Dog和它的父类动物类Animal

狗类的成员变量有

@property (nonatomic,copy) NSString *name;@property (nonatomic,assign) int age;

 

动物类的成员变量有

@property (nonatomic,assign) double weight;

 

当我们需要将狗对象进行归档时，可以在类中这样重写归档和解档方法

- (id)initWithCoder:(NSCoder *)aDecoder{       if (self = [super init]) {        Class c = self.class;        // 截取类和父类的成员变量        while (c && c != [NSObject class]) {            unsigned int count = 0;            Ivar *ivars = class_copyIvarList(c, &count);            for (int i = 0; i < count; i++) {                               NSString *key = [NSString stringWithUTF8String:ivar_getName(ivars[i])];                               id value = [aDecoder decodeObjectForKey:key];                               [self setValue:value forKey:key];            }            // 获得c的父类            c = [c superclass];            free(ivar);        }                  }    return self;}- (void)encodeWithCoder:(NSCoder *)aCoder{        Class c = self.class;    // 截取类和父类的成员变量    while (c && c != [NSObject class]) {        unsigned int count = 0;               Ivar *ivars = class_copyIvarList(c, &count);               for (int i = 0; i < count; i++) {            Ivar ivar = ivars[i];            NSString *key = [NSString stringWithUTF8String:ivar_getName(ivar)];            id value = [self valueForKey:key];                       [aCoder encodeObject:value forKey:key];        }        c = [c superclass];        // 释放内存        free(ivar);    }   }

 

 代码测试：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{    CXDog *d = [[CXDogalloc] init];    d.name = @"cx";    d.age = 12;    d.weight = 1.55;    // 将对象归档    [NSKeyedArchiverarchiveRootObject:d toFile:@"/Users/c_xie/Desktop/wj.xxoo"];    // 将对象解档    CXDog *dog = [NSKeyedUnarchiverunarchiveObjectWithFile:@"/Users/c_xie/Desktop/wj.xxoo"];    NSLog(@"%@,%d,%f",dog.name,dog.age,d.weight);   }

以后就算有再多的属性，一个循环搞定