Runtime应用（三）实现NSCoding的自动归档和自动解档

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