利用runtime序列化对象

方法一

编解码的核心就是:遍历该类的属性变量、实例变量及其父类的属性变量（父类的实例变量为其私有，我们如果对其进行编解码会崩溃）,这时候就用到运行时的api了

敲重点：

Class cls = [self class];
BOOL isSelfClass = (cls == [self class]);

objc_property_t *propertyList = isSelfClass ? NULL : class_copyPropertyList(cls, &propertyCount);
Ivar *ivarList = isSelfClass ? class_copyIvarList(cls, &iVarCount) :NULL;

解释一下，首先判断是不是本类，如果是本类，就使用class_copyIvarList获取属性变量和实例变量；

如果是父类，就使用class_copyIvarList获取父类的属性变量。

//解码
- (id)initWithCoder:(NSCoder *)coder
{
    Class cls = [self class]; while (cls != [NSObject class]) {
        BOOL isSelfClass = (cls == [self class]);
        unsigned int iVarCount = 0;
        unsigned int propertyCount = 0;

        objc_property_t *propertyList = isSelfClass ? NULL : class_copyPropertyList(cls, &propertyCount);
        Ivar *ivarList =  isSelfClass ? class_copyIvarList(cls, &iVarCount) :NULL;

        unsigned int finalCount = isSelfClass ? iVarCount : propertyCount; for (int i = 0; i < finalCount; i++) { const char * varName = isSelfClass ? ivar_getName(*(ivarList + i)) :property_getName(*(propertyList + i));//取得变量名字，将作为key
            NSString *key = [NSString stringWithUTF8String:varName]; //decode
            id  value = [coder decodeObjectForKey:key];//解码
            NSArray *filters = @[@"superclass", @"description", @"debugDescription", @"hash"]; if (value && [filters containsObject:key] == NO) {
                [self setValue:value forKey:key];//使用KVC强制写入到对象中
 }
        }
        free(ivarList);//记得释放内存
 free(propertyList);
        cls = class_getSuperclass(cls);
    } return self;

}

//编码
- (void)encodeWithCoder:(NSCoder *)coder
{
    Class cls = [self class]; while (cls != [NSObject class]) {
        BOOL isSelfClass = (cls == [self class]);
        unsigned int varCount = 0;
        unsigned int properCount = 0;
        Ivar *ivarList = isSelfClass ? class_copyIvarList([self class], &varCount) : NULL;
        objc_property_t *propertyList = isSelfClass ? NULL : class_copyPropertyList(cls, &properCount);

        unsigned int finalCount = isSelfClass ? varCount : properCount; for (int i = 0; i < finalCount; i++) { const char *varName = isSelfClass ? ivar_getName(*(ivarList + i)) : property_getName(*(propertyList + i));
            NSString *key = [NSString stringWithUTF8String:varName]; id varValue = [self valueForKey:key];//使用KVC获取key对应的变量值
            NSArray *filters = @[@"superclass", @"description", @"debugDescription", @"hash"]; if (varValue && [filters containsObject:key] == NO) {
                [coder encodeObject:varValue forKey:key];
            }
        }
        free(ivarList);
        free(propertyList);
        cls = class_getSuperclass(cls);
    }

}

另外，为一个类添加描述也可以同理进行处理,这样就可以很直观的看出容器里装的model类是怎样子的了:

/* 用来打印本类的所有变量(成员变量+属性变量)，所有层级父类的属性变量及其对应的值 */  
- (NSString *)description
{   
    NSString *despStr = @"";   
    Class cls = [self class]; while (cls != [NSObject class]) { /*判断是自身类还是父类*/ BOOL bIsSelfClass = (cls == [self class]);  
        unsigned int iVarCount = 0; 
        unsigned int propVarCount = 0;  
        unsigned int sharedVarCount = 0;    
        Ivar *ivarList = bIsSelfClass ? class_copyIvarList([cls class], &iVarCount) : NULL;/*变量列表，含属性以及私有变量*/ objc_property_t *propList = bIsSelfClass ? NULL : class_copyPropertyList(cls, &propVarCount);/*属性列表*/ sharedVarCount = bIsSelfClass ? iVarCount : propVarCount; for (int i = 0; i < sharedVarCount; i++) { const char *varName = bIsSelfClass ? ivar_getName(*(ivarList + i)) : property_getName(*(propList + i)); 
            NSString *key = [NSString stringWithUTF8String:varName]; /*valueForKey只能获取本类所有变量以及所有层级父类的属性，不包含任何父类的私有变量(会崩溃)*/  
            id varValue = [self valueForKey:key];   
            NSArray *filters = @[@"superclass", @"description", @"debugDescription", @"hash"]; if (varValue && [filters containsObject:key] == NO) { 
                despStr = [despStr stringByAppendingString:[NSString stringWithFormat:@"%@: %@n", key, varValue]]; 
            }   
        }   
        free(ivarList); 
        free(propList); 
        cls = class_getSuperclass(cls); 
    } return despStr; 
}

方法二

其实作为归档来说，我们通常不需要讲父类全部属性一起归档。只需要通过解档来去除我们所需的数据、状态。因此以下为常用的更为简洁的代码：

#import "Student.h"
#import <objc/runtime.h>
#import <objc/message.h>

@implementation Student

- (void)encodeWithCoder:(NSCoder *)aCoder{
    unsigned int outCount = 0;
    Ivar *vars = class_copyIvarList([self class], &outCount);
    for (int i = 0; i < outCount; i ++) {
        Ivar var = vars[i];
        const char *name = ivar_getName(var);
        NSString *key = [NSString stringWithUTF8String:name];

        id value = [self valueForKey:key];
        [aCoder encodeObject:value forKey:key];
    }
}

- (nullable __kindof)initWithCoder:(NSCoder *)aDecoder{
    if (self = [super init]) {
        unsigned int outCount = 0;
        Ivar *vars = class_copyIvarList([self class], &outCount);
        for (int i = 0; i < outCount; i ++) {
            Ivar var = vars[i];
            const char *name = ivar_getName(var);
            NSString *key = [NSString stringWithUTF8String:name];
            id value = [aDecoder decodeObjectForKey:key];
            [self setValue:value forKey:key];
        }
    }
    return self;
}
@end

在此基础上，也可以利用继承，去先执行super的encode方法，在父类的该方法中去处理父类的属性，子类中处理子类的属性更为清晰。