Runtime系列10之-Runtime的应用(三)

利用runtime 获取所有属性来重写归档解档方法

1. 我们先来看看基本的归档方法:

2. 假设现在有一个Movie类，有3个属性，它的.h.m文件这这样的:

    //Movie.h文件
    #import <Foundation/Foundation.h>
    //1. 如果想要当前类可以实现归档与反归档，需要遵守一个协议NSCoding
    @interface Movie : NSObject<NSCoding>
    @property (nonatomic, copy) NSString *movieId;
    @property (nonatomic, copy) NSString *movieName;
    @property (nonatomic, copy) NSString *pic_url;
    @end
       
    //Movie.m文件
    #import "Movie.h"
       
    @implementation Movie
    //必须实现这个方法,用于归档
    - (void)encodeWithCoder:(NSCoder *)aCoder
    {
        [aCoder encodeObject:_movieId forKey:@"id"];
        [aCoder encodeObject:_movieName forKey:@"name"];
        [aCoder encodeObject:_pic_url forKey:@"url"];
    }
    //必须实现这个方法用于解档
    - (id)initWithCoder:(NSCoder *)aDecoder
    {
        if (self = [super init]) {
            self.movieId = [aDecoder decodeObjectForKey:@"id"];
            self.movieName = [aDecoder decodeObjectForKey:@"name"];
            self.pic_url = [aDecoder decodeObjectForKey:@"url"];
        }
        return self;
    }
    @end
   

3. 如果这里有100个属性，那么我们也只能把100个属性都给写一遍。
4. 不过你会使用runtime后，这里就有更简便的方法。

5. 下面看看runtime的实现方式：

    #import "Movie.h"
    #import <objc/runtime.h>
    @implementation Movie
    - (void)encodeWithCoder:(NSCoder *)encoder
    {
        unsigned int count = 0;
        Ivar *ivars = class_copyIvarList([Movie class], &count);
        for (int i = 0; i<count; i++) {
            // 取出i位置对应的成员变量
            Ivar ivar = ivars[i];
            // 查看成员变量
            const char *name = ivar_getName(ivar);
            // 归档
            NSString *key = [NSString stringWithUTF8String:name];
            id value = [self valueForKey:key];
            [encoder encodeObject:value forKey:key];
        }
        free(ivars);
    }
    - (id)initWithCoder:(NSCoder *)decoder
    {
        if (self = [super init]) {
            unsigned int count = 0;
            Ivar *ivars = class_copyIvarList([Movie class], &count);
            for (int i = 0; i<count; i++) {
                // 取出i位置对应的成员变量
                Ivar ivar = ivars[i];
                // 查看成员变量
                const char *name = ivar_getName(ivar);
                // 归档
                NSString *key = [NSString stringWithUTF8String:name];
                id value = [decoder decodeObjectForKey:key];
                // 设置到成员变量身上
                [self setValue:value forKey:key];
            }
            free(ivars);
        }
        return self;
    }
    @end
   

6. 这样的方式实现，不管有多少个属性，写这几行代码就搞定了。怎么，还嫌麻烦，下面看看更加简便的方法：两句代码搞定。

7. 我们把encodeWithCoder 和 initWithCoder这两个方法抽成宏

    #import "Movie.h"
    #import <objc/runtime.h>
       
    #define encodeRuntime(A) \
    \
    unsigned int count = 0;\
    Ivar *ivars = class_copyIvarList([A class], &count);\
    for (int i = 0; i<count; i++) {\
    Ivar ivar = ivars[i];\
    const char *name = ivar_getName(ivar);\
    NSString *key = [NSString stringWithUTF8String:name];\
    id value = [self valueForKey:key];\
    [encoder encodeObject:value forKey:key];\
    }\
    free(ivars);\
    \
       
    #define initCoderRuntime(A) \
    \
    if (self = [super init]) {\
    unsigned int count = 0;\
    Ivar *ivars = class_copyIvarList([A class], &count);\
    for (int i = 0; i<count; i++) {\
    Ivar ivar = ivars[i];\
    const char *name = ivar_getName(ivar);\
    NSString *key = [NSString stringWithUTF8String:name];\
    id value = [decoder decodeObjectForKey:key];\
    [self setValue:value forKey:key];\
    }\
    free(ivars);\
    }\
    return self;\
    \
       
    @implementation Movie
       
    - (void)encodeWithCoder:(NSCoder *)encoder
       
    {
        encodeRuntime(Movie)
    }
       
    - (id)initWithCoder:(NSCoder *)decoder
    {
        initCoderRuntime(Movie)
    }
    @end
   

   我们可以把这两个宏单独放到一个文件里面，这里以后需要进行数据持久化的模型都可以直接使用这两个宏。

例2:

 // NSObject+Extension.h文件
 #import <Foundation/Foundation.h>
@interface NSObject (Extension)
- (NSArray *)ignoredNames;
- (void)encode:(NSCoder *)aCoder;
- (void)decode:(NSCoder *)aDecoder;
@end
 // NSObject+Extension.m文件
 #import "NSObject+Extension.h"
#import <objc/runtime.h>
@implementation NSObject (Extension)
- (void)decode:(NSCoder *)aDecoder {
    // 一层层父类往上查找，对父类的属性执行归解档方法
    Class c = self.class;
    while (c &&c != [NSObject class]) {
        unsigned int outCount = 0;
        Ivar *ivars = class_copyIvarList(c, &outCount);
        for (int i = 0; i < outCount; i++) {
            Ivar ivar = ivars[i];
            NSString *key = [NSString stringWithUTF8String:ivar_getName(ivar)];
            // 如果有实现该方法再去调用
            if ([self respondsToSelector:@selector(ignoredNames)]) {
                if ([[self ignoredNames] containsObject:key]) continue;
            }
            id value = [aDecoder decodeObjectForKey:key];
            [self setValue:value forKey:key];
        }
        free(ivars);
        c = [c superclass];
    }
}
- (void)encode:(NSCoder *)aCoder {
    // 一层层父类往上查找，对父类的属性执行归解档方法
    Class c = self.class;
    while (c &&c != [NSObject class]) {
        unsigned int outCount = 0;
        Ivar *ivars = class_copyIvarList([self class], &outCount);
        for (int i = 0; i < outCount; i++) {
            Ivar ivar = ivars[i];
            NSString *key = [NSString stringWithUTF8String:ivar_getName(ivar)];
            // 如果有实现该方法再去调用
            if ([self respondsToSelector:@selector(ignoredNames)]) {
                if ([[self ignoredNames] containsObject:key]) continue;
            }
            id value = [self valueForKeyPath:key];
            [aCoder encodeObject:value forKey:key];
        }
        free(ivars);
        c = [c superclass];
    }
}
@end

上面分类使用方法,在需要归解档的对象中实现下面方法即可：

// 设置需要忽略的属性
- (NSArray *)ignoredNames {
    return @[@"bone"];
}
// 在系统方法内来调用我们的方法
- (instancetype)initWithCoder:(NSCoder *)aDecoder {
    if (self = [super init]) {
        [self decode:aDecoder];
    }
    return self;
}
- (void)encodeWithCoder:(NSCoder *)aCoder {
    [self encode:aCoder];
}

这样看来，我们每次又要写同样的代码，我们可以将归解档两个方法封装为宏，在需要的地方一句宏搞定，如果有不需要归解档的属性就实现ignoredNames 方法