NSProxy

作者: 杰米 | 来源:发表于2017-02-08 17:58 被阅读153次

    objc与鸭子对象(上)
    分析"objc与鸭子对象"代码,该作者使用protocol实现一个模型的协议,使用NSProxy代理实现模型的存取值,十分巧妙,下面注释慢慢分析
    XXUserEntity.h

    //
    //  XXUserEntity.h
    //  XXDuckDemo
    //
    //  Created by sunnyxx on 14-8-27.
    //  Copyright (c) 2014年 sunnyxx. All rights reserved.
    //
    
    // 无需实体类,只需要协议
    @protocol XXUserEntity <NSObject>
    @property (nonatomic, copy) NSString *name;
    @property (nonatomic, copy) NSString *sex;
    @property (nonatomic, strong) NSNumber *age; // 要用基本类型需要实现自动拆装箱
    @end
    

    XXDuckEntity.h

    //
    //  XXDuckEntity.h
    //  XXDuckDemo
    //
    //  Created by sunnyxx on 14-8-16.
    //  Copyright (c) 2014年 sunnyxx. All rights reserved.
    //
    
    #import <Foundation/Foundation.h>
    
    @protocol XXDuckEntity <NSObject>
    @property (nonatomic, copy, readonly) NSString *jsonString;
    @end
    
    extern id/*<XXDuckEntity>*/ XXDuckEntityCreateWithJSON(NSString *json);
    

    XXDuckEntity.m

    //
    //  XXDuckEntity.m
    //  XXDuckDemo
    //
    //  Created by sunnyxx on 14-8-16.
    //  Copyright (c) 2014年 sunnyxx. All rights reserved.
    //
    
    #import "XXDuckEntity.h"
    
    
    @interface XXDuckEntity : NSProxy <XXDuckEntity>
    //将jsonString转成的字典,下面的消息转发会将setter和getter映射到这个字典!!十分关键的一个属性
    @property (nonatomic, strong) NSMutableDictionary *innerDictionary;
    @end
    
    @implementation XXDuckEntity
    //实现XXDuckEntity协议里的熟悉
    @synthesize jsonString = _jsonString;
    
    - (instancetype)initWithJSONString:(NSString *)json
    {
        if (json) {
            self->_jsonString = [json copy];
            NSData *data = [json dataUsingEncoding:NSUTF8StringEncoding];
            id jsonObject = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];
            if ([jsonObject isKindOfClass:[NSDictionary class]]) {
                self.innerDictionary = [jsonObject mutableCopy];
            }
            return self;
        }
        return nil;
    }
    
    #pragma mark - Message Forwading
    //消息转发流程 先methodSignatureForSelector:后forwardInvocation:,methodSignatureForSelector生成的签名会生成下面forwardInvocation的invocation
    
    - (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector
    {
        // Change method signature to NSMutableDictionary's
        // getter -> objectForKey:
        // setter -> setObject:forKey:
    
        SEL changedSelector = aSelector;
        /*
         为本类的用法,XXUserEntity作为一个协议其实只是骗过编译器而不报警告
         NSString *json = @"{\"name\": \"sunnyxx\", \"sex\": \"boy\", \"age\": 24}";
         id<XXDuckEntity, XXUserEntity> entity= XXDuckEntityCreateWithJSON(json);
         */
      //将setter和getter映射到字典
        if ([self propertyNameScanFromGetterSelector:aSelector]) {
            changedSelector = @selector(objectForKey:);
        }
        else if ([self propertyNameScanFromSetterSelector:aSelector]) {
            changedSelector = @selector(setObject:forKey:);
        }
        
        NSMethodSignature *sign = [[self.innerDictionary class] instanceMethodSignatureForSelector:changedSelector];
    
        return sign;
    }
    
    //NSInvocation是方法的封装,可以对方法参数设值
    - (void)forwardInvocation:(NSInvocation *)invocation
    {
        NSString *propertyName = nil;
    
        // Try getter
        propertyName = [self propertyNameScanFromGetterSelector:invocation.selector];
        if (propertyName) {
            invocation.selector = @selector(objectForKey:);
            [invocation setArgument:&propertyName atIndex:2]; // self, _cmd, key
            [invocation invokeWithTarget:self.innerDictionary];
            return;
        }
        
        // Try setter
        propertyName = [self propertyNameScanFromSetterSelector:invocation.selector];
        if (propertyName) {
            
            invocation.selector = @selector(setObject:forKey:);
            [invocation setArgument:&propertyName atIndex:3]; // self, _cmd, obj, key
            [invocation invokeWithTarget:self.innerDictionary];
            return;
        }
        
        [super forwardInvocation:invocation];
    }
    
    #pragma mark - Helpers
    
    - (NSString *)propertyNameScanFromGetterSelector:(SEL)selector
    {
        NSString *selectorName = NSStringFromSelector(selector);
        NSUInteger parameterCount = [[selectorName componentsSeparatedByString:@":"] count] - 1;
        if (parameterCount == 0) {
            return selectorName;
        }
        return nil;
    }
    
    - (NSString *)propertyNameScanFromSetterSelector:(SEL)selector
    {
        NSString *selectorName = NSStringFromSelector(selector);
        NSUInteger parameterCount = [[selectorName componentsSeparatedByString:@":"] count] - 1;
    
        if ([selectorName hasPrefix:@"set"] && parameterCount == 1) {
            NSUInteger firstColonLocation = [selectorName rangeOfString:@":"].location;
            return [selectorName substringWithRange:NSMakeRange(3, firstColonLocation - 3)].lowercaseString;
        }
        return nil;
    }
    
    @end
    
    id XXDuckEntityCreateWithJSON(NSString *json)
    {
        return [[XXDuckEntity alloc] initWithJSONString:json];
    }
    
    

    NSProxy——少见却神奇的类,利用NSProxy实现多继承
    Smart Proxy Delegation,外国大神写的NSProxy,用于简化delegate的的实现

    相关文章

      网友评论

          本文标题:NSProxy

          本文链接:https://www.haomeiwen.com/subject/fmzvittx.html