前言

最近对Masonry的链式句法很感兴趣,于是尝试自己实现该效果.我是做了一个加法器,用法如下:

int result = [NSObject makeCaculator:^(CaculatorMaker *make) {
      make.add(2).add(4);
    }];
    NSLog(@"result is %d", result);

打印结果:

2016-02-20 15:18:17.178 练习链式语法封装[30206:1952288] result is 6

思路

实现链式句法主要原理是利用OC的block特性,add是make对象的一个block属性,定义如下:

@property (copy, nonatomic, readonly) CaculatorMaker *(^add)(int);

该block属性以block的形式被调用时,会用到一个int参数,返回一个CaculatorMaker对象(其实是返回的self),然后返回的CaculatorMaker对象可以再次调用自己的add属性,从而达到链式句法的效果

具体实现

NSObject+Caculator.h 文件

#import <Foundation/Foundation.h>
@class CaculatorMaker;
//NSObject类的拓展
@interface NSObject (Caculator)
+ (int)makeCaculator:(void (^)(CaculatorMaker *make)) caculatorBlock;

@end

//CaculatorMaker类的声明
@interface CaculatorMaker : NSObject
@property (assign, nonatomic) int result;
@property (copy, nonatomic, readonly) CaculatorMaker *(^add)(int);

@end

NSObject+Caculator.m 文件

#import "NSObject+Caculator.h"

@implementation NSObject (Caculator)

+ (int)makeCaculator:(void (^)(CaculatorMaker *))caculatorBlock {
    CaculatorMaker *make = [CaculatorMaker new];
    caculatorBlock(make);
    return make.result;
}

@end

@implementation CaculatorMaker

- (instancetype)init
{
    self = [super init];
    if (self) {
        self.result = 0;
    }
    return self;
}

- (CaculatorMaker *(^)(int))add {
    return ^(int a){
        self.result += a;
        return self;
    };
}

@end