iOS中链式编程最有名的莫过于Masonry了，以前就觉得Masonry的语法很好看，简单清楚明了，担得起“优雅”二字，那么这种链式编程的方法如何实现呢？在查询资料后，找到了一个小哥提供的案例，代码一眼就能让你了解链式编程。

先说理论，链式编程的特色在于连续的.语法，实现它，可以借助于Block：
利用类的getter特性，使得方法返回一个Block
Block中执行指定操作，并且返回该类的实例变量，以此实现连续的.语法

代码一看就会很清晰：

// UIButton+JWExtension.h
#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface UIButton (JWExtension)

+ (UIButton *)button;

// 设置默认状态标题
- (UIButton *(^)(NSString *))normalTitle;

// 设置选中状态标题
- (UIButton *(^)(NSString *))selectedTitle;

// 设置高亮状态标题
- (UIButton *(^)(NSString *))highlightTitle;

// 设置普通状态图片
- (UIButton *(^)(UIImage *))normalImage;

// 设置选中状态图片
- (UIButton *(^)(UIImage *))selectedImage;

// 设置高亮状态图片
- (UIButton *(^)(UIImage *))highlightedImage;

// 设置普通状态背景图片
- (UIButton *(^)(UIImage *))normalBackgroundImage;

// 设置高亮状态背景图片
- (UIButton *(^)(UIImage *))highlightedBackgroundImage;

// 设置选中状态背景图片
- (UIButton *(^)(UIImage *))selectedBackgroundImage;

@end


// UIButton+JWExtension.m
#import "UIButton+JWExtension.h"

@implementation UIButton (JWExtension)

+ (UIButton *)button{
    return [self buttonWithType:UIButtonTypeCustom];
}

- (UIButton * _Nonnull (^)(NSString * _Nonnull))normalTitle{
    return ^(NSString *title){
        [self setTitle:title forState:UIControlStateNormal];
        return self;
    };
}

- (UIButton *(^)(NSString *))selectedTitle {
    return ^(NSString *title){
        [self setTitle:title forState:UIControlStateNormal];
        return self;
    };
}

- (UIButton *(^)(NSString *))highlightTitle {
    return ^(NSString *title){
        [self setTitle:title forState:UIControlStateNormal];
        return self;
    };
}

- (UIButton *(^)(UIImage *))normalImage {
    return ^(UIImage *image){
        [self setImage:image forState:UIControlStateNormal];
        return self;
    };
}
- (UIButton *(^)(UIImage *))normalBackgroundImage {
    return ^(UIImage *image){
        [self setBackgroundImage:image forState:UIControlStateNormal];
        return self;
    };
}
- (UIButton *(^)(UIImage *))selectedImage {
    return ^(UIImage *image){
        [self setImage:image forState:UIControlStateSelected];
        return self;
    };
}

- (UIButton *(^)(UIImage *))selectedBackgroundImage {
    return ^(UIImage *image){
        [self setBackgroundImage:image forState:UIControlStateSelected];
        return self;
    };
}

- (UIButton *(^)(UIImage *))highlightedImage {
    return ^(UIImage *image){
        [self setImage:image forState:UIControlStateHighlighted];
        return self;
    };
}

- (UIButton *(^)(UIImage *))highlightedBackgroundImage {
    return ^(UIImage *image){
        [self setBackgroundImage:image forState:UIControlStateHighlighted];
        return self;
    };
}

@end


NS_ASSUME_NONNULL_END

这样就可以实现效果：

UIButton * btn = [UIButton button].normalTitle(@"Click").normalImage([UIImage imageNamed:@"button"]).selectedTitle(@"Clicked");

链式确实很优雅，不过Masonry不止有链式的优雅，还有很多牛逼的想法，改天出一篇Masonry源码的解析，膜拜一下大神。