NSAttributeString 链式编程：WZAttributedStringChain

富文本 NSAttributedString 在开发中经常用得到，虽然很实用，但是代码写起来却并不那么漂亮：

NSMutableAttributedString *mutableAttrStr = [[NSMutableAttributedString alloc] init];
[mutableAttrStr appendAttributedString:[[NSAttributedString alloc] initWithString:str1 attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:26], NSForegroundColorAttributeName:[UIColor redColor]}]];
[mutableAttrStr appendAttributedString:[[NSAttributedString alloc] initWithString:str2]];
[mutableAttrStr setAttributes:@{NSForegroundColorAttributeName:[UIColor yellowColor], NSBackgroundColorAttributeName:[UIColor lightGrayColor]} range:NSMakeRange(str1.length, 2)];
[mutableAttrStr appendAttributedString:[[NSAttributedString alloc] initWithString:str3 attributes:@{NSForegroundColorAttributeName:[UIColor blueColor], NSWritingDirectionAttributeName:@[@(NSWritingDirectionRightToLeft | NSWritingDirectionOverride)]}]];

看着不怎么美观。所以长久以来总是想要封装一下 NSAttributedString，但是又没什么好的思路。

这两天突然想起了链式编程这个词，琢磨着要不玩一下呗。

// BlockChainObject.h
@interface BlockChainObject : NSObject
@property (nonatomic, readonly) BlockChainObject *(^action)(void(^block)(void));
@end

// BlockChainObject.m
@interface BlockChainObject ()
@property (nonatomic, readwrite, copy) BlockChainObject *(^action)(void(^block)(void));
@end

@implementation BlockChainObject
- (instancetype)init {
	self = [super init];
	if (self) {
		__weak typeof(self) weak_self = self;
		self.action = ^BlockChainObject *(void(^block)(void)) {
			block();
			return weak_self;
		};
	}
	return self;
}
@end

// 调用
BlockChainObject *chainObj = [[BlockChainObject alloc] init];
chainObj.action(^{
	NSLog(@"1");
}).action(^{
	NSLog(@"2");
});

挺好玩诶
可是要怎么应用到 NSAttributedString 上呢？
我们的目标是消除 NSAttributedStringKey，专注于 value 上，让代码能像这样写：

attrStr.range(0, 2).attributes(...).range(3, 4).attributes(...)
以及
attrStr.attributes(...)

封装思路

WZAttributesBuilder

为了消除 NSAttributedStringKey，专注于 value，我们需要将 NSAttributedStringKey 封装起来。为此我们需要创建一个类来装载这些 value：WZAttributesBuilder。

@interface WZAttributesBuilder : NSObject

@property (nonatomic, strong) UIFont *font;						// 字体，默认 nil
@property (nonatomic, copy)   NSParagraphStyle *paragraphStyle; // 段落风格，默认 nil
@property (nonatomic, strong) UIColor *foregroundColor;			// 前景色（字体颜色），默认 nil
@property (nonatomic, strong) UIColor *backgroundColor;         // 背景色，默认 nil
@property (nonatomic, assign) BOOL ligature;					// 是否连字，默认 NO
@property (nonatomic, strong) NSNumber *kern;                   // 字符间距，默认 nil
@property (nonatomic, assign) NSUnderlineStyle strikethroughStyle;  // 删除线样式，默认 NSUnderlineStyleNone，没有删除线
@property (nonatomic, strong) UIColor *strikethroughColor;      // 删除线颜色，默认 nil
@property (nonatomic, assign) NSUnderlineStyle underlineStyle;  // 下划线样式，同删除线
@property (nonatomic, strong) UIColor *underlineColor;          // 下划线颜色，默认 nil
@property (nonatomic, strong) NSNumber *strokeWidth;            // 笔画宽度，默认 nil
@property (nonatomic, strong) UIColor *strokeColor;             // 笔画颜色，默认 nil
@property (nonatomic, strong) NSShadow *shadow;                 // 阴影样式，默认为 nil
@property (nonatomic, strong) NSTextEffectStyle textEffectStyle;// 特殊效果，默认为 nil
@property (nonatomic, strong) NSTextAttachment *attachment;     // 附件，默认 nil
@property (nonatomic, strong) NSURL *link;                      // 链接属性，默认为 nil
@property (nonatomic, strong) NSNumber *baselineOffset;         // 基线偏移量，默认 nil，正值上偏，负值下偏
@property (nonatomic, strong) NSNumber *obliqueness;            // 字体倾斜量，默认 nil，正值右倾，负值左倾
@property (nonatomic, strong) NSNumber *expansion;              // 字体的横向拉伸，默认 nil，正值拉伸，负值压缩
@property (nonatomic, assign) WZAttributedWriteDirection writeDirection;    // 文字书写方向，默认 WZAttributedWriteDirectionNone

//  根据属性的值生成字典@{NSAttributedStringKey: value}
- (NSDictionary<NSAttributedStringKey, id> *)attributes;

@end

// implementation 就不写出来了，有点长，github 地址在最下面。

这里需要提的是 NSWritingDirectionAttributeName（书写方向）的值，因为这个值需要是@[@(NSWritingDirection | NSWritingDirectionFormatType)] 的形式，所以我自定义了一个枚举来封装这些可能的值：

// 文字书写方向，详细:[NSWritingDirectionAttributeName](https://developer.apple.com/documentation/uikit/nswritingdirectionattributename)
typedef NS_ENUM(NSUInteger, WZAttributedWriteDirection) {
	WZAttributedWriteDirectionDefault, // 默认方向
	WZAttributedWriteDirectionLRE, // Left to Right, Embed
	WZAttributedWriteDirectionRLE, // Right to Left, Embed
	WZAttributedWriteDirectionLRO, // Left to Right, Override
	WZAttributedWriteDirectionRLO, // Right to Left, Override
};

测试之后发现只有 “Right to Left, Override” 的模式才能让书写方向由右往左书写，“Right to Left, Embed” 并不能达到这种效果。
苹果文档 对 NSWritingDirectionEmbedding 的解释：

Text is embedded in text with another writing direction. For example, an English quotation in the middle of an Arabic sentence could be marked as being embedded left-to-right text.
大概意思：一些文字以其他书写方向嵌入到一段文字中。比如一段阿拉伯文字中间嵌入一段英文文字，这段英文文字可以以从左向右的方向嵌入。

一开始没理解，查了一下阿拉伯文字的书写方向，发现是从右向左书写的。(= = )
虽然这么说，但是我并不知道该怎么测试 ⁄(⁄ ⁄•⁄ω⁄•⁄ ⁄)⁄

WZAttributeRange

有了封装 NSAttributedStringKey 的类了，就要开始构思如何做到attrStr.range(0, 2).attributes(...)。我们可以认为attrStr.attributes(...)是attrStr.range(0, attrStr.length).attributes(...)的简写形式。所以我们将围绕attrStr.range(0, 2).attributes(...)的形式来实现。

这里的问题只在于 range(0, 2) 应该返回什么值。1. 返回 NSAttributedString 对象，那么 NSAttributedString 对象需要保存一个 NSRange 变量；2. 返回一个第三方对象，那么这个对象需要保存一个 NSRange 变量，并实现 .attributes(...)；

我这里用了第二种方法，至于为什么，因为我是稀里糊涂就做了的 ⁄(⁄ ⁄•⁄ω⁄•⁄ ⁄)⁄。

因此我们创建 WZAttributeRange 类，具体实现：

// .h
typedef void(^WZBuildAttributesBlock)(WZAttributesBuilder *builder);
typedef NSAttributedString *(^WZAttributesBlock)(WZBuildAttributesBlock buildAttributes);

@interface WZAttributeRange : NSObject

- (instancetype)initWithAttributedString:(NSAttributedString *)attrStr range:(NSRange)range;

@property (nonatomic, readonly) WZAttributesBlock attributes;

@end

// .m
@interface WZAttributeRange ()
  
@property (nonatomic, strong) NSMutableAttributedString *mutableAttrStr;
@property (nonatomic, assign) NSRange range;
@property (nonatomic, readwrite, copy) WZAttributesBlock attributes;

@end

@implementation WZAttributeRange

- (instancetype)initWithAttributedString:(NSAttributedString *)attrStr range:(NSRange)range {
	if (self = [super init]) {
		self.mutableAttrStr = [attrStr mutableCopy];
		self.range = range;
		
		__weak typeof(self) weak_self = self;
		[self setAttributes:^NSAttributedString *(WZBuildAttributesBlock buildAttributes) {
			WZAttributesBuilder *builder = [[WZAttributesBuilder alloc] init];
			buildAttributes(builder);
			[weak_self.mutableAttrStr addAttributes:builder.attributes range:weak_self.range];
			return [weak_self.mutableAttrStr copy];
		}];
	}
	return self;
}

@end

这个类就这样，好像也没什么好说的了。需要注意的是，attributes()是用addAttributes 而不是 setAttributes。
可能存在的问题大概是调用链比较长的时候，会频繁创建 WZAttributeRange 和 WZAttributesBuilder 对象。

NSAttributedString(WZAttributeChain)

材料都准备好了，就可以开始对 NSAttributedString 动刀了。我们需要两个最基本的东西：range(loc, len) 和 attributes(...)，考虑到经常需要拼接其他 attributedString，所以加多一个append(attributedString)。

// .h
typedef WZAttributeRange *(^WZAttributeRangeBlock)(NSUInteger loc, NSUInteger len);
typedef NSAttributedString *(^WZAttributedAppendBlock)(NSAttributedString *attrStr);

@interface NSAttributedString (WZAttributeChain)

@property (nonatomic, readonly) WZAttributeRangeBlock range;
@property (nonatomic, readonly) WZAttributesBlock attributes;
@property (nonatomic, readonly) WZAttributedAppendBlock append;

@end

// .m
static const void *kWZAttributedStringRangeBlockKey = &kWZAttributedStringRangeBlockKey;
static const void *kWZAttributedStringAttributesBlockKey = &kWZAttributedStringAttributesBlockKey;
static const void *kWZAttributedStringAppendBlockKey = &kWZAttributedStringAppendBlockKey;

@implementation NSAttributedString (WZAttributeChain)

- (WZAttributeRangeBlock)range {
	WZAttributeRangeBlock range = objc_getAssociatedObject(self, kWZAttributedStringRangeBlockKey);
	if (!range) {
		__weak typeof(self) weak_self = self;
		range = ^WZAttributeRange *(NSUInteger loc, NSUInteger len){
			WZAttributeRange *range = [[WZAttributeRange alloc] initWithAttributedString:weak_self range:NSMakeRange(loc, len)];
			return range;
		};
		objc_setAssociatedObject(self, kWZAttributedStringRangeBlockKey, range, OBJC_ASSOCIATION_COPY_NONATOMIC);
	}
	return range;
}

- (WZAttributesBlock)attributes {
	WZAttributesBlock attributes = objc_getAssociatedObject(self, kWZAttributedStringAttributesBlockKey);
	if (!attributes) {
		__weak typeof(self) weak_self = self;
		attributes = ^NSAttributedString *(WZBuildAttributesBlock buildAttributes) {
			return weak_self.range(0, weak_self.length).attributes(buildAttributes);
		};
		objc_setAssociatedObject(self, kWZAttributedStringAttributesBlockKey, attributes, OBJC_ASSOCIATION_COPY_NONATOMIC);
	}
	return attributes;
}

- (WZAttributedAppendBlock)append {
	WZAttributedAppendBlock append = objc_getAssociatedObject(self, kWZAttributedStringAppendBlockKey);
	if (!append) {
		__weak typeof(self) weak_self = self;
		append = ^NSAttributedString *(NSAttributedString *attrStr) {
			NSMutableAttributedString *mutableAttrStr = [[NSMutableAttributedString alloc] initWithAttributedString:weak_self];
			[mutableAttrStr appendAttributedString:attrStr];
			return [mutableAttrStr copy];
		};
		objc_setAssociatedObject(self, kWZAttributedStringAppendBlockKey, append, OBJC_ASSOCIATION_COPY_NONATOMIC);
	}
	return append;
}

@end

这里也好像没什么好说的，就是通过 runtime 给 NSAttributedString 添加三个 block 属性，并且实现它们。
不过这里没有做线程安全，感觉没什么必要。

这里存在的问题是 attrStr1.attributes(...) return attrStr2 attrStr1 和 attrStr2 已经不是同一个对象了，这点要注意！

如果需要返回对象是原来的对象，就需要用到 NSMutableAttributedString 了。因为工作机制不一样，所以我们需要通过 NSMutableAttributedString 的分类 WZAttributeChain 重新实现这三个 block。不过代码都差不多，就不贴出来了。

集成 WZAttributedStringChain

pod ‘WZAttributedStringChain’

WZAttributedStringChain 使用方法

假设我们要在 label 上显示下图这段富文本，这也是最上面那段原生 NSAttributedString 的输出结果：

给定了三个字符串：

NSString *str1 = @"测试1", *str2 = @"测试2", *str3 = @"测试3";

// NSAttributedString(WZAttributeChain)
label.attributedText =
str1.attributedString.attributes(^(WZAttributesBuilder *builder) {
	builder.font = [UIFont systemFontOfSize:26];
	builder.foregroundColor = [UIColor redColor];
}).append(str2.attributedString.range(0, 2).attributes(^(WZAttributesBuilder *builder) {
	builder.foregroundColor = [UIColor yellowColor];
	builder.backgroundColor = [UIColor lightGrayColor];
})).append(str3.attributedString.attributes(^(WZAttributesBuilder *builder) {
	builder.foregroundColor = [UIColor blueColor];
	builder.writeDirection = WZAttributedWriteDirectionRLO;
}));

// NSMutableAttributedString(WZAttributeChain)
NSString *str = [NSString stringWithFormat:@"%@%@%@", str1, str2, str3];
label.attributedText =
str.mutableAttributedString.range(0, 3).attributes(^(WZAttributesBuilder *builder) {
	builder.font = [UIFont systemFontOfSize:26];
	builder.foregroundColor = [UIColor redColor];
}).range(3, 2).attributes(^(WZAttributesBuilder *builder) {
	builder.foregroundColor = [UIColor yellowColor];
	builder.backgroundColor = [UIColor lightGrayColor];
}).range(6, 3).attributes(^(WZAttributesBuilder *builder) {
	builder.foregroundColor = [UIColor blueColor];
	builder.writeDirection = WZAttributedWriteDirectionRLO;
});

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