目前市面上的非UI線(xiàn)程文本算高方法或多或少都有一些問(wèn)題。本文通過(guò)逆向和分析UILabel的sizeThatFits方法實(shí)現(xiàn)來(lái)得到一個(gè)最佳的文本算高的精簡(jiǎn)方法。方法可以運(yùn)行在任意線(xiàn)程，因此可以有效的應(yīng)用在那些異步算高或者要求尺寸進(jìn)行提前計(jì)算的場(chǎng)景中。

從iOS官方的實(shí)現(xiàn)中可以看出文本算高會(huì)考慮簡(jiǎn)單文本字符串、屬性字符串、字體大小、最大顯示行數(shù)numberOfLines、段落信息、 段落的對(duì)齊方式、斷字方式、段落的首行縮進(jìn)、陰影偏移等等因素。下面就是具體的實(shí)現(xiàn)代碼：

/// 使用此方法時(shí)請(qǐng)標(biāo)明源作者：歐陽(yáng)大哥2013。本方法符合MIT協(xié)議規(guī)范。
/// github地址：https://github.com/youngsoft
/// 計(jì)算簡(jiǎn)單文本或者屬性字符串的自適應(yīng)尺寸
/// @param fitsSize 指定限制的尺寸，參考UILabel中的sizeThatFits中的參數(shù)的意義。
/// @param text 要計(jì)算的簡(jiǎn)單文本NSString或者屬性字符串NSAttributedString對(duì)象
/// @param numberOfLines 指定最大顯示的行數(shù)，如果為0則表示不限制最大行數(shù)
/// @param font 指定計(jì)算時(shí)文本的字體，可以為nil表示使用UILabel控件的默認(rèn)17號(hào)字體
/// @param textAlignment 指定文本對(duì)齊方式默認(rèn)是NSTextAlignmentNatural
/// @param lineBreakMode 指定多行時(shí)斷字模式，默認(rèn)可以用UILabel的默認(rèn)斷字模式NSLineBreakByTruncatingTail
/// @param minimumScaleFactor 指定文本的最小縮放因子，默認(rèn)填寫(xiě)0。這個(gè)參數(shù)用于那些定寬時(shí)可以自動(dòng)縮小文字字體來(lái)自適應(yīng)顯示的場(chǎng)景。
/// @param shadowOffset 指定陰影的偏移位置，需要注意的是這個(gè)偏移位置是同時(shí)指定了陰影顏色和偏移位置才有效。如果不考慮陰影則請(qǐng)傳遞CGSizeZero，否則陰影會(huì)參與尺寸計(jì)算。
/// @return 返回自適應(yīng)的最合適尺寸
CGSize calcTextSize(CGSize fitsSize, id text, NSInteger numberOfLines, UIFont *font, NSTextAlignment textAlignment, NSLineBreakMode lineBreakMode, CGFloat minimumScaleFactor, CGSize shadowOffset) {
    
    if (text == nil || [text length] <= 0) {
        return CGSizeZero;
    }
    
    NSAttributedString *calcAttributedString = nil;

    //如果不指定字體則用默認(rèn)的字體。
    if (font == nil) {
        font = [UIFont systemFontOfSize:17];
    }
    
    CGFloat systemVersion = [UIDevice currentDevice].systemVersion.floatValue;
        
    NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
    paragraphStyle.alignment = textAlignment;
    paragraphStyle.lineBreakMode = lineBreakMode;
    //系統(tǒng)大于等于11才設(shè)置行斷字策略。
    if (systemVersion >= 11.0) {
        @try {
            [paragraphStyle setValue:@(1) forKey:@"lineBreakStrategy"];
        } @catch (NSException *exception) {}
    }
        
    if ([text isKindOfClass:NSString.class]) {
        calcAttributedString = [[NSAttributedString alloc] initWithString:(NSString *)text attributes:@{NSFontAttributeName:font, NSParagraphStyleAttributeName:paragraphStyle}];
    } else {
        NSAttributedString *originAttributedString = (NSAttributedString *)text;
        //對(duì)于屬性字符串總是加上默認(rèn)的字體和段落信息。
        NSMutableAttributedString *mutableCalcAttributedString = [[NSMutableAttributedString alloc] initWithString:originAttributedString.string attributes:@{NSFontAttributeName:font, NSParagraphStyleAttributeName:paragraphStyle}];
        
        //再附加上原來(lái)的屬性。
        [originAttributedString enumerateAttributesInRange:NSMakeRange(0, originAttributedString.string.length) options:0 usingBlock:^(NSDictionary<NSAttributedStringKey,id> * _Nonnull attrs, NSRange range, BOOL * _Nonnull stop) {
            [mutableCalcAttributedString addAttributes:attrs range:range];
        }];
        
        //這里再次取段落信息，因?yàn)橛锌赡軐傩宰址芯鸵呀?jīng)包含了段落信息。
        if (systemVersion >= 11.0) {
            NSParagraphStyle *alternativeParagraphStyle = [mutableCalcAttributedString attribute:NSParagraphStyleAttributeName atIndex:0 effectiveRange:NULL];
            if (alternativeParagraphStyle != nil) {
                paragraphStyle = (NSMutableParagraphStyle*)alternativeParagraphStyle;
            }
        }
        
        calcAttributedString = mutableCalcAttributedString;
    }
    
    //調(diào)整fitsSize的值, 這里的寬度調(diào)整為只要寬度小于等于0或者顯示一行都不限制寬度，而高度則總是改為不限制高度。
    fitsSize.height = FLT_MAX;
    if (fitsSize.width <= 0 || numberOfLines == 1) {
        fitsSize.width = FLT_MAX;
    }
        
    //構(gòu)造出一個(gè)NSStringDrawContext
    NSStringDrawingContext *context = [[NSStringDrawingContext alloc] init];
    context.minimumScaleFactor = minimumScaleFactor;
    @try {
        //因?yàn)橄旅鎺讉€(gè)屬性都是未公開(kāi)的屬性，所以我們用KVC的方式來(lái)實(shí)現(xiàn)。
        [context setValue:@(numberOfLines) forKey:@"maximumNumberOfLines"];
        if (numberOfLines != 1) {
            [context setValue:@(YES) forKey:@"wrapsForTruncationMode"];
        }
        [context setValue:@(YES) forKey:@"wantsNumberOfLineFragments"];
    } @catch (NSException *exception) {}
       

    //計(jì)算屬性字符串的bounds值。
    CGRect rect = [calcAttributedString boundingRectWithSize:fitsSize options:NSStringDrawingUsesLineFragmentOrigin context:context];
    
    //需要對(duì)段落的首行縮進(jìn)進(jìn)行特殊處理！
    //如果只有一行則直接添加首行縮進(jìn)的值，否則進(jìn)行特殊處理。。
    CGFloat firstLineHeadIndent = paragraphStyle.firstLineHeadIndent;
    if (firstLineHeadIndent != 0.0 && systemVersion >= 11.0) {
        //得到繪制出來(lái)的行數(shù)
        NSInteger numberOfDrawingLines = [[context valueForKey:@"numberOfLineFragments"] integerValue];
        if (numberOfDrawingLines == 1) {
            rect.size.width += firstLineHeadIndent;
        } else {
            //取內(nèi)容的行數(shù)。
            NSString *string = calcAttributedString.string;
            NSCharacterSet *charset = [NSCharacterSet newlineCharacterSet];
            NSArray *lines = [string componentsSeparatedByCharactersInSet:charset]; //得到文本內(nèi)容的行數(shù)
            NSString *lastLine = lines.lastObject;
            NSInteger numberOfContentLines = lines.count - (NSInteger)(lastLine.length == 0);  //有效的內(nèi)容行數(shù)要減去最后一行為空行的情況。
            if (numberOfLines == 0) {
                numberOfLines = NSIntegerMax;
            }
            if (numberOfLines > numberOfContentLines)
                numberOfLines = numberOfContentLines;
            
            //只有繪制的行數(shù)和指定的行數(shù)相等時(shí)才添加上首行縮進(jìn)！這段代碼根據(jù)反匯編來(lái)實(shí)現(xiàn)，但是不理解為什么相等才設(shè)置？
            if (numberOfDrawingLines == numberOfLines) {
                rect.size.width += firstLineHeadIndent;
            }
        }
    }
    
    //取fitsSize和rect中的最小寬度值。
    if (rect.size.width > fitsSize.width) {
        rect.size.width = fitsSize.width;
    }
    
    //加上陰影的偏移
    rect.size.width += fabs(shadowOffset.width);
    rect.size.height += fabs(shadowOffset.height);
       
    //轉(zhuǎn)化為可以有效顯示的邏輯點(diǎn), 這里將原始邏輯點(diǎn)乘以縮放比例得到物理像素點(diǎn)，然后再取整，然后再除以縮放比例得到可以有效顯示的邏輯點(diǎn)。
    CGFloat scale = [UIScreen mainScreen].scale;
    rect.size.width = ceil(rect.size.width * scale) / scale;
    rect.size.height = ceil(rect.size.height *scale) / scale;
    
    return rect.size;
}

//上述方法的精簡(jiǎn)版本
NS_INLINE CGSize calcTextSizeV2(CGSize fitsSize, id text, NSInteger numberOfLines, UIFont *font) {
    return calcTextSize(fitsSize, text, numberOfLines, font, NSTextAlignmentNatural, NSLineBreakByTruncatingTail,0.0, CGSizeZero);
}

下面是具體的驗(yàn)證測(cè)試用例(用例在iOS9到iOS13上運(yùn)行通過(guò))：

   CFTimeInterval simpleTextUILabelInterval = 0;
    CFTimeInterval simpleTextNOUILabelInterval = 0;
    CFTimeInterval attributedTextUILabelInterval = 0;
    CFTimeInterval attributedTextNOUILabelInterval = 0;
    NSArray *testStringArray = @[@"您",@"好",@"中",@"國(guó)",@"w",@"i",@"d",@"t",@"h",@",",@"。",@"a",@"b",@"c",@"\n", @"1",@"5",@"2",@"j",@"A",@"J",@"0",@"??",@"??",@" "];
    srand(time(NULL));
    for (int i = 0; i < 5000; i++) {
        //隨機(jī)生成0到100個(gè)字符。
        int textLength = rand() % 100;
        NSMutableString *text = [NSMutableString new];
        for (int j = 0; j < textLength; j++) {
            [text appendString:testStringArray[rand()%testStringArray.count]];
        }
        if (text.length == 0)
            continue;
        
        CGSize fitSize = CGSizeMake(rand()%1000, rand()%1000);
        
        //測(cè)試簡(jiǎn)單文本。
        UILabel *label = [UILabel new];
        label.text = text;
        label.numberOfLines = rand() % 100;
        label.textAlignment = rand() % 5;
        label.lineBreakMode = rand() % 7;
        label.font = [UIFont systemFontOfSize:rand()%30 + 5.0];
       
        CFTimeInterval start = CACurrentMediaTime();
        CGSize sz1 = [label sizeThatFits:fitSize];
        simpleTextUILabelInterval += CACurrentMediaTime() - start;
        start = CACurrentMediaTime();
        CGSize sz2 = calcTextSize(fitSize, label.text, label.numberOfLines, label.font, label.textAlignment, label.lineBreakMode, label.minimumScaleFactor, CGSizeZero);
        simpleTextNOUILabelInterval += CACurrentMediaTime() - start;
        NSAssert(CGSizeEqualToSize(sz1, sz2), @"");
        
        //測(cè)試富文本
        NSRange range1 = NSMakeRange(0, rand()%text.length);
        NSMutableParagraphStyle *paragraphStyle1 = [[NSMutableParagraphStyle alloc] init];
        paragraphStyle1.lineSpacing = rand() % 20;
        paragraphStyle1.firstLineHeadIndent = rand() %10;
        paragraphStyle1.paragraphSpacing = rand() % 30;
        paragraphStyle1.headIndent = rand() % 10;
        paragraphStyle1.tailIndent = rand() % 10;
        UIFont *font1 = [UIFont systemFontOfSize:rand() % 20 + 3.0];
        
        NSRange range2 = NSMakeRange(range1.length, text.length - range1.length);
        NSMutableParagraphStyle *paragraphStyle2 = [[NSMutableParagraphStyle alloc] init];
        paragraphStyle2.lineSpacing = rand() % 20;
        paragraphStyle2.firstLineHeadIndent = rand() %10;
        paragraphStyle2.paragraphSpacing = rand() % 30;
        paragraphStyle2.headIndent = rand() % 10;
        paragraphStyle2.tailIndent = rand() % 10;
        UIFont *font2 = [UIFont systemFontOfSize:rand() % 20 + 3.0];
        
        NSMutableAttributedString *attributedText = [[NSMutableAttributedString alloc] initWithString:text];
        [attributedText addAttributes:@{NSParagraphStyleAttributeName:paragraphStyle1,NSFontAttributeName:font1} range:range1];
        [attributedText addAttributes:@{NSParagraphStyleAttributeName:paragraphStyle2,NSFontAttributeName:font2} range:range2];

        label = [UILabel new];
        label.numberOfLines = rand() % 100;
        label.textAlignment = rand() % 5;
        label.lineBreakMode = rand() % 7;
        label.font = [UIFont systemFontOfSize:rand()%30 + 5.0];
        label.attributedText = attributedText;
        
        start = CACurrentMediaTime();
        CGSize sz3 = [label sizeThatFits:fitSize];
        attributedTextUILabelInterval += CACurrentMediaTime() - start;
        start = CACurrentMediaTime();
        CGSize sz4 = calcTextSize(fitSize, label.attributedText, label.numberOfLines, label.font, label.textAlignment, label.lineBreakMode, 0.0, CGSizeZero);
        attributedTextNOUILabelInterval += CACurrentMediaTime() - start;
        NSAssert(CGSizeEqualToSize(sz3, sz4), @"");
    }
    
    simpleTextUILabelInterval *= 1000;
    simpleTextNOUILabelInterval *= 1000;
    attributedTextUILabelInterval *= 1000;
    attributedTextNOUILabelInterval *= 1000;
    NSLog(@"簡(jiǎn)單文本計(jì)算UILabel總耗時(shí)(毫秒):%.3f, 平均耗時(shí):%.3f",simpleTextUILabelInterval, simpleTextUILabelInterval / 5000);
    NSLog(@"簡(jiǎn)單文本計(jì)算非UILabel總耗時(shí)(毫秒):%.3f, 平均耗時(shí):%.3f",simpleTextNOUILabelInterval, simpleTextNOUILabelInterval / 5000);
    NSLog(@"富文本計(jì)算UILabel總耗時(shí)(毫秒):%.3f, 平均耗時(shí):%.3f",attributedTextUILabelInterval, attributedTextUILabelInterval / 5000);
    NSLog(@"富文本計(jì)算非UILabel總耗時(shí)(毫秒):%.3f, 平均耗時(shí):%.3f",attributedTextNOUILabelInterval, attributedTextNOUILabelInterval / 5000);
        

關(guān)注: 歐陽(yáng)大哥2013簡(jiǎn)書(shū)|歐陽(yáng)大哥2013掘金|歐陽(yáng)大哥2013Github