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YYText

YYText 是YYKit中的一个富文本显示,编辑组件,拥有YYLabel,YYTextView 两个控件。其中YYLabel类似于UILabel,但功能更为强大,支持异步文本渲染,更丰富的效果显示,支持UIImage,UIView, CALayer 文本附件,自定义强调文本范围,支持垂直文本显示等等。YYTextView 类似UITextView,除了兼容UITextView API,扩展了更多的CoreText 效果属性,支持高亮链接,支持自定义内部文本路径形状,支持图片拷贝,粘贴等等。

下面是YYText 与 TextKit 的比较图:

YYText

YYLabel

YYLabel 的实现,是基于 CoreText 框架 在 Context 上进行绘制,通过设置 NSMutableAttributedString 实现文本各种效果属性的展现。下面是YYLabel 主要相关的部分:

  • YYAsyncLayer: YYLabel的异步渲染,通过YYAsyncLayerDisplayTask 回调渲染
  • YYTextLayout: YYLabel的布局管理类,也负责绘制
  • YYTextContainer: YYLabel的布局类
  • NSAttributedString+YYText: YYLabel 所有效果属性设置

YYAsyncLayer 的异步实现

YYAsyncLayer 是 CALayer的子类,通过设置 YYLabel 类方法 layerClass
返回自定义的 YYAsyncLayer ,重写了父类的 setNeedsDisplay , display 实现 contents 自定义刷新。 YYAsyncLayerDelegate 返回新的刷新任务 newAsyncDisplayTask 用于更新过程回调,返回到 YYLabel 进行文本渲染。其中 YYSentinel 是一个线程安全的原子递增计数器,用于判断更新是否取消。

YYTextLayout

YYLabel 实现了 YYAsyncLayerDelegate 代理方法 newAsyncDisplayTask ,回调处理3种文本渲染状态willDisplay ,display,didDisplay 。在渲染之前,移除不需要的文本附件,渲染完成后,添加需要的文本附件。渲染时,首先获取 YYTextLayout , 一般包含了 YYTextContainerNSAttributedString 两部分, 分别负责文本展示的形状和内容。不管是渲染时和渲染完成后,最后都需要调用 YYTextLayout

- (void) drawInContext:(CGContextRef)context
                 size:(CGSize)size
                point:(CGPoint)point
                 view:(UIView *)view
                layer:(CALayer *)layer
                debug:(YYTextDebugOption *)debug
                cancel:(BOOL (^)(void))cancel{

其中 context 是图形上下文,文本的绘制在它上面进行, size 是 context 的大小, point 是绘制的起始点, view , layer 是添加文本附件的视图(层), debug 调试选项, cancel 取消绘制,根据传入的文本是否需要绘制YYText自定义属性效果依次进行相应的绘制。有以下这些属性:

///< Has highlight attribute
@property (nonatomic, readonly) BOOL containsHighlight;
///< Has block border attribute
@property (nonatomic, readonly) BOOL needDrawBlockBorder;
///< Has background border attribute
@property (nonatomic, readonly) BOOL needDrawBackgroundBorder;
///< Has shadow attribute
@property (nonatomic, readonly) BOOL needDrawShadow;
///< Has underline attribute
@property (nonatomic, readonly) BOOL needDrawUnderline;
///< Has visible text
@property (nonatomic, readonly) BOOL needDrawText;
///< Has attachment attribute
@property (nonatomic, readonly) BOOL needDrawAttachment;
///< Has inner shadow attribute
@property (nonatomic, readonly) BOOL needDrawInnerShadow;
///< Has strickthrough attribute
@property (nonatomic, readonly) BOOL needDrawStrikethrough;
///< Has border attribute
@property (nonatomic, readonly) BOOL needDrawBorder;

以其中的 needDrawShadow 为例,在Demo中 YYTextAttributeExample.m , 为文本 Shadow 自定义了 textShadow , 在 NSAttributedString+YYText.m 中 调用 addAttribute:(NSString *)name value:(id)value range:(NSRange)range 添加了此文本属性。可以在 YYTextAttribute 查看所有属性信息

最后在 YYTextLayout 的初始化方法中获取,代码如下:

layout.needDrawText = YES;
   void (^block)(NSDictionary *attrs, NSRange range, BOOL *stop) = ^(NSDictionary *attrs, NSRange range, BOOL *stop) {
       if (attrs[YYTextHighlightAttributeName]) layout.containsHighlight = YES;
       if (attrs[YYTextBlockBorderAttributeName]) layout.needDrawBlockBorder = YES;
       if (attrs[YYTextBackgroundBorderAttributeName]) layout.needDrawBackgroundBorder = YES;
       if (attrs[YYTextShadowAttributeName] || attrs[NSShadowAttributeName]) layout.needDrawShadow = YES;
       if (attrs[YYTextUnderlineAttributeName]) layout.needDrawUnderline = YES;
       if (attrs[YYTextAttachmentAttributeName]) layout.needDrawAttachment = YES;
       if (attrs[YYTextInnerShadowAttributeName]) layout.needDrawInnerShadow = YES;
       if (attrs[YYTextStrikethroughAttributeName]) layout.needDrawStrikethrough = YES;
       if (attrs[YYTextBorderAttributeName]) layout.needDrawBorder = YES;
   };
   
   [layout.text enumerateAttributesInRange:visibleRange options:NSAttributedStringEnumerationLongestEffectiveRangeNotRequired usingBlock:block];

根据 YYTextContainerNSAttributedString 生成 YYTextLayout ,接下来就是渲染了, 具体的渲染由 CoreText 来实现。

CoreText

CoreText 是iOS/OSX里的文字渲染引擎,在iOS/OSX上看到的所有文字在底层都是由CoreText去渲染。

YYText

一个 NSAttributeString 通过CoreText的 CTFramesetterCreateWithAttributedString 生成 CTFramesetter ,它是创建 CTFrame 的工厂,为 CTFramesetter 提供一个 CGPath ,它就会通过它持有的 CTTypesetter 生成 CTFrameCTFrame 里面包含了 CTLine CTLine 中包含了此行所有的 CTRun ,然后就可以绘制到画布上。 CTFrame , CTLine , CTRun 都提供了渲染接口,但前两者是封装,最后实际都是调用到 CTRun 的渲染接口去绘制。

在YYTextlayout 中的代码体现

// create CoreText objects
  ctSetter = CTFramesetterCreateWithAttributedString((CFTypeRef)text);
  if (!ctSetter) goto fail;
  ctFrame = CTFramesetterCreateFrame(ctSetter, YYCFRangeFromNSRange(range), cgPath, (CFTypeRef)frameAttrs);
  if (!ctFrame) goto fail;
  lines = [NSMutableArray new];
  ctLines = CTFrameGetLines(ctFrame);
  lineCount = CFArrayGetCount(ctLines);
  if (lineCount > 0) {
      lineOrigins = malloc(lineCount * sizeof(CGPoint));
      if (lineOrigins == NULL) goto fail;
      CTFrameGetLineOrigins(ctFrame, CFRangeMake(0, lineCount), lineOrigins);
  }
  
  CGRect textBoundingRect = CGRectZero;
  CGSize textBoundingSize = CGSizeZero;
  NSInteger rowIdx = -1;
  NSUInteger rowCount = 0;
  CGRect lastRect = CGRectMake(0, -FLT_MAX, 0, 0);
  CGPoint lastPosition = CGPointMake(0, -FLT_MAX);
  if (isVerticalForm) {
      lastRect = CGRectMake(FLT_MAX, 0, 0, 0);
      lastPosition = CGPointMake(FLT_MAX, 0);
  }

在这之前,需要生成 CGPath 根据 YYTextContainer 生成

// set cgPath and cgPathBox
   if (container.path == nil && container.exclusionPaths.count == 0) {
       if (container.size.width <= 0 || container.size.height <= 0) goto fail;
       CGRect rect = (CGRect) {CGPointZero, container.size };
       if (needFixLayoutSizeBug) {
           constraintSizeIsExtended = YES;
           constraintRectBeforeExtended = UIEdgeInsetsInsetRect(rect, container.insets);
           constraintRectBeforeExtended = CGRectStandardize(constraintRectBeforeExtended);
           if (container.isVerticalForm) {
               rect.size.width = YYTextContainerMaxSize.width;
           } else {
               rect.size.height = YYTextContainerMaxSize.height;
           }
       }
       rect = UIEdgeInsetsInsetRect(rect, container.insets);
       rect = CGRectStandardize(rect);
       cgPathBox = rect;
       rect = CGRectApplyAffineTransform(rect, CGAffineTransformMakeScale(1, -1));
       cgPath = CGPathCreateWithRect(rect, NULL); // let CGPathIsRect() returns true
   } else if (container.path && CGPathIsRect(container.path.CGPath, &cgPathBox) && container.exclusionPaths.count == 0) {
       CGRect rect = CGRectApplyAffineTransform(cgPathBox, CGAffineTransformMakeScale(1, -1));
       cgPath = CGPathCreateWithRect(rect, NULL); // let CGPathIsRect() returns true
   } else {
       rowMaySeparated = YES;
       CGMutablePathRef path = NULL;
       if (container.path) {
           path = CGPathCreateMutableCopy(container.path.CGPath);
       } else {
           CGRect rect = (CGRect) {CGPointZero, container.size };
           rect = UIEdgeInsetsInsetRect(rect, container.insets);
           CGPathRef rectPath = CGPathCreateWithRect(rect, NULL);
           if (rectPath) {
               path = CGPathCreateMutableCopy(rectPath);
               CGPathRelease(rectPath);
           }
       }
       if (path) {
           [layout.container.exclusionPaths enumerateObjectsUsingBlock: ^(UIBezierPath *onePath, NSUInteger idx, BOOL *stop) {
               CGPathAddPath(path, NULL, onePath.CGPath);
           }];
           
           cgPathBox = CGPathGetPathBoundingBox(path);
           CGAffineTransform trans = CGAffineTransformMakeScale(1, -1);
           CGMutablePathRef transPath = CGPathCreateMutableCopyByTransformingPath(path, &trans);
           CGPathRelease(path);
           path = transPath;
       }
       cgPath = path;
   }

YYTextContainer 有下面两个属性,可以用来自定义path

/// Custom constrained path. Set this property to ignore `size` and `insets`. Default is nil.
@property (nullable, copy) UIBezierPath *path;

/// An array of `UIBezierPath` for path exclusion. Default is nil.
@property (nullable, copy) NSArray<UIBezierPath *> *exclusionPaths;

复杂的就是每行的frame的计算, calculate line frame 部分,看的有点晕~~~

需要进行坐标系的转化, YYTextLine 是对 CTLine 的进一步封装。

YYText

最终文字的绘制都会调用

YYTextDrawText(YYTextLayout *layout, CGContextRef context, CGSize size, CGPoint point, BOOL (^cancel)(void))
//坐标系变化
CGContextTranslateCTM(context, point.x, point.y);
CGContextTranslateCTM(context, 0, size.height);
CGContextScaleCTM(context, 1, -1);
CGContextSaveGState(context); {  
 // 所有的渲染有关代码    
} CGContextRestoreGState(context);

最后都需要调用 YYTextDrawRun 进行绘制 CTRunDraw(run, context, CFRangeMake(0, 0));

YYTextView

其绘制原理同 YYLabel,其中 YYTextContainerView 是文本显示的视图,其 layout 属性用来绘制文本。

原文  http://ChenAo0727.github.io/2017/01/22/YYText/
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