• 基于 CoreText 实现的高性能 UITableView

    1、绘制文本

    使用core text可以将文本绘制在一个CGContextRef上，最后再通过UIGraphicsGetImageFromCurrentImageContext()生成图片，再将图片赋值给cell.contentView.layer，从而达到减少cell层级的目的。

    绘制普通文本（譬如用户昵称）在context上，相关注释在代码里：

    [Objective-C] 查看源文件 复制代码
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    - (void)drawInContext:(CGContextRef)context withPosition:(CGPoint)p andFont:(UIFont *)font andTextColor:(UIColor *)color andHeight:(float)height andWidth:(float)width lineBreakMode:(CTLineBreakMode)lineBreakMode {
        CGSize size = CGSizeMake(width, height);
        // 翻转坐标系
        CGContextSetTextMatrix(context,CGAffineTransformIdentity);
        CGContextTranslateCTM(context,0,height);
        CGContextScaleCTM(context,1.0,-1.0);
     
        NSMutableDictionary* attributes = [StringAttributes attributeFont:font andTextColor:color lineBreakMode:lineBreakMode];
     
        // 创建绘制区域（路径）
        CGMutablePathRef path = CGPathCreateMutable();
        CGPathAddRect(path,NULL,CGRectMake(p.x, height-p.y-size.height,(size.width),(size.height)));
     
        // 创建AttributedString
        NSMutableAttributedString*attributedStr = [[NSMutableAttributedStringalloc] initWithString:selfattributes:attributes];
        CFAttributedStringRef attributedString = (__bridge CFAttributedStringRef)attributedStr;
     
        // 绘制frame
        CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attributedString);
        CTFrameRef ctframe = CTFramesetterCreateFrame(framesetter, CFRangeMake(0,0),path,NULL);
        CTFrameDraw(ctframe,context);
        CGPathRelease(path);
        CFRelease(framesetter);
        CFRelease(ctframe);
        [[attributedStr mutableString] setString:@""];
        CGContextSetTextMatrix(context,CGAffineTransformIdentity);
        CGContextTranslateCTM(context,0, height);
        CGContextScaleCTM(context,1.0,-1.0);
    }




    绘制朋友圈内容文本（带链接）在context上，这里我还没有去实现文本多了会折叠的效果，与上面普通文本不同的是这里需要创建带链接的AttributeString和CTLineRef的逐行绘制：

    [Objective-C] 查看源文件 复制代码
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    - (NSMutableAttributedString*)highlightText:(NSMutableAttributedString*)coloredString{
        // 创建带高亮的AttributedString
        NSString* string = coloredString.string;
        NSRangerange = NSMakeRange(0,[string length]);
        NSDataDetector*linkDetector = [NSDataDetectordataDetectorWithTypes:NSTextCheckingTypeLinkerror:nil];
        NSArray*matches = [linkDetector matchesInString:string options:0 range:range];
      
        for(NSTextCheckingResult* match in matches) {
            [self.ranges addObject:NSStringFromRange(match.range)];
            UIColor *highlightColor = UIColorFromRGB(0x297bc1);
            [coloredString addAttribute:(NSString*)kCTForegroundColorAttributeName
                                  value:(id)highlightColor.CGColor range:match.range];
        }
      
        returncoloredString;
    }
      
    - (void)drawFramesetter:(CTFramesetterRef)framesetter
           attributedString:(NSAttributedString*)attributedString
                  textRange:(CFRange)textRange
                     inRect:(CGRect)rect
                    context:(CGContextRef)c {
        CGMutablePathRef path = CGPathCreateMutable();
        CGPathAddRect(path,NULL, rect);
        CTFrameRef frame = CTFramesetterCreateFrame(framesetter, textRange, path, NULL);
      
        CGFloat ContentHeight = CGRectGetHeight(rect);
        CFArrayRef lines = CTFrameGetLines(frame);
        NSIntegernumberOfLines = CFArrayGetCount(lines);
      
        CGPoint lineOrigins[numberOfLines];
        CTFrameGetLineOrigins(frame, CFRangeMake(0, numberOfLines), lineOrigins);
      
        // 遍历每一行
        for(CFIndex lineIndex = 0; lineIndex < numberOfLines; lineIndex++) {
            CGPoint lineOrigin = lineOrigins[lineIndex];
            CTLineRef line = CFArrayGetValueAtIndex(lines, lineIndex);
      
            CGFloat descent = 0.0f, ascent = 0.0f, lineLeading = 0.0f;
            CTLineGetTypographicBounds((CTLineRef)line, &ascent, &descent, &lineLeading);
      
            CGFloat penOffset = (CGFloat)CTLineGetPenOffsetForFlush(line, NSTextAlignmentLeft, rect.size.width);
            CGFloat y = lineOrigin.y - descent - self.font.descender;
      
            // 设置每一行位置
            CGContextSetTextPosition(c, penOffset + self.xOffset, y - self.yOffset);
            CTLineDraw(line, c);
      
            // CTRunRef同一行中文本的不同样式，包括颜色、字体等，此处用途为处理链接高亮
            CFArrayRef runs = CTLineGetGlyphRuns(line);
            for(intj = 0; j < CFArrayGetCount(runs); j++) {
                CGFloat runAscent, runDescent, lineLeading1;
      
                CTRunRef run = CFArrayGetValueAtIndex(runs, j);
                NSDictionary*attributes = (__bridge NSDictionary*)CTRunGetAttributes(run);
                // 判断是不是链接
                if(!CGColorEqualToColor((__bridge CGColorRef)([attributes valueForKey:@"CTForegroundColor"]),self.textColor.CGColor)) {
                    CFRange range = CTRunGetStringRange(run);
                    floatoffset = CTLineGetOffsetForStringIndex(line, range.location, NULL);
      
                    // 得到链接的CGRect
                    CGRect runRect;
                    runRect.size.width = CTRunGetTypographicBounds(run, CFRangeMake(0,0), &runAscent, &runDescent, &lineLeading1);
                    runRect.size.height = self.font.lineHeight;
                    runRect.origin.x = lineOrigin.x + offset+ self.xOffset;
                    runRect.origin.y = lineOrigin.y;
                    runRect.origin.y -= descent + self.yOffset;
      
                    // 因为坐标系被翻转，链接正常的坐标需要通过CGAffineTransform计算得到
                    CGAffineTransform transform = CGAffineTransformMakeTranslation(0, ContentHeight);
                    transform = CGAffineTransformScale(transform, 1.f, -1.f);
                    CGRect flipRect = CGRectApplyAffineTransform(runRect, transform);
      
                    // 保存是链接的CGRect
                    NSRangenRange = NSMakeRange(range.location, range.length);
                    self.framesDict[NSStringFromRange(nRange)] = [NSValuevalueWithCGRect:flipRect];
      
                    // 保存同一条链接的不同CGRect，用于点击时背景色处理
                    for(NSString*rangeString in self.ranges) {
                        NSRangerange = NSRangeFromString(rangeString);
                        if(NSLocationInRange(nRange.location, range)) {
                            NSMutableArray*array = self.relationDict[rangeString];
                            if(array) {
                                [array addObject:NSStringFromCGRect(flipRect)];
                                self.relationDict[rangeString] = array;
                            }else{
                                self.relationDict[rangeString] = [NSMutableArrayarrayWithObject:NSStringFromCGRect(flipRect)];
                            }
                        }
                    }
      
                }
            }
        }
      
        CFRelease(frame);
        CFRelease(path);
    }






    上述方法运用起来就是：

    [Objective-C] 查看源文件 复制代码
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    - (void)fillData:(CGContextRef)context {
        [self.nickname drawInContext:context withPosition:(CGPoint){kTextXOffset, kSpec} andFont:kNicknameFont
                        andTextColor:UIColorFromRGB(0x556c95) andHeight:self.nicknameSize.height
                            andWidth:self.nicknameSize.width lineBreakMode:kCTLineBreakByTruncatingTail];
        [self.drawer setText:self.contentString context:context contentSize:self.contentSize
             backgroundColor:[UIColor whiteColor] font:kContentTextFont textColor:[UIColor blackColor]
                       block:nilxOffset:kTextXOffset yOffset:kSpec * 2 + self.nicknameSize.height];
    }
      
    - (void)fillContents:(NSArray*)array {
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(self.size.width,self.size.height),YES, 0);
        CGContextRef context = UIGraphicsGetCurrentContext();
        [UIColorFromRGB(0xffffff) set];
        CGContextFillRect(context, CGRectMake(0, 0, self.size.width,self.size.height));
      
        // 获取需要高亮的链接CGRect，并填充背景色
        if(array) {
            for(NSString*string in array) {
                CGRect rect = CGRectFromString(string);
                [UIColorFromRGB(0xe5e5e5) set];
                CGContextFillRect(context, rect);
            }
        }
      
        [selffillData:context];
      
        UIImage *temp = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        self.contentView.layer.contents = (__bridge id_Nullable)(temp.CGImage);
    }




    这样就完成了文本的显示。

    2、显示图片

    图片包括用户头像和朋友圈的内容，这里只是将CALayer添加到contentView.layer上，具体做法是继承了CALayer，实现部分功能。

    通过链接显示图片：

    [Objective-C] 查看源文件 复制代码
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    - (void)setContentsWithURLString:(NSString*)urlString {
      
        self.contents = (__bridge id_Nullable)([UIImage imageNamed:@"placeholder"].CGImage);
        @weakify(self)
        SDWebImageManager *manager = [SDWebImageManager sharedManager];
        [manager downloadImageWithURL:[NSURLURLWithString:urlString]
                              options:SDWebImageCacheMemoryOnly
                             progress:nil
                            completed:^(UIImage *image, NSError*error, SDImageCacheType cacheType, BOOLfinished, NSURL*imageURL) {
                                if(image) {
                                    @strongify(self)
                                    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                                        if(!_observer) {
      
                                            _observer = CFRunLoopObserverCreateWithHandler(kCFAllocatorDefault, kCFRunLoopBeforeWaiting | kCFRunLoopExit,false, POPAnimationApplyRunLoopOrder, ^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) {
                                                self.contents = (__bridge id_Nullable)(image.CGImage);
                                            });
      
                                            if(_observer) {
                                                CFRunLoopAddObserver(CFRunLoopGetMain(), _observer,  kCFRunLoopCommonModes);
                                            }
                                        }
                                    });
                                    self.originImage = image;
                                }
                            }];
    }




    3、显示小视频

    之前的一篇文章简单讲了怎么自己做一个播放器，这里就派上用场了。而显示小视频封面图片的CALayer同样在显示小视频的时候可以复用。

    这里使用了NSOperationQueue来保障播放视频的流畅性，具体继承NSOperation的VideoDecodeOperation相关代码如下：

    [Objective-C] 查看源文件 复制代码
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    - (void)main {
      
        @autoreleasepool{
      
            if(self.isCancelled) {
                _newVideoFrameBlock = nil;
                _decodeFinishedBlock = nil;
                return;
            }
      
            AVURLAsset *asset = [AVURLAsset URLAssetWithURL:[[NSURLalloc] initFileURLWithPath:self.filePath] options:nil];
            NSError*error;
            AVAssetReader* reader = [[AVAssetReader alloc] initWithAsset:asset error:&error];
            if(error) {
                return;
            }
      
            NSArray* videoTracks = [asset tracksWithMediaType:AVMediaTypeVideo];
            AVAssetTrack* videoTrack = [videoTracks objectAtIndex:0];
            // 视频播放时，m_pixelFormatType=kCVPixelFormatType_32BGRA
            // 其他用途，如视频压缩，m_pixelFormatType=kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange
            intm_pixelFormatType = kCVPixelFormatType_32BGRA;
            NSDictionary* options = [NSDictionarydictionaryWithObject:[NSNumbernumberWithInt: (int)m_pixelFormatType]
                                                                forKey:(id)kCVPixelBufferPixelFormatTypeKey];
            AVAssetReaderTrackOutput* videoReaderOutput = [[AVAssetReaderTrackOutput alloc]
                    initWithTrack:videoTrack outputSettings:options];
            [reader addOutput:videoReaderOutput];
            [reader startReading];
            // 要确保nominalFrameRate>0，之前出现过android拍的0帧视频
            if(self.isCancelled) {
                _newVideoFrameBlock = nil;
                _decodeFinishedBlock = nil;
                return;
            }
      
            while([reader status] == AVAssetReaderStatusReading && videoTrack.nominalFrameRate > 0) {
                if(self.isCancelled) {
                    _newVideoFrameBlock = nil;
                    _decodeFinishedBlock = nil;
                    return;
                }
      
                CMSampleBufferRef sampleBuffer = [videoReaderOutput copyNextSampleBuffer];
                CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
      
                // Lock the base address of the pixel buffer
                CVPixelBufferLockBaseAddress(imageBuffer, 0);
      
                // Get the number of bytes per row for the pixel buffer
                size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
      
                // Get the pixel buffer width and height
                size_t width = CVPixelBufferGetWidth(imageBuffer);
                size_t height = CVPixelBufferGetHeight(imageBuffer);
      
                //Generate image to edit`
                unsignedchar* pixel = (unsigned char*)CVPixelBufferGetBaseAddress(imageBuffer);
      
                CGColorSpaceRef colorSpace=CGColorSpaceCreateDeviceRGB();
                CGContextRef context=CGBitmapContextCreate(pixel, width, height, 8, bytesPerRow, colorSpace,
                                                           kCGBitmapByteOrder32Little|kCGImageAlphaPremultipliedFirst);
                if(context != NULL) {
                    CGImageRef imageRef = CGBitmapContextCreateImage(context);
      
                    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
                    CGColorSpaceRelease(colorSpace);
                    CGContextRelease(context);
      
                    // 解码图片
                    size_t width = CGImageGetWidth(imageRef);
                    size_t height = CGImageGetHeight(imageRef);
                    size_t bitsPerComponent = CGImageGetBitsPerComponent(imageRef);
      
                    // CGImageGetBytesPerRow() calculates incorrectly in iOS 5.0, so defer to CGBitmapContextCreate
                    size_t bytesPerRow = 0;
                    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
                    CGColorSpaceModel colorSpaceModel = CGColorSpaceGetModel(colorSpace);
                    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
      
                    if(colorSpaceModel == kCGColorSpaceModelRGB) {
                        uint32_t alpha = (bitmapInfo & kCGBitmapAlphaInfoMask);
    #pragma clang diagnostic push
    #pragma clang diagnostic ignored "-Wassign-enum"
                        if(alpha == kCGImageAlphaNone) {
                            bitmapInfo &= ~kCGBitmapAlphaInfoMask;
                            bitmapInfo |= kCGImageAlphaNoneSkipFirst;
                        }elseif (!(alpha == kCGImageAlphaNoneSkipFirst || alpha == kCGImageAlphaNoneSkipLast)) {
                            bitmapInfo &= ~kCGBitmapAlphaInfoMask;
                            bitmapInfo |= kCGImageAlphaPremultipliedFirst;
                        }
    #pragma clang diagnostic pop
                    }
      
                    CGContextRef context = CGBitmapContextCreate(NULL, width, height, bitsPerComponent,
                                                                 bytesPerRow, colorSpace, bitmapInfo);
      
                    CGColorSpaceRelease(colorSpace);
      
                    if(!context) {
                        if(self.newVideoFrameBlock) {
                            dispatch_async(dispatch_get_main_queue(), ^{
                                if(self.isCancelled) {
                                    _newVideoFrameBlock = nil;
                                    _decodeFinishedBlock = nil;
                                    return;
                                }
                                self.newVideoFrameBlock(imageRef,self.filePath);
                                CGImageRelease(imageRef);
                            });
                        }
                    }else{
      
                        CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, width, height), imageRef);
                        CGImageRef inflatedImageRef = CGBitmapContextCreateImage(context);
      
                        CGContextRelease(context);
                        if(self.newVideoFrameBlock) {
                            dispatch_async(dispatch_get_main_queue(), ^{
                                if(self.isCancelled) {
                                    _newVideoFrameBlock = nil;
                                    _decodeFinishedBlock = nil;
                                    return;
                                }
                                self.newVideoFrameBlock(inflatedImageRef,self.filePath);
      
                                CGImageRelease(inflatedImageRef);
                            });
                        }
                        CGImageRelease(imageRef);
                    }
      
                    if(sampleBuffer) {
                        CMSampleBufferInvalidate(sampleBuffer);
                        CFRelease(sampleBuffer);
                        sampleBuffer = NULL;
      
                    }else{
                        break;
                    }
                }
      
                [NSThreadsleepForTimeInterval:CMTimeGetSeconds(videoTrack.minFrameDuration)];
            }
      
            if(self.isCancelled) {
                _newVideoFrameBlock = nil;
                _decodeFinishedBlock = nil;
                return;
            }
            if(self.decodeFinishedBlock) {
                self.decodeFinishedBlock(self.filePath);
            }
        }
    }




    解码图片是因为UIImage在界面需要显示的时候才开始解码，这样可能会造成主线程的卡顿，所以在子线程对其进行解压缩处理。

    具体的使用：

    [Objective-C] 查看源文件 复制代码
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    - (void)playVideoWithFilePath:(NSString*)filePath_ type:(NSString*)type {
        @weakify(self)
        [[VideoPlayerManager shareInstance] decodeVideo:filePath_
                                  withVideoPerDataBlock:^(CGImageRef imageData, NSString*filePath) {
                                      @strongify(self)
                                      if([type isEqualToString:@"video"]) {
                                          if([filePath isEqualToString:self.filePath]) {
                                              [self.sources.firstObject
                                                      setContents:(__bridgeid_Nullable)(imageData)];
                                          }
                                      }
                                  } decodeFinishBlock:^(NSString*filePath){
                    [selfplayVideoWithFilePath:filePath type:type];
                }];
    }
     
     


    4、其他

    1、触摸交互是覆盖了以下方法实现：

    [Objective-C] 查看源文件 复制代码
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    <font style="color:rgb(46, 46, 46)"><font face="&quot;"><font style="font-size:15px">- (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
    - (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
    - (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
    </font></font></font>










    2、页面上FPS的测量是使用了YYKit项目中的YYFPSLabel。

    DEMO 下载：
    http://www.code4app.com/forum.php?mod=viewthread&tid=9469&extra=page%3D1%26filter%3Dsortid%26sortid%3D1
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  • 原文地址：https://www.cnblogs.com/kengsir/p/5670075.html
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