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基于 CoreText 实现的高性能 UITableView-ios学习从入门到精通尽在姬长信

姬長信姬長信 日记 2016-07-15
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引起UITableView卡顿对照常见的原因有cell的层级过多、cell中有触发离屏渲染的代码（譬如：cornerRadius、maskToBounds 同时使用）、像素是否对齐、是否使用UITableView自动计算cell高度的要领等。本文将从cell层级出发，以一个仿朋友圈的demo来讲述如何让列表保持顺滑，项目的源码可在文末获得。不可否认的是，过早的优化是魔鬼，请在项目出现性能瓶颈再考虑优化。

首先看看reveal上页面层级的效果图

2b08a274-46aa-11e6-9936-79cbdcaf3869.png

然后是9.3系统iPhone5的真机效果

506d7242-46b4-11e6-9bad-6b4a5d05c0a5.gif

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，从而到达减少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：

- (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 = [[NSMutableAttributedString alloc] initWithString:self attributes: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，与上面普通文本差别的是这里需要创建带链接的AttributeString和CTLineRef的逐行绘制：

- (NSMutableAttributedString *)highlightText:(NSMutableAttributedString *)coloredString{
    // 创建带高亮的AttributedString
    NSString* string = coloredString.string;
    NSRange range = NSMakeRange(0,[string length]);
    NSDataDetector *linkDetector = [NSDataDetector dataDetectorWithTypes:NSTextCheckingTypeLink error: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];
    }
    return coloredString;
}
- (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);
    NSInteger numberOfLines = 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 (int j = 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);
                float offset = 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
                NSRange nRange = NSMakeRange(range.location, range.length);
                self.framesDict[NSStringFromRange(nRange)] = [NSValue valueWithCGRect: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) {
                    NSRange range = 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] = [NSMutableArray arrayWithObject:NSStringFromCGRect(flipRect)];
                        }
                    }
                }
            }
        }
    }
    CFRelease(frame);
    CFRelease(path);
}

上述要领运用起来就是：

- (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:nil xOffset: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，并填充配景色
    if (array) {
        for (NSString *string in array) {
            CGRect rect = CGRectFromString(string);
            [UIColorFromRGB(0xe5e5e5) set];
            CGContextFillRect(context, rect);
        }
    }
    [self fillData: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

图片包罗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，实现部门功能。

通过链接显示图片：

- (void)setContentsWithURLString:(NSString *)urlString {
    self.contents = (__bridge id _Nullable)([UIImage imageNamed:@"placeholder"].CGImage);
    @weakify(self)
    SDWebImageManager *manager = [SDWebImageManager sharedManager];
    [manager downloadImageWithURL:[NSURL URLWithString:urlString]
                          options:SDWebImageCacheMemoryOnly
                         progress:nil
                        completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, 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;
                            }
                        }];
}

其他对照简单就不展开。

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：

- (void)main {
    @autoreleasepool {
        if (self.isCancelled) {
            _newVideoFrameBlock = nil;
            _decodeFinishedBlock = nil;
            return;
        }
        AVURLAsset *asset = [AVURLAsset URLAssetWithURL:[[NSURL alloc] 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
        int m_pixelFormatType = kCVPixelFormatType_32BGRA;
        NSDictionary* options = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt: (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`
            unsigned char* 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;
                    } else if (!(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;
                }
            }
            [NSThread sleepForTimeInterval: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：

- (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:(__bridge id _Nullable)(imageData)];
                                      }
                                  }
                              } decodeFinishBlock:^(NSString *filePath){
                [self playVideoWithFilePath:filePath type:type];
            }];
}

4、其他

1、触摸交互是覆笼罩了以下要领实现：

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event

2、页面上FPS的丈量是使用了YYKit项目中的YYFPSLabel。

3、测试数据是微博找的，其中小视频是Gif快手。

本文的代码在https://github.com/hawk0620/PYQFeedDemo

本文作者：伯乐在线 - Hawk0620

用意志战胜身体的惰性！

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本文由 姬長信 创作，文章地址：https://blog.isoyu.com/archives/726.html
采用知识共享署名4.0 国际许可协议进行许可。除注明转载/出处外，均为本站原创或翻译，转载前请务必署名。最后编辑时间为:7 月 15, 2016 at 07:43 上午

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