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iOS WKWebview 白屏检测实现
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前言
自ios8推出wkwebview以来，极大改善了网页加载速度及内存泄漏问题，逐渐全面取代笨重的UIWebview。尽管高性能、高刷新的WKWebview在混合开发中大放异彩表现优异，但加载网页过程中出现异常白屏的现象却仍然屡见不鲜，且现有的api协议处理捕捉不到这种异常case，造成用户无用等待体验很差。 针对业务场景需求，实现加载白屏检测。考虑采用字节跳动团队提出的webview优化技术方案。在合适的加载时机对当前webview可视区域截图，并对此快照进行像素点遍历，如果非白屏颜色的像素点超过一定的阈值，认定其为非白屏，反之重新加载请求。 获取快照ios官方提供了简易的获取webview快照接口，通过异步回调拿到当前可视区域的屏幕截图。 - (void)takeSnapshotWithConfiguration:(nullable WKSnapshotConfiguration *)snapshotConfiguration completionHandler:(void (^)(UIImage * _Nullable snapshotImage, NSError * _Nullable error))completionHandler API_AVAILABLE(ios(11.0)); 复制代码其中snapshotConfiguration 参数可用于配置快照大小范围，默认截取当前客户端整个屏幕区域。由于可能出现导航栏成功加载而内容页却空白的特殊情况，导致非白屏像素点数增加对最终判定结果造成影响，考虑将其剔除。 - (void)judgeLoadingStatus:(WKWebView *)webview { if (@available(iOS 11.0, *)) { if (webView && [webView isKindOfClass:[WKWebView class]]) { CGFloat statusBarHeight = [[UIApplication sharedApplication] statusBarFrame].size.height; //状态栏高度 CGFloat navigationHeight = webView.viewController.navigationController.navigationBar.frame.size.height; //导航栏高度 WKSnapshotConfiguration *shotConfiguration = [[WKSnapshotConfiguration alloc] init]; shotConfiguration.rect = CGRectMake(0, statusBarHeight + navigationHeight, _webView.bounds.size.width, (_webView.bounds.size.height - navigationHeight - statusBarHeight)); //仅截图检测导航栏以下部分内容 [_webView takeSnapshotWithConfiguration:shotConfiguration completionHandler:^(UIImage * _Nullable snapshotImage, NSError * _Nullable error) { //todo }]; } } } 复制代码 缩放快照为了提升检测性能，考虑将快照缩放至1/5，减少像素点总数，从而加快遍历速度。 - (UIImage *)scaleImage: (UIImage *)image { CGFloat scale = 0.2; CGSize newsize; newsize.width = floor(image.size.width * scale); newsize.height = floor(image.size.height * scale); if (@available(iOS 10.0, *)) { UIGraphicsImageRenderer * renderer = [[UIGraphicsImageRenderer alloc] initWithSize:newsize]; return [renderer imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) { [image drawInRect:CGRectMake(0, 0, newsize.width, newsize.height)]; }]; }else{ return image; } } 复制代码缩小前后性能对比（实验环境：iPhone11同一页面下）： 缩放前白屏检测： 耗时20ms 缩放后白屏检测： 耗时13ms 注意这里有个小坑。由于缩略图的尺寸在 原图宽高*缩放系数后可能不是整数，在布置画布重绘时默认向上取整，这就造成画布比实际缩略图大（混蛋啊 摔！）。在遍历缩略图像素时，会将图外画布上的像素纳入考虑范围，导致实际白屏页 像素占比并非100% 如图所示。因此使用floor将其尺寸大小向下取整。 遍历快照遍历快照缩略图像素点，对白色像素(R:255 G: 255 B: 255)占比大于95%的页面，认定其为白屏。 - (BOOL)searchEveryPixel:(UIImage *)image { CGImageRef cgImage = [image CGImage]; size_t width = CGImageGetWidth(cgImage); size_t height = CGImageGetHeight(cgImage); size_t bytesPerRow = CGImageGetBytesPerRow(cgImage); //每个像素点包含r g b a 四个字节 size_t bitsPerPixel = CGImageGetBitsPerPixel(cgImage); CGDataProviderRef dataProvider = CGImageGetDataProvider(cgImage); CFDataRef data = CGDataProviderCopyData(dataProvider); UInt8 * buffer = (UInt8*)CFDataGetBytePtr(data); int whiteCount = 0; int totalCount = 0; for (int j = 0; j < height; j ++ ) { for (int i = 0; i < width; i ++) { UInt8 * pt = buffer + j * bytesPerRow + i * (bitsPerPixel / 8); UInt8 red = * pt; UInt8 green = *(pt + 1); UInt8 blue = *(pt + 2); // UInt8 alpha = *(pt + 3); totalCount ++; if (red == 255 && green == 255 && blue == 255) { whiteCount ++; } } } float proportion = (float)whiteCount / totalCount ; NSLog(@"当前像素点数：%d,白色像素点数:%d , 占比: %f",totalCount , whiteCount , proportion ); if (proportion > 0.95) { return YES; }else{ return NO; } } 复制代码 总结 typedef NS_ENUM(NSUInteger,webviewLoadingStatus) { WebViewNormalStatus = 0, //正常 WebViewErrorStatus, //白屏 WebViewPendStatus, //待决 }; // 判断是否白屏 - (void)judgeLoadingStatus:(WKWebview *)webview withBlock:(void (^)(webviewLoadingStatus status))completionBlock{ webviewLoadingStatus __block status = WebViewPendStatus; if (@available(iOS 11.0, *)) { if (webview && [webview isKindOfClass:[WKWebView class]]) { CGFloat statusBarHeight = [[UIApplication sharedApplication] statusBarFrame].size.height; //状态栏高度 CGFloat navigationHeight = webview.viewController.navigationController.navigationBar.frame.size.height; //导航栏高度 WKSnapshotConfiguration *shotConfiguration = [[WKSnapshotConfiguration alloc] init]; shotConfiguration.rect = CGRectMake(0, statusBarHeight + navigationHeight, webview.bounds.size.width, (webview.bounds.size.height - navigationHeight - statusBarHeight)); //仅截图检测导航栏以下部分内容 [webview takeSnapshotWithConfiguration:shotConfiguration completionHandler:^(UIImage * _Nullable snapshotImage, NSError * _Nullable error) { if (snapshotImage) { CGImageRef imageRef = snapshotImage.CGImage; UIImage * scaleImage = [self scaleImage:snapshotImage]; BOOL isWhiteScreen = [self searchEveryPixel:scaleImage]; if (isWhiteScreen) { status = WebViewErrorStatus; }else{ status = WebViewNormalStatus; } } if (completionBlock) { completionBlock(status); } }]; } } } // 遍历像素点 白色像素占比大于95%认定为白屏 - (BOOL)searchEveryPixel:(UIImage *)image { CGImageRef cgImage = [image CGImage]; size_t width = CGImageGetWidth(cgImage); size_t height = CGImageGetHeight(cgImage); size_t bytesPerRow = CGImageGetBytesPerRow(cgImage); //每个像素点包含r g b a 四个字节 size_t bitsPerPixel = CGImageGetBitsPerPixel(cgImage); CGDataProviderRef dataProvider = CGImageGetDataProvider(cgImage); CFDataRef data = CGDataProviderCopyData(dataProvider); UInt8 * buffer = (UInt8*)CFDataGetBytePtr(data); int whiteCount = 0; int totalCount = 0; for (int j = 0; j < height; j ++ ) { for (int i = 0; i < width; i ++) { UInt8 * pt = buffer + j * bytesPerRow + i * (bitsPerPixel / 8); UInt8 red = * pt; UInt8 green = *(pt + 1); UInt8 blue = *(pt + 2); // UInt8 alpha = *(pt + 3); totalCount ++; if (red == 255 && green == 255 && blue == 255) { whiteCount ++; } } } float proportion = (float)whiteCount / totalCount ; NSLog(@"当前像素点数：%d,白色像素点数:%d , 占比: %f",totalCount , whiteCount , proportion ); if (proportion > 0.95) { return YES; }else{ return NO; } } //缩放图片 - (UIImage *)scaleImage: (UIImage *)image { CGFloat scale = 0.2; CGSize newsize; newsize.width = floor(image.size.width * scale); newsize.height = floor(image.size.height * scale); if (@available(iOS 10.0, *)) { UIGraphicsImageRenderer * renderer = [[UIGraphicsImageRenderer alloc] initWithSize:newsize]; return [renderer imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) { [image drawInRect:CGRectMake(0, 0, newsize.width, newsize.height)]; }]; }else{ return image; } } 复制代码仅需在合适的view生命周期内回调使用该函数方法即可检测出页面状态是否白屏，且性能损耗可忽略不计。 声明本文为作者原创，转载请注明出处。 |
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