WKWebView虽好，但白屏问题也很苦恼，下面分享一下自己解决问题的过程。

公司项目使用Cordova框架，做原生项目嵌入H5，业务复杂了以后，H5资源也越来越大，占用内存越来越多，加载也越来越慢，直到做热更新时候，遇到了白屏问题。

第一步：有说白屏时候回调webViewWebContentProcessDidTerminate方法，那就加上吧：

- (void)webViewWebContentProcessDidTerminate:(WKWebView *)webView {
    [webView reload];
}

然而没用，根本不回调。

第二步：-(void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigation {  }方法中加载外部JS导致白屏，那就去掉，然而还是没用。

第三步：由于做热更新，加载了本地H5资源，注意本地H5资源必须放到沙盒Documents目录下才能被WKWebView访问，放在tmp或Library下根本不行。

NSURL *url = [NSURL fileURLWithPath:urlString];
[webView loadRequest:[NSURLRequest requestWithURL:url]];

这样使用，还是不行。改成：

NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:30];
[webView loadRequest:request];

并且WKWebView初始化时候，加上允许访问FileURL：

 [configuration.preferences setValue:@YES forKey:@"allowFileAccessFromFileURLs"];
 [configuration setValue:@YES forKey:@"_allowUniversalAccessFromFileURLs"];

发现模拟器上不白屏了，但高兴太早了，真机测试，依然白屏。

第四步：参考字节分享的白屏重载方法

-(void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigation
{
    [self judgeLoadingStatus:webView withBlock:^(webviewLoadingStatus status) {
            switch (status) {
                case WebViewErrorStatus:
                    self.reloadTime += 1;
                    if (self.reloadTime > 2) {
                        return;
                    }
                    [webView reload];
                    NSLog(@"遇到白屏，重新加载🆘");
                    break;
                    
                default:
                    break;
            }
        }];
}

// 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) {
            // 状态栏高度
            CGFloat statusBarHeight = [[UIApplication sharedApplication] statusBarFrame].size.height;
            // 导航栏高度
            CGFloat navigationHeight = 0;
            
            WKSnapshotConfiguration *shotConfiguration = [[WKSnapshotConfiguration alloc] init];
            // 仅截图检测导航栏以下部分内容(底部安全区域不影响)
            shotConfiguration.rect = CGRectMake(0, statusBarHeight + navigationHeight, webview.bounds.size.width, (webview.bounds.size.height - navigationHeight - statusBarHeight));
            @weakify(self);
            [webview takeSnapshotWithConfiguration:shotConfiguration completionHandler:^(UIImage * _Nullable snapshotImage, NSError * _Nullable error) {
                @strongify(self);
                if (snapshotImage) {
                    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99%认定为白屏
- (BOOL)searchEveryPixel:(UIImage *)image {
    CGImageRef cgImage = [image CGImage];
    size_t width = CGImageGetWidth(cgImage);
    size_t height = CGImageGetHeight(cgImage);
    // 每个像素点包含r g b a 四个字节
    size_t bytesPerRow = CGImageGetBytesPerRow(cgImage);
    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);
            
            totalCount ++;
            if (red >= 254 && green >= 254 && blue >= 254) {
                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 > 0.99) {
        return YES;
    } else {
        return NO;
    }
}

// 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;
    }
}

//补充:相关代码我给补上吧

#ifndef keywordify
#if DEBUG
#define keywordify autoreleasepool {}
#else
#define keywordify try {} @catch (...) {}
#endif
#endif

#ifndef weakify
#if __has_feature(objc_arc)
#define weakify(object) keywordify __weak __typeof__(object) object##_##weak_ = object;
#else
#define weakify(object) keywordify __block __typeof__(object) object##_##block_ = object;
#endif
#endif

#ifndef strongify
#if __has_feature(objc_arc)
#define strongify(object) keywordify __typeof__(object) object = object##_##weak_;
#else
#define strongify(object) keywordify __typeof__(object) object = object##_##block_;
#endif
#endif


typedef NS_ENUM(NSUInteger, webviewLoadingStatus) {
    WebViewNormalStatus,
    WebViewPendStatus,
    WebViewErrorStatus,
};

神奇的居然不白屏了，然而高兴还是早了，只是偶尔不白屏，大概率还是白屏。而且白屏时候会回调：

- (void)webView:(WKWebView *) webView didFailProvisionalNavigation: (WKNavigation *) navigation withError: (NSError *) error

还不错，至少有个报错信息了：

Error Domain=kCFErrorDomainCFNetwork Code=1 "(null)" UserInfo={_NSURLErrorFailingURLSessionTaskErrorKey=LocalDataTask <6A1A8E7A-A2BC-41CC-B1BE-A698457A75B2>.<1>, _WKRecoveryAttempterErrorKey=<WKReloadFrameErrorRecoveryAttempter: 0x2815f11c0>}

第五步：根据第四步报错信息，找到个链接，然后查看WKWebView.h，发现一个有希望的API：

- (nullable WKNavigation *)loadFileURL:(NSURL *)URL allowingReadAccessToURL:(NSURL *)readAccessURL

kCFErrorDomainCFNetwork (error code 1) in real device but no in simulator · Issue #396 · react-native-webview/react-native-webview · GitHub

尝试修改

NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:30];
NSString*documentPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES).firstObject;            

[WebView loadFileURL:request.URL allowingReadAccessToURL:[NSURL fileURLWithPath:documentPath]];

终于不白屏了，虽然加载的慢点。

如果还有其他办法欢迎补充，共同进步。