解决WKWebView加载网页url或者html内容，利用document.body.scrollHeight获取内容高度不准确问题

步骤：

1、用此种方式初始化

NSString *jScript = @"var meta = document.createElement('meta'); meta.setAttribute('name', 'viewport'); meta.setAttribute('content', 'width=device-width,maximum-scale=1, minimum-scale=1,user-scalable=no'); document.getElementsByTagName('head')[0].appendChild(meta); window.onload=function(){var imgs = document.getElementsByTagName('img');for (var i in imgs){imgs[i].style.maxWidth='100%';imgs[i].style.height='auto';}}";

        WKUserScript *wkUScript = [[WKUserScript alloc] initWithSource:jScript  injectionTime:WKUserScriptInjectionTimeAtDocumentEnd forMainFrameOnly:YES];

        WKUserContentController *wkUController = [[WKUserContentController alloc] init];

        [wkUControlleraddUserScript:wkUScript];

        WKWebViewConfiguration *wkWebConfig = [[WKWebViewConfiguration alloc] init];

        wkWebConfig.userContentController= wkUController;

        WKWebView * webView = [[WKWebView alloc] initWithFrame:CGRectZero configuration:wkWebConfig];

2、再在代理方法中设置：

- (void)webView:(WKWebView*)webView didFinishNavigation:(null_unspecified WKNavigation*)navigation{

[webView evaluateJavaScript:@"document.body.scrollHeight" completionHandler:^(id_Nullable result,NSError*_Nullable error){

        //获得的实际高度

        CGFloat scrollHeight = [result floatValue];

        //然后在此处理对应的高度

    }];

}