不管是UIWebView还是WKWebView，都是key在webView初始化完成的时候添加KVO，用来监听webView的contentSize变化，添加KVO：

[webView.scrollView addObserver:self forKeyPath:@"contentSize" options:NSKeyValueObservingOptionNew context:nil];

KVO的监听方法

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context{
    
    if ([keyPath isEqualToString:@"contentSize"]) {
        
        CGSize fittingSize = [_wvDetails sizeThatFits:CGSizeZero];
        _wvDetails.frame = CGRectMake(0, 0, Screen_Width, fittingSize.height);
        [_tvList reloadData];
        
    }
    
}

在退出当前页面的时候，记得一定要移除监听，不然就崩

- (void)dealloc{
    [_wvDetails.scrollView removeObserver:self forKeyPath:@"contentSize"];
}