ios - UICollectionView 内的 WebView 动态内容大小

Question

我试图通过引用 collectionViewCell 来调整 UICollectionViewCell 内 WKWebView 动态 HTML 内容的大小。工作正常，但有时在以下行解包可选值时会抛出意外发现的 nil:

let cell:CollectionViewCell = collectionView!.cellForItem(at: indexpath) as! CollectionViewCell

这是我的代码:

func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!)
{
        let indexpath: IndexPath = IndexPath.init(item: self.pageControl.currentPage, section: 0)
        let cell:CollectionViewCell = collectionView!.cellForItem(at: indexpath) as! CollectionViewCell
        cell.newsWebView?.evaluateJavaScript("document.readyState", completionHandler: { (result, error) in
            if result == nil || error != nil {
                return
            }
            cell.newsWebView?.evaluateJavaScript("document.body.offsetHeight", completionHandler: { (result, error) in
                if let height = result as? CGFloat {
                    cell.webviewHeightConstraint?.constant = height
                }
            })
    CustomeLoader.instance.hideLoader()
}

fatal error: unexpectedly found nil while unwrapping an Optional value

Answer 1

试试这个。此崩溃可能是由于渲染延迟造成的。

let when = DispatchTime.now() + 1
DispatchQueue.main.asyncAfter(deadline: when) {
       let indexpath: IndexPath = IndexPath.init(item: pageControl.currentPage, section: 0)
        let cell:CollectionViewCell = collectionView!.cellForItem(at: indexpath) as! CollectionViewCell
         cell.newsWebView.evaluateJavaScript("document.readyState", completionHandler: { (complete, error) in
            if complete != nil {
                cell.newsWebView.evaluateJavaScript("document.body.offsetHeight", completionHandler: { (height, error) in
                    cell.webviewHeightConstraint.constant = height as! CGFloat
                })
            }

        })         
}