WKWebView高度约束导致约束错误

Question

我在UIView中有一个WKWebView。

这些是约束：

webContainerView.leftAnchor.constraint(equalTo: self.leftAnchor, constant: 0).isActive = true
webContainerView.rightAnchor.constraint(equalTo: self.rightAnchor, constant: 0).isActive = true
webContainerView.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: -10).isActive = true


contentWKWebView.navigationDelegate = self
contentWKWebView.leftAnchor.constraint(equalTo: self.webContainerView.leftAnchor, constant: 2).isActive = true
contentWKWebView.rightAnchor.constraint(equalTo: self.webContainerView.rightAnchor, constant: -2).isActive = true
contentWKWebView.topAnchor.constraint(equalTo: self.webContainerView.topAnchor, constant: 2).isActive = true
contentWKWebView.bottomAnchor.constraint(equalTo: self.webContainerView.bottomAnchor, constant: -2).isActive = true
webViewHeightConstraint = contentWKWebView.heightAnchor.constraint(equalToConstant: 100)
webViewHeightConstraint?.isActive = true // causes error

我必须为WKWebView设置一个初始高度大小，否则自动调整高度以适应内容将无法正常工作。

这是用于自动调整高度的代码：

extension MyCell: WKNavigationDelegate {
    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
        webView.evaluateJavaScript("document.documentElement.scrollHeight", completionHandler: { (height, error) in
            self.webViewHeightConstraint?.constant = height as! CGFloat
        })
    }
}

UIView和WKWebView是UITableViewCell的子视图。

有什么主意吗？

谢谢！