UIWebView中的iframe显示空白屏幕？

Question

只有iframe没有加载到UIWebView中并显示空白的白屏吗？

我在html内的iframe代码：

<p>
    <iframe mce_src="https://www.facebook.com/plugins/post.php?href=https%3A%2F%2Fwww.facebook.com%2Fsanga.says%2Fposts%2F2547207028627242%3A0&amp;width=500" 
            style="border:none;overflow:hidden" 
            scrolling="no" 
            allowtransparency="true" 
            allow="encrypted-media" 
            src="https://www.facebook.com/plugins/post.php?href=https%3A%2F%2Fwww.facebook.com%2Fsanga.says%2Fposts%2F2547207028627242%3A0&amp;width=500" 
            width="500" 
            height="746" 
            frameborder="0">
    </iframe>
</p>


-(BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType{

    NSLog(@"request :%@",request.URL);

    if(navigationType == UIWebViewNavigationTypeLinkClicked){
        return YES;
    }

    if(![[request.URL description] isEqualToString:@"about:blank"]){

        if ([[request.URL description] containsString:@"https://www.youtube.com"]) {
            return YES;
        } else {
            return NO;
        }
    }

    return YES;
}