Reused UIWebView showing previous loaded content for a brief second on iPhone

Question

In one of my apps I reuse a webview. Each time the user enters a certain view on reload cached data to the webview using the method - (void)loadData:(NSData *)data MIMEType:(NSString *)MIMEType textEncodingName:(NSString *)encodingName baseURL:(NSURL *)baseURL and I wait for the callback call - (void) webViewDidFinishLoad:(UIWebView *)webView. In the mean time I hide the webview and show a 'loading' label. Only when I receive webViewDidFinishLoad do I show the webview.

Many times what happens is I see the previous data that was loaded to the webview for a brief second before the new data I loaded kicks in.

I already added a delay of 0.2 seconds before showing the webview but it didn't help.

Instead of solving this by adding more time to the delay does anyone know how to solve this issue or maybe clear old data from a webview without release and allocating it every time?

Answer 1

First, the UIWebView renders it contents in a background thread. Even when you receive webViewDidFinishLoad: it might not be completely done. Specially if it is an ajax-intense page that comes from the network.

You say you are hiding the view. I wonder if that means that the webview delays its drawing completely. What you could try is to move the UIWebView offscreen or obscure it with another view. Maybe that will change it's drawing behaviour.

If you do not need an interactive UIWebView then you can also consider to do it completely offscreen in a separate UIWindow and then create an image from that UIWebView's layer.

Answer 2

Try loading a local file that is blank or has a loading graphic when you hide it, rather than just loading new content when you show it. Since the file is local it will be quick and even if the new page takes a while to load it will have either blank or loading expected behavior.