Generating thumbnails of local webpages on iOS - ios

Question

I have a set of local HTML pages that I would like batch generate thumbnails for on the fly (I only want to show the thumbnails, not the full web pages). This is the way I'm accomplishing this:
NSString* path = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:link];
NSURL* url = [NSURL fileURLWithPath:path];
NSURLRequest* request = [NSURLRequest requestWithURL:url];
UIWebView* webView = [[UIWebView alloc] initWithFrame:CGRectMake(0, 0, 725, 1004)];
webView.delegate = cell;
[webView loadRequest:request];
[self.view addSubview:webView]; // doesn't work without this line, but then the UIWebView is onscreen
Then in the delegate:
- (void)webViewDidFinishLoad:(UIWebView *)webView
{
[self performSelector: #selector(render:) withObject: webView afterDelay: 0.01f];
}
- (void) render: (id) obj
{
UIWebView* webView = (UIWebView*) obj;
CGSize thumbsize = CGSizeMake(96,72);
UIGraphicsBeginImageContext(thumbsize);
CGContextRef context = UIGraphicsGetCurrentContext();
CGFloat scalingFactor = thumbsize.width/webView.frame.size.width;
CGContextScaleCTM(context, scalingFactor,scalingFactor);
[webView.layer renderInContext: context];
UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
self.thumbnail.image = resultImage;
}
Here are my questions:
1) Is my general approach correct? Is this the most efficient way to batch process thumbnails of webpages on the fly?
2) I want to be able to render the thumbnail from an offscreen UIWebView, but the webViewDidFinishLoad: doesn't get called unless I add the UIWebView to the view hierarchy. Is there a way I can avoid this?
3) If I attempt to capture an image of the UIWebView in webViewDidFinishLoad:, I get a blank image. I have to put an artificial delay for the capture to work. Any way around this?
Thanks!

Answer 1

1) This seems to be the only way I know of to do this, without relying on a third party server-based API (if one exists)
2) You can draw the UIWebView off-screen by setting its frame to a position that is off-screen. For example 320,568,725,1008. I haven't tested it, but you should even be able to set the view as a 1 x 1px frame.
3) I imagine this is because when webViewDidFinishLoad: is called, a SetNeedsDisplay() has been called on the web view, but the web view has not yet redrawn itself. I'm not sure about a way around this.