Convert UIWebview contents to a UIImage

问题:

I am using a UIWebView to display HTML formatted text. I am not loading a webpage, just supplying a string of HTML to the UIWebView.

Now I want to animate this UIWebView on screen, actually several of them (2-10 at a time). UIWebView is a little heavy, and although I haven't attempted it yet, I am planning for the worst. (I don't think this is premature optimization, I 'm almost positive this will be an issue)

To get around the problem, I figured I could convert the contents of the UIWebViews to UIImages and animate them instead.

So, my questions are:

1. How do you convert UIWebview contents to a UIImage (or CGImageRef)?
2. My UIWebViews have transparent bacgrounds, will the transparency be carried over to the UIImage?

Thanks for any suggestions

回答1:

UIGraphicsBeginImageContext(webview.bounds.size);
[webview.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

You might run into issues if the webview dimensions are large because the webview uses a CATiledLayer that doesn't draw everything for memory reasons.

The image will include transparency

回答2:

I could be wrong but if you set the cache param of CoreAnimation the OS will handle this optimisation for you.

e.g.

[UIView setAnimationTransition:transition forView:self.view cache:YES];