How to capture current view screenshot and reuse in code? (iPhone SDK)

Question

I am attemting to transition from one UIView to another, when the user rotates the device. This, in of itself, is not difficult. However, since I am displaying completely di

Answer 1

- (UIImage *)captureView:(UIView *)view {
    CGRect screenRect = [[UIScreen mainScreen] bounds];

    UIGraphicsBeginImageContext(screenRect.size);

    CGContextRef ctx = UIGraphicsGetCurrentContext();
    [[UIColor blackColor] set];
    CGContextFillRect(ctx, screenRect);

    [view.layer renderInContext:ctx];

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return newImage;
}

Found this here :

http://discussions.apple.com/thread.jspa?messageID=8358740

Answer 2

This code worked for me

- (UIImage *)captureScreenInRect:(CGRect)captureFrame {
    CALayer *layer;
    layer = self.view.layer;
    UIGraphicsBeginImageContext(self.view.bounds.size); 
    CGContextClipToRect (UIGraphicsGetCurrentContext(),captureFrame);
    [layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *screenImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return screenImage;
}

Answer 3

On Mac this is so easy... you just need -bitmapImageRepForCachingDisplayInRect:, but of course iPhone has no such thing.

I think I would attack this by setting up a graphics context and calling [window drawRect:...] on it to capture the current image of the screen. This is a bit out of spec, because you're not really supposed to go calling -drawRect: yourself. I'd be a bit nervous of side-effects on doing this, but it may be fine. If it's a full-screen view you control, you could of course hoist the drawing code out of -drawRect: so you're not calling that directly.

A similar approach would be to use CALayer -drawInContext: of the current -presentationLayer. That might be slightly more "in spec" since it's legal to pass that your own context. But I don't know if you'd actually be able to get all the sub-views correctly. Might depend on the nature of your UIWindow.

Anyway, great question. Maybe someone has a more clever solution, but this is the way I'd attack it.

EDIT: Thanks to Rob Terrell, and his clever UIApplication+TVOut.m, I was introduced to the private method UIGetScreenImage() which returns a CGImageRef. If you're willing to go to private methods, that's a nice option for you. Given its name and functionality, it looks pretty stable to me and seems unlikely to violate Apple's intent. I also bumped into a pretty nice discussion on Air Source. Read through the comments for several links.

Answer 4

I can guarantee you [window drawRect:] won't work. Most views don't implement drawRect: and it's certainly not recursive like on the mac.

drawInContext: is also pretty much hosed simalarly, as it's fundamentally asking the layer to draw itself, not its sublayers recursively. "Default implementation does nothing." says it all.

I implementing this for the Clif Bar Save Our Snow app in the app store by doing the following:

• Walk the layer hierarchy recursively, getting the contents from each layer. If it smells like an image, use the CGContext methods to draw it into your context.
• While walking, make sure to apply the transformations/positions of each layer as you call recursively

Yes, a rather large pain in the ass. But yes, it works pretty well and got through by Apple :).