Technical Q&A QA1703

Screen Capture in UIKit Applications

Q:  How do I take a screenshot in my UIKit application?

A: Every UIWindow (inherited from UIView) and UIView is backed by a CALayer. The CALayer/-renderInContext: method lets you render a layer and its sublayers to a graphics context. So, to grab a snapshot of the entire screen, you can iterate through each window on the screen and render its layer hierarchy to a destination context. Once finished you can get the screenshot image via the UIGraphicsGetImageFromCurrentImageContext function, as shown below.

Note that, CALayer/-renderInContext: captures only your UIKit and Quartz drawing. It does not capture OpenGL ES or video content. See the following Q&A's for how to capture OpenGL ES and camera content using relevant techniques:

OpenGL ES View Snapshot

How to capture video frames from the camera as images using AV Foundation

How do I take a screenshot of my app that contains both UIKit and Camera elements

To use Core Animation APIs, you need to add the QuartzCore framework in your Xcode project and include the QuartzCore header as shown in the following listing:

Listing 1  Include the QuartzCore header

#import <QuartzCore/QuartzCore.h>

Listing 2  Get a screenshot image

- (UIImage*)screenshot
    // Create a graphics context with the target size
    // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
    // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
    CGSize imageSize = [[UIScreen mainScreen] bounds].size;
    if (NULL != UIGraphicsBeginImageContextWithOptions)
        UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    // Iterate over every window from back to front
    for (UIWindow *window in [[UIApplication sharedApplication] windows])
        if (![window respondsToSelector:@selector(screen)] || [window screen] == [UIScreen mainScreen])
            // -renderInContext: renders in the coordinate space of the layer,
            // so we must first apply the layer's geometry to the graphics context
            // Center the context around the window's anchor point
            CGContextTranslateCTM(context, [window center].x, [window center].y);
            // Apply the window's transform about the anchor point
            CGContextConcatCTM(context, [window transform]);
            // Offset by the portion of the bounds left of and above the anchor point
                                  -[window bounds].size.width * [[window layer] anchorPoint].x,
                                  -[window bounds].size.height * [[window layer] anchorPoint].y);
            // Render the layer hierarchy to the current context
            [[window layer] renderInContext:context];
            // Restore the context
    // Retrieve the screenshot image
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    return image;

Document Revision History


Added links to other screenshot Q&A's. Pointed out that one needs to add the QuartzCore framework and include the QuartzCore header to use Core Animation APIs.


New document that demonstrates how to take a screenshot in an UIKit application