how to take a screenshot of the iPhone programmatically?

Question

Is it possible in objective C that we can take the screen shot of screen and stored this image in UIImage.

Answer 1

The previous code assumes that the view to be captured lives on the main screen...it might not.

Would this work to always capture the content of the main window? (warning: compiled in StackOverflow)

- (UIImage *) captureScreen {
    UIWindow *keyWindow = [[UIApplication sharedApplication] keyWindow];
    CGRect rect = [keyWindow bounds];
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [keyWindow.layer renderInContext:context];   
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;
}

Answer 2

You need to create a bitmap context of the size of your screen and use

[self.view.layer renderInContext:c]

to copy your view in it. Once this is done, you can use

CGBitmapContextCreateImage(c)

to create a CGImage from your context.

Elaboration :

CGSize screenSize = [[UIScreen mainScreen] applicationFrame].size;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB(); 
CGContextRef ctx = CGBitmapContextCreate(nil, screenSize.width, screenSize.height, 8, 4*(int)screenSize.width, colorSpaceRef, kCGImageAlphaPremultipliedLast);
CGContextTranslateCTM(ctx, 0.0, screenSize.height);
CGContextScaleCTM(ctx, 1.0, -1.0);

[(CALayer*)self.view.layer renderInContext:ctx];

CGImageRef cgImage = CGBitmapContextCreateImage(ctx);
UIImage *image = [UIImage imageWithCGImage:cgImage];
CGImageRelease(cgImage);
CGContextRelease(ctx);  
[UIImageJPEGRepresentation(image, 1.0) writeToFile:@"screen.jpg" atomically:NO];

Note that if you run your code in response to a click on a UIButton, your image will shows that button pressed.