How to take a screenshot programmatically

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

    NSData * data = UIImagePNGRepresentation(image);

    [data writeToFile:@"foo.png" atomically:YES];

UPDATE April 2011: for retina display, change the first line into this:

if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
    UIGraphicsBeginImageContextWithOptions(self.window.bounds.size, NO, [UIScreen mainScreen].scale);
else
    UIGraphicsBeginImageContext(self.window.bounds.size);