Take screen-shot of current-application-window.

takeScreenshot.m

// a function to take screen-shot of application's screen
- (UIImage*)takeScreenshot
{
    // get the key-window references
    UIWindow *keyWindow = [[UIApplication sharedApplication] keyWindow];
    
    // manipulate boundries of key-window
    CGRect rect = [keyWindow bounds];
    
    // create context using size
    UIGraphicsBeginImageContextWithOptions(rect.size,YES,0.0f);
    
    // get the context reference
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    // render in context
    [keyWindow.layer renderInContext:context];
    
    // get the rendered image
    UIImage *capturedScreen = UIGraphicsGetImageFromCurrentImageContext();
    
    // complete context
    UIGraphicsEndImageContext();
    
    // return image
    return takeScreenshot;
}
// -------------------------------------------------