make a screenshot and save it into UIImage

screenshot

 UIWindow *window = [UIApplication sharedApplication].keyWindow;
    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
        UIGraphicsBeginImageContextWithOptions(window.bounds.size, NO, [UIScreen mainScreen].scale);
    }
    else {
        UIGraphicsBeginImageContext(window.bounds.size);
    }
    if ([window respondsToSelector:@selector(drawViewHierarchyInRect:afterScreenUpdates:)]) {
        [window drawViewHierarchyInRect:window.bounds afterScreenUpdates:YES];
    }
    else {
        [window.layer renderInContext:UIGraphicsGetCurrentContext()];
    }
    UIImage *scImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();