截屏方法

• (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;
  }