从Swift中的NSTextField获取NSImage

Question

我曾经从Obj-C中检索NSTextField的子类中的NSImage，如下所示：

  NSDictionary *attributedVal = [[self attributedStringValue] attributesAtIndex:i effectiveRange:&effectiveRange];
  if ([[attributedVal allKeys] containsObject:NSAttachmentAttributeName]) {
    NSTextAttachment *attachment = [attributedVal valueForKey:NSAttachmentAttributeName];
    NSCell *attachmentCell = (NSCell *)[attachment attachmentCell];
    ... [[attachmentCell image] name] ...
  } 

当我尝试在Swift中执行相同操作时，我似乎无法转换attachmentCell但是会​​出现编译错误：

  let attributedVal = attributedStringValue.attributesAtIndex(i, effectiveRange: effectiveRange)
  if let attachment = attributedVal[NSAttachmentAttributeName] as? NSTextAttachment {
    let attachmentCell = attachment.attachmentCell as NSCell // does not work
    ...
  }

Answer 1

感谢Nate Cook。以下作品：

  let attributedVal = attributedStringValue.attributesAtIndex(i, effectiveRange: effectiveRange)
  if let attachment = attributedVal[NSAttachmentAttributeName] as? NSTextAttachment {
    let attachmentCell = attachment.attachmentCell as NSTextAttachmentCell
    let image = attachmentCell.image
    ...
  }