在Swift中对JSQMessageMediaData进行子类化

Question

我正在尝试在Swift中创建自定义消息媒体数据，但它一直告诉我：

type 'CustomMedia' does not conform to protocol 'NSObjectProtocol'

即使我已经实现了所有协议方法。缺少什么？

class CustomMedia: JSQMessageMediaData {

@objc func mediaView() -> UIView! {
    let mediaView = UIView()
    let label = UILabel(frame: CGRectMake(0, 0, 200, 21))
    label.center = CGPointMake(160, 284)
    label.textAlignment = NSTextAlignment.Center
    label.text = "I'am a test label"
    mediaView.addSubview(label)
    return mediaView
}

@objc func mediaViewDisplaySize() -> CGSize {
    let size = CGSizeMake(200, 21)
    return size
}


@objc func mediaPlaceholderView() -> UIView! {
    return nil
}

@objc func mediaHash() -> UInt {
    return UInt(0)
}
}