Swift4：“MessageKind”没有成员“url”

下面是 MessageKit 库的示例代码。目前，其行为是所有图像消息必须在显示给最终用户之前完全加载，因此需要花费大量时间等待。我想要的是在加载所有消息后加载图像。

看 1/ 你会看到“kind”变量将是一个 mediaItem 看2/你会看到mediaItem有“url”变量 看3/你会看到消息是用上面的mediaItem创建的

问题是如何获取3/处消息的url？我在下面尝试过，但斯威夫特不明白

let imkind = message.kind
imkind.photo.url // error Enum element 'photo' cannot be referenced as an instance member

以下为 1/ 2/ 3/

1/消息类型协议

public protocol MessageType {

    /// The sender of the message.
    var sender: Sender { get }

    /// The unique identifier for the message.
    var messageId: String { get }

    /// The date the message was sent.
    var sentDate: Date { get }

    /// The kind of message and its underlying kind.
    var kind: MessageKind { get }

}

2/ 创建一个图像放入消息中，如下所示：

private struct ImageMediaItem: MediaItem {

    var url: URL?
    var image: UIImage?
    var placeholderImage: UIImage
    var size: CGSize

    init(image: UIImage) {
        self.image = image
        self.size = CGSize(width: 240, height: 240)
        self.placeholderImage = UIImage()
    }

}

3/ 根据上面的MessageType创建一条消息：

internal struct MockMessage: MessageType {

    var messageId: String
    var sender: Sender
    var sentDate: Date
    var kind: MessageKind

    private init(kind: MessageKind, sender: Sender, messageId: String, date: Date) {
        self.kind = kind
        self.sender = sender
        self.messageId = messageId
        self.sentDate = date
    }

    init(image: UIImage, sender: Sender, messageId: String, date: Date) {
        let mediaItem = ImageMediaItem(image: image)
        self.init(kind: .photo(mediaItem), sender: sender, messageId: messageId, date: date)
    }

}

4/ pod库中的messageKind

/// An enum representing the kind of message and its underlying kind.
public enum MessageKind {

    /// A standard text message.
    ///
    /// - Note: The font used for this message will be the value of the
    /// `messageLabelFont` property in the `MessagesCollectionViewFlowLayout` object.
    ///
    /// Using `MessageKind.attributedText(NSAttributedString)` doesn't require you
    /// to set this property and results in higher performance.
    case text(String)

    /// A message with attributed text.
    case attributedText(NSAttributedString)

    /// A photo message.
    case photo(MediaItem)

    /// A video message.
    case video(MediaItem)

    /// A location message.
    case location(LocationItem)

    /// An emoji message.
    case emoji(String)

    /// A custom message.
    /// - Note: Using this case requires that you implement the following methods and handle this case:
    ///   - MessagesDataSource: customCell(for message: MessageType, at indexPath: IndexPath, in messagesCollectionView: MessagesCollectionView) -> UICollectionViewCell
    ///   - MessagesLayoutDelegate: customCellSizeCalculator(for message: MessageType, at indexPath: IndexPath, in messagesCollectionView: MessagesCollectionView) -> CellSizeCalculator
    case custom(Any?)

}

guard case .photo(let mediaItem) = imkind else {
        return
    }

    print(mediaItem.url)

您必须使用此代码解开枚举大小写。问题是您尝试将枚举检索为 mediaItem。但你必须检索内部数据。