Swift4：“ MessageKind”没有成员“ URL”

Question

下面是MessageKit库的示例代码。当前，其行为是在向最终用户显示之前必须完全加载所有图像消息，因此需要大量时间等待。我想要的是在所有消息都已加载之后加载图像。

看1 /，您将看到“ kind”变量将是mediaItem 看2 /，您将看到mediaItem具有“ url”变量 看3 /，您将看到消息是使用上述mediaItem创建的

问题是如何在3 /处获取消息的URL？我在下面尝试过，但是迅速不明白

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

下面是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 /创建一个图像以放入消息Kind，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 /根据上述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 / messageKind在pod库中

/// 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?)



}

Answer 1

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

    print(mediaItem.url)

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

Answer 2

你可以使用 switch case，因为 MessageKind 是一个枚举

switch message.kind {
        case .photo(let photoItem):
            if let urlsel = photoItem.url{
                print(urlsel)    // here is your imageUrl
                
        }
        default:
            break
        }