能否将NSTreeNode以CKRecordValueStore形式存储至CloudKit？

Absolutely, there are practical ways to persist an NSTreeNode structure using CKRecordValueStore for CloudKit. The key here is that NSTreeNode isn’t a native CKRecordValue type, so we need to serialize it into a format CloudKit understands, then reverse the process when retrieving it. Let’s walk through the steps:

Step 1: Serialize NSTreeNode to a CloudKit-compatible Dictionary #

First, we’ll convert the tree structure into a nested dictionary—this works because CloudKit supports nested dictionaries as long as all leaf values are valid CKRecordValue types (strings, numbers, Data, dates, CKReference, etc.). We’ll use recursion to traverse the tree:

func serializeTreeNode(_ node: NSTreeNode) -> [String: Any] {
    var nodeDict: [String: Any] = [:]
    
    // Handle the node's represented object
    if let contentDict = node.representedObject as? [String: Any] {
        nodeDict["content"] = contentDict
    } else if let codableContent = node.representedObject as? Codable {
        // If your content is a custom Codable type, encode it to Data
        let encoder = JSONEncoder()
        if let contentData = try? encoder.encode(codableContent) {
            nodeDict["contentData"] = contentData
        }
    }
    
    // Recursively serialize child nodes
    let childDicts = node.children?.map(serializeTreeNode) ?? []
    nodeDict["children"] = childDicts
    
    return nodeDict
}

Step 2: Store the Serialized Tree in CKRecordValueStore #

Once you have the serialized dictionary, you can directly store it in your CKRecordValueStore instance:

// Assume you have an existing CKRecord and CKRecordValueStore
let targetRecord = CKRecord(recordType: "TreeRecords")
let valueStore = CKRecordValueStore(record: targetRecord)

// Serialize your root NSTreeNode
let rootTreeNode = yourRootNSTreeNodeInstance
let serializedTree = serializeTreeNode(rootTreeNode)

// Save to the value store
do {
    try valueStore.setObject(serializedTree, forKey: "treeStructure")
    // Don't forget to save the CKRecord to CloudKit afterward!
} catch {
    print("Failed to save tree structure: \(error.localizedDescription)")
}

Step 3: Deserialize the Dictionary Back to NSTreeNode #

To retrieve the tree, reverse the process with another recursive function to rebuild the NSTreeNode hierarchy:

func deserializeTreeNode(from dict: [String: Any]) -> NSTreeNode? {
    let node = NSTreeNode()
    
    // Restore the represented object
    if let contentDict = dict["content"] as? [String: Any] {
        node.representedObject = contentDict
    } else if let contentData = dict["contentData"] as? Data {
        // Replace YourCustomCodableType with your actual type
        if let decodedContent = try? JSONDecoder().decode(YourCustomCodableType.self, from: contentData) {
            node.representedObject = decodedContent
        }
    }
    
    // Restore child nodes
    if let childDicts = dict["children"] as? [[String: Any]] {
        node.children = childDicts.compactMap(deserializeTreeNode)
    }
    
    return node
}

// Retrieve and restore the tree
if let serializedTree = valueStore.object(forKey: "treeStructure") as? [String: Any],
   let restoredRootNode = deserializeTreeNode(from: serializedTree) {
    // You now have your original NSTreeNode hierarchy back!
}

Key Considerations #

• Valid Content Types: Ensure your representedObject can be converted to a CKRecordValue-compatible type. For custom objects, using Codable to encode to Data is the most reliable approach.
• Tree Depth: If your tree is extremely deep, recursive functions might hit stack overflow. In that case, switch to an iterative traversal approach for serialization/deserialization.
• Record Size Limits: CloudKit restricts single records to ~1MB. If your serialized tree exceeds this, split it into multiple records and use CKReference to link parent/child nodes.

内容的提问来源于stack exchange，提问作者Muhammad Awais