archivedObject(ofClass:from:) treats [SCNNode] differently that SCNNode-CodePudding

I have two methods, one to unarchive a root SCNNode, the other to unarchive an array of root SCNNode's (within a single file). This code for the solo node works:

guard let component = try? NSKeyedUnarchiver.unarchivedObject(ofClass: SCNNode.self, from: moleData)
    else {
        component = failNode
        return component    // return to moleFunc to abort?
    }

But when I try to retrieve an array of nodes, it doesn't work:

 guard let components = try? NSKeyedUnarchiver.unarchivedObject(ofClass: [SCNNode].self, from: moleData)
     else {
         components = []
         return components    // return to moleFunc to abort?
     }

In the above, unarchivedObject(ofClass:from:) two errors: Static method 'unarchivedObject(ofClass:from:)' requires that '[SCNNode]' conform to 'NSCoding' and Static method 'unarchivedObject(ofClass:from:)' requires that '[SCNNode]' inherit from 'NSObject'.

The form below will run OK but the operation fails to extract a useable array of nodes:

    guard let components = try? (NSKeyedUnarchiver.unarchivedObject(ofClass: NSArray.self, from: moleData) as! [SCNNode])
         else {
print("unarchivedObject(ofClass: FAIL, components = ", components)
             components = []
             return components    // return to moleFunc to abort
         }

The print, within the else, prints out as "[<SCNNode: 0x600001973600 | no child>]", the debugger shows zero elements.

The salient line from the Swift 3 implementation, which worked just fine, is:

components = (NSKeyedUnarchiver.unarchiveObject(withFile: filePath) as? [SCNNode])!

The node files all reside in the Bundle as plists.

I've no idea how to make the array version "conform" whereas the single SCNNode does just fine.

CodePudding user response：

The modern way to decode an array of SCNNode is by saying

let components = try? NSKeyedUnarchiver.unarchivedArrayOfObjects(ofClass: SCNNode.self, from: moleData)

That should work. If it doesn't, you'll have to just keep using the deprecated method; but I think it will.