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iosswift5

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

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.

Solution

  • 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.