Dynamically load Collada files in SceneKit at runtime

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self downloadZip];
}

- (void)downloadZip {
    
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:configuration];
    
    NSURL *URL = [NSURL URLWithString:@"http://www.the-nerd.be/product-1-optimized.scnassets.zip"];
    NSURLRequest *request = [NSURLRequest requestWithURL:URL];
    
    NSURLSessionDownloadTask *downloadTask = [manager downloadTaskWithRequest:request progress:nil destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {
        NSURL *documentsDirectoryURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
        return [documentsDirectoryURL URLByAppendingPathComponent:[response suggestedFilename]];
    } completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {
        NSLog(@"File downloaded to: %@", filePath);
        
        // Unzip the archive
        NSArray  *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];
        NSString *inputPath = [documentsDirectory stringByAppendingPathComponent:@"/product-1-optimized.scnassets.zip"];
        
        NSError *zipError = nil;
        
        [SSZipArchive unzipFileAtPath:inputPath toDestination:documentsDirectory overwrite:YES password:nil error:&zipError];
        
        if( zipError ){
            NSLog(@"[GameVC] Something went wrong while unzipping: %@", zipError.debugDescription);
        }else {
            NSLog(@"[GameVC] Archive unzipped successfully");
            [self startScene];
        }
        
    }];
    [downloadTask resume];
    
}

// Load the downloaded scene
NSURL *documentsDirectoryURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
    documentsDirectoryURL = [documentsDirectoryURL URLByAppendingPathComponent:@"product-1-optimized.scnassets/cube.dae"];
    
SCNSceneSource *sceneSource = [SCNSceneSource sceneSourceWithURL:documentsDirectoryURL options:nil];

After this we can just get a reference to the Cube node in our Collada file with the following line of code.  The identifier is the name you gave the 3D object in your 3D program. In my case it was 'Cube'.

// Get reference to the cube node
SCNNode *theCube = [sceneSource entryWithIdentifier:@"Cube" withClass:[SCNNode class]];

Last bit is create an empty scene, set up a camera and add a light.

// Create a new scene
SCNScene *scene = [SCNScene scene];
    
// create and add a camera to the scene
SCNNode *cameraNode = [SCNNode node];
cameraNode.camera = [SCNCamera camera];
[scene.rootNode addChildNode:cameraNode];
    
// place the camera
cameraNode.position = SCNVector3Make(0, 0, 15);
    
// create and add a light to the scene
SCNNode *lightNode = [SCNNode node];
lightNode.light = [SCNLight light];
lightNode.light.type = SCNLightTypeOmni;
lightNode.position = SCNVector3Make(0, 10, 10);
[scene.rootNode addChildNode:lightNode];
    
// create and add an ambient light to the scene
SCNNode *ambientLightNode = [SCNNode node];
ambientLightNode.light = [SCNLight light];
ambientLightNode.light.type = SCNLightTypeAmbient;
ambientLightNode.light.color = [UIColor darkGrayColor];
[scene.rootNode addChildNode:ambientLightNode];

Final step ... add the cube to the scene with this line of code.

// Add our cube to the scene
[scene.rootNode addChildNode:theCube];

And lets put the scene in a SCNView object, so we can show it.

// retrieve the SCNView
SCNView *scnView = (SCNView *)self.view;

// set the scene to the view
scnView.scene = scene;

// allows the user to manipulate the camera
scnView.allowsCameraControl = YES;

// show statistics such as fps and timing information
scnView.showsStatistics = YES;

// configure the view
scnView.backgroundColor = [UIColor blackColor];