function to convert a saved obj file to USDZ in objective-c

obj2usdz.mm

// path to documents directory to save our usdc file
NSString* usdcPath = [documentsDirectory stringByAppendingPathComponent:@"usdcExample.usdc"];
NSURL *usdcUrl = [NSURL fileURLWithPath: usdcPath];

// path to documents directory to save our final usdz file
NSString* usdzPath = [documentsDirectory stringByAppendingPathComponent:@"usdzExample.usdz"];
NSURL *usdzUrl = [NSURL fileURLWithPath:usdzPath];

// load the .obj file at filePath as an MDLAsset
NSURL *url = [NSURL fileURLWithPath:filePath];
MDLAsset *asset = [[MDLAsset alloc]initWithURL:url];

// ensure the MDLAsset can write the desired extensions

// NOTE: including for example purposes. 
// this is false, but ideally this would be true and would handle everything for us
if([MDLAsset canExportFileExtension:@"usdz"]){
  NSLog(@"able to export as usdz");
} else {
  NSLog(@"NOT able to export as usdz");
}

// usda is supported (USD ascii format)
if([MDLAsset canExportFileExtension:@"usda"]){
  NSLog(@"able to export as usda");
}

// usdc is supported (USD binary format)
if([MDLAsset canExportFileExtension:@"usdc"]){
  NSLog(@"able to export as usdc");

  // save the usdc file
  [asset exportAssetToURL:usdcUrl];
}

// rename the usdc to usdz because that's all it takes
NSError *renameErr;
NSFileManager *fm = [[NSFileManager alloc] init];
BOOL mvResult = [fm moveItemAtPath:usdcPath toPath:usdzPath error:& renameErr];
if(! mvResult){
  NSLog(@"Error renaming usdz file: %@", [renameErr localizedDescription]);
}

Anyone ever get this to work?