code: private static PBXObjectRef createPBXFileReference(final String sourceTree, final String baseDir, final File file) {
      final Map map = new HashMap();
      map.put("isa", "PBXFileReference");
  
      final String relPath = CUtil.toUnixPath(CUtil.getRelativePath(baseDir, file));
      map.put("path", relPath);
      map.put("name", file.getName());
      map.put("sourceTree", sourceTree);
      return new PBXObjectRef(map);
    }
docs: Create PBXFileReference.
  
  @param sourceTree
  source tree.
  @param baseDir
  base directory.
  @param file
  file.
  @return PBXFileReference object.