Adding Asset Catalogs to Projects
Asset catalogs that are members of a target are processed by Xcode during the build of that target. Use the Xcode app to add a manually generated asset catalog to a project. For information on how to do this, see Add files and folders to a project in Xcode Help. Note that the asset catalog does not need to be in the same folder hierarchy as the Xcode project.
Once the asset catalog is added, updates to your catalog are automatically included during the next build.