To better support a responsive UI experience, the framework provides a waiting spinner and loading message on the gallery’s dropdown when it is trying to asynchronously load a large number of items. The loading message can be updated at runtime or set statically using the loadingMessage attribute. Note, to get this default behavior, no heavy code should be put in the gallery’s constructor since it will block the UI thread and prevent the spinner from showing up. The loading message only appears in drop down galleries (not in-inline).
Target Platforms: Windows 10, Windows 8.1