Changes the background image of the group container to the image in the specified data object.
- watchOS 2.0+
A data object containing the image data in its native format. Specifying
nilremoves the existing image, causing the watch interface to display nothing in the space previously occupied by the image.
Use this method when you already have image data in the raw PNG or JPG format. This method sends the data as-is, which lets you send the data in a compressed format. Sending compressed data is often more efficient than sending a