Returns the data for the specified image in PNG format
- iOS 2.0+
- tvOS 9.0+
- watchOS 2.0+
The original image data.
A data object containing the PNG data, or
nil if there was a problem generating the data. This function may return
nil if the image has no data or if the underlying
CGImage contains data in an unsupported bitmap format.
If the image object’s underlying image data has been purged, calling this function forces that data to be reloaded into memory.