Which version of OSX ?
Have a look here if not already done, it is said that those keys are not implemented…
.customIconKeysimply isn’t implemented (r. 6508029). Depending on your needs, you may be able to use
.effectiveIconKey, which does take into account any custom icon.
I wasn’t able to track down a definitive answer about
.thumbnailKey, but I suspect that it is similarly unimplemented. If you file a bug about
.thumbnailKeyand then post the bug number, I may be able to find out more.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"