image set has an unassigned child
In the asset catalog's Attributes inspector, check some checkboxes, like Universal or iPhone and iPad. Now you will see slots for the resolutions such as "1x", "2x", and "3x". Those slots are where your images need to go.
I know this is an old one, but recently I got this problem after I merged 2 branches and encountered conflicts. 2 problems :
- I got this warning and could not see anything in the attributes inspector.
- However I resolved the conflicts it just doesn't seem to work.
All you have to do is Clean build your Xcode. Navigate away from .xcassets. Come back to .xcassets, you should be seeing the attributes inspector now.
Check the scales option. I previously had it to single scale but now it was changed to individual scales. On changing it back I got another row in the image set stating Unassigned. I just dragged this to the single scale row. And woila !