Android Studio 3.0 xml-layout file's preview not showing

Cleaning and rebuilding my project solved the issue.

try different theme (may be from Appcompat) and API level from top

OR

1. If you have made some changes in the layout just undo it.
2. delete .idea and .gradle folder from root of the project
3. close android studio , restart it
4. click on gradle icon from right sidebar and click sync icon to refresh project. now rebuild the project and it should work.

After a lot searching and I tried all solution which people give here, but any of them didn't solve my problem, I guess this problem is from studio's developers, and they may fix it in next patch. so I simply re-installed my android studio and it's solved.