adb manager unable to locate adb code example

Example 1: android studio unable to locate adb

[Ctrl + Alt + Shift + S]
Project Settings > Project > Project DSK   (choose)

Example 2: Unable to locate adb

In my case I had no SDK selected for my project(not sure why). Simply went to 
Project Structure dialog (alt+ctrl+shift+s or button 1 on the screen) and then 
to project-> Project SDK's was selected <no SDK>. Just changed it to the latest

refrence:
https://stackoverflow.com/questions/27301960/errorunable-to-locate-adb-within-sdk-in-android-studio/62490637#62490637