Hi I am trying to run it on API 21, But in FrameAnalyser.kt line no 164 'boundingBoxOverlay.invalidate()' will through exception.
Please help me I am a beginner Thanks in advance.

E/AndroidRuntime: FATAL EXCEPTION: Thread-3
Process: com.example.facerecognition, PID: 12921
android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:7809)
at android.view.ViewRootImpl.invalidateChildInParent(ViewRootImpl.java:1338)
at android.view.ViewGroup.invalidateChild(ViewGroup.java:5446)
at android.view.View.invalidateInternal(View.java:14749)
at android.view.View.invalidate(View.java:14713)
at android.view.View.invalidate(View.java:14697)
at com.example.facerecognition.FrameAnalyser$analyze$1$1.run(FrameAnalyser.kt:150)
at java.lang.Thread.run(Thread.java:762)