demo can not match the `xml` file with `activity` file

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demo has error : every id can not be referred in the activity.kt file.

For example in the CameraActivity.kt file,setContentView(R.layout.activity_camera) shows error: Unresolved reference: activity_camera. And every id in the activity_camera.xml file can not be referred, so as all other xml files.

Version used

CameraView version : 2.7.2

What's wrong in this situation? Thanks!