코틀린 네비게이션 참조 https://codechacha.com/ko/android-navigation-drawer/
kotlin bundle putString https://proandroiddev.com/code-clean-up-with-kotlin-19ee1c8c0719
https://developer.android.com/guide/navigation/navigation-pass-data
expandable cardview https://affineur.tistory.com/38
맵 안에 맵 넣는 방법 https://firebase.google.com/docs/firestore/manage-data/add-data
firestore get data https://firebase.google.com/docs/firestore/query-data/get-data
안드로이드 라이브러리 https://androidexample365.com/
dialog 중복 에러 https://stackoverflow.com/questions/59600561/how-to-call-removeview-on-the-childs-parent
countdown timer https://android--code.blogspot.com/2018/04/android-kotlin-countdowntimer-start.html
image view change https://stackoverflow.com/questions/23357706/how-to-check-which-current-image-resource-is-attached-to-imageview-in-android-xm
appbar 뒤로가기 nav_graph 등 https://codechacha.com/ko/android-navigation-basic/
timer 대신 사용하기 좋은 핸들러 https://www.youtube.com/watch?v=3pgGVBmSVq0
nav_graph https://codechacha.com/ko/android-navigation-basic/
simple get api from url https://stackoverflow.com/questions/47971972/how-to-properly-use-the-url-with-kotlin-android
안드로이드 json 파싱 https://codechacha.com/ko/how-to-parse-json-in-android/
메인스레드 ui 변경 https://dreamaz.tistory.com/268
파이어베이스 리얼타임 읽기 https://stack07142.tistory.com/282
어댑터 -> 메인프래그먼트 리스너 https://dreamaz.tistory.com/241
파이어베이스 여러팁 리얼채팅까지 https://cionman.tistory.com/72
리얼타임디비 체인지 힌트 https://minwook-shin.github.io/android-kotlin-service-firebase-database/
보상형광고 https://mynameisdabin.tistory.com/4
메인프래그먼트만 종료 https://jinunthing.tistory.com/22
동기처리 https://wooooooak.github.io/kotlin/2019/03/17/kotlin_coroutin/
앱종료 https://linkedlist.tistory.com/entry/Android%EC%96%B4%ED%94%8C%EC%9D%84-%EC%99%84%EC%A0%84-%EC%A2%85%EB%A3%8C%EC%8B%9C%EC%BC%9C%EB%B4%85%EC%8B%9C%EB%8B%A4-%EC%95%BD%EA%B0%84%EC%9D%98-%EC%8B%A4%ED%97%98
앱크기 줄이기 https://developer.android.com/topic/performance/reduce-apk-size