LiveData+ViewModel Challenges

- when to use removeObservers?
- reuse LD in repo or create new instance per repo requet? i prefer to reuse
- use singleton repos?
- use single event? or LiveData.setValue(null)?
  - best practice: use Event class (see https://link.medium.com/qjuB2VGnoV)
- use live data or single event in repo?
  - if we don't reuse LD in repo, then we could use LD (single event is useless)
- observeForever is not implemented in single live event
  - mediators internally use observeForever
- Use a repo livedata in two view models:
  - it should be single but two VMs can't observe single LD
- a repo request should return:
  - corresponding live data?
  - void?
    - use a getter to get LD
  
  - who is responsible for navigation logic?
    - activity/fragment?
    - view model?
      - use command design pattern
        - a live data to emit commands
        - activty/fragment observes command live data and does the navigation
  
  problems:
    use-case:
      - single events in repo
      - two VMs listening on same single event
      - reusing LD
    solution1:
      - use removeObservers before triggering the repo request
        then observe repo LD, finally trigger repo request
    solution2:
      - don't reuse repo LDs, create new LD per repo request