UI Eventing Android Demo

Overview

A Demo app built to show off an assortment of options for handling UI or One Time Events on Android (e.g. showing a snackbar or prompting navigation)

Demonstrated Methods

• Callbacks
• Mark on Send
• Fire and Forget
• Mark on Consume
• Events as State

Callbacks

• Passing an implementation of a Callback Interface from the View to the ViewModel
• Considerations
  • Tight Coupling
  • Requires Full Implementation
  • No Guarantees of Call
  • Need to Ensure Life-Cycle Aware

Mark on Send

• Once the Event has been sent, the ViewModel records that the event has been sent without View confirmation
• Considerations
  • Loose Coupling
  • No Guarantee of Consumption
  • Flexibility in Determining Sent
  • Verbose

Fire and Forget

• The ViewModel sends the event immediately upon creation, neither the View or ViewModel tracks the event
• Considerations
  • Loose Coupling
  • No Guarantee of Consumption
  • No Flexibility Determining Sent
  • Low Effort to Implement

Mark on Consume

• The ViewModel maintains the sent event until the View notifies the ViewModel that the event has been handled
• Considerations
  • Loose Coupling
  • Guarantee of Consumption
  • Flexibility Determining Sent
  • Verbose

Events as State

• The ViewModel doesn't maintain the idea of events, but instead treats everything as state, the View calls the ViewModel to notify it if state needs changed
• Considerations
  • Loose Coupling
  • Highly Reusable
  • Guarantee of Consumption
  • Verbose

Other Resources

• Android Developers - UI events
• Android SingleLiveEvent Redux with Kotlin Flow
• ViewModel: One-off event antipatterns
• Sending ViewModel Events to the UI in Android