Posting to LiveData from Coroutine to Update UI even if LiveData Will Only Update Once

In my ViewModel's constructor, I immediately launch a coroutine to make a one time network call. To update the UI based on the result of this network call, I post updates to a few LiveData variables in my ViewModel. These LiveData variables are, in turn, observed by a fragment which then make the necessary UI updates.

What I'm wondering is if this is a valid way to make UI updates from a coroutine. As I mentioned earlier, the network request is only a one time thing done upon initialization, and so the LiveData variables will never be updated more than once. Is it then wasteful to set up observers in my fragment since I know for a fact they will only be called once? If so, what would be a better way to do this?

Thanks!

Solution

Is it then wasteful to set up observers in my fragment since I know for a fact they will only be called once?

They may be called more than once.

Primarily, LiveData is a value holder. And, specifically, by having LiveData in a ViewModel, you retain the LiveData and the held values across configuration changes (screen rotations, dark mode switch, etc.).

So, the flow may wind up being:

Your fragment is created
Your viewmodel is created and you kick off the network I/O
Your fragment instantiates its UI
Your fragment observes the LiveData
Your coroutine completes and your viewmodel updates the LiveData
Your fragment receives the value from the LiveData and updates the UI
The user twists her wrist and rotates the screen
Your fragment is destroyed
Your replacement fragment is created
Your viewmodel is retained, and your replacement fragment gets that same viewmodel with the same LiveData
Your replacement fragment instantiates its UI
Your replacement fragment observes the LiveData
Your replacement fragment receives the value from the LiveData and updates the UI

So, what you are describing is generally reasonable.