I just migrated from OrbitMVI to Ballast. In 3mins...

# ballast

[ayodele]

I just migrated from OrbitMVI to Ballast. In 3mins. I like the "it just works" nature. Kudos.
I'm moving onto navigation with Ballast. If I'm not mistaken, it's built ontop on the redo and undo lib by the same author.
My question is do I still need compose navigation with Ballast navigation? If yes does ballast handle backstack??

[Casey Brooks]

A few things to unpack:

[Casey Brooks]

If I’m not mistaken, it’s built ontop on the redo and undo lib

ballast-navigation only depends on ballast-core, not ballast-undo. The backstack functionality is part of the navigation module itself. Out of the box, it allows you to do forward/lateral navigation to a specific destination, and to go backward to the previous destination. https://copper-leaf.github.io/ballast/wiki/modules/ballast-navigation/#step-4-navigate

Adding the undo/redo module to the Router allows you to handle returning to a screen after going backward, without referencing the Router itself. Normally, you can go back, but you cannot restore to the screen you just “went back from”. It adds the “forward” button of a browser’s address bar, which is not available in the base ballast-navigation module.

This might help illustrate the difference:

Without Undo/Redo module:

1. RouterContract.Inputs.GoToDestination(A)
    - Backstack: [A]
2. RouterContract.Inputs.GoToDestination(B)
    - Backstack: [A, B]
3. RouterContract.Inputs.GoBack()
    - Backstack: [A]
4. Cannot return to B, you have to do GoToDestination(B) again

With Undo/Redo module:

1. RouterContract.Inputs.GoToDestination(A)
    - State History:
        - Backstack: [A] (current state, destination is B)
2. RouterContract.Inputs.GoToDestination(B)
    - State History:
        - Backstack: [A]
        - Backstack: [A, B] (current state, destination is B)
3. UndoController.undo()
    - State History:
        - Backstack: [A] (current state, destination is A)
        - Backstack: [A, B]
4. UndoController.redo()
    - State History:
        - Backstack: [A]
        - Backstack: [A, B] (current state, destination is B once again)

The Compose Desktop example shows how this works.

[Casey Brooks]

do I still need compose navigation with Ballast navigation

No, Ballast Navigation is an alternative to navigation-compose, and is not compatible with it, nor is it built upon anything from that library. Ballast is a completely separate navigation library which offers a simpler way to do navigation that is not limited to Android or Compose like navigation-compose is. However, since it isn’t tied directly to Compose, it may take a bit more work from you to get some of the nicer features of navigation-compose like transition animations and scoping ViewModels to the NavGraph.

[ayodele]

Thanks for the clarity.

[ubuntudroid]

@Casey Brooks Sorry for digging up this old topic, but I’m struggling with how one would scope a screen ViewModel to the ballast-navigation backstack.

Also, how do I get access to the SavedStateHandle this way? It usually is tied to an Android ViewModel which isn’t what you would use with ballast-navigation if I understand the docs (and the rationale behind them) correctly.

Any hints?