I'm experimenting with the Navigation Component an...

# android

[Tudor Luca]

I'm experimenting with the Navigation Component and I'm trying to figure out what's the proper/intended api usage.

Imagine I'm building a Slack clone with the following nav graph:

WorkspacesListFragment                     WorkspaceFragment                    ThreadFragment
            R.id.workspacesListFr                      R.id.workspaceFr                     R.id.threadFr
            +--------------------+                    +-----------------+                 +----------------+
            |                    |                    |                 |                 |                |
            |  List:             |  arg: workspaceId  |  List:          |  arg: threadId  |                |
            |  * kotlinlang      +-------------------->  * androidx     +----------------->                |
 start dest |  * workflow-kotlin |                    |  * compose      |                 |                |
+----------->  * etc...          |                    |  * etc...       |                 |                |
            |                    |                    |                 |                 |                |
            |                    |                    |                 |                 |                |
            |                    |                    |                 |                 |                |
            +------+-------------+                    +-----------------+                 +----------------+
                   |
                   |
                   |
                   |
                   |          CreateWorkspaceFragment
                   |
                   |        +--------------------------+
                   |        |                          |
                   |        | besides a new workspace, |
                   |        | optionally could create  |
                   +--------> a new thread as well     |
                            |                          |
                            |   has workspaceId        |
                            |   has threadId?          |
                            |                          |
                            |                          |
                            |                          |
                            +--------------------------+

When a new workspace is created I'd like to navigate to it when the operation is successful. I've come up with 2 ideas:

Option 1: use the navigation controller available inside CreateWorkspaceFragment and navigate directly from there:

CreateWorkspaceFragment {
    ...
    fun onComplete(workspaceId: String, threadId: String?) {
        val navController = findNavController()
        // 1. Go back to WorkspacesListFragment
        // fragment will trigger an async api call to fetch and then display the list
        navController.popBackStack()

        // 2. Go to WorkspaceFragment
        // fragment will trigger an async api call to fetch and then display the workspace
        navController.navigate(
            WorkspacesListFragmentDirections.actionToWorkspace(workspaceId)
        )

        // 3. Go to ThreadFragment if user created a thread
        // fragment will trigger an async api call to fetch and then display the thread
        if (threadId.isNullOrEmpty().not()){
            navController.navigate(
                WorkspaceFragmentDirections.actionToThread(threadId!!)
            )
        }
    }
}

Option 2:
• return workspaceId & threadId as a result to the previous WorkspacesListFragment Destination (either FragmentResult API or navController.previousBackStackEntry?.savedStateHandle )
• from WorkspacesListFragment I can navigate to WorkspaceFragment and pass along workspaceId & threadId
• inside WorkspaceFragment.onCreate I can check the args and if there's a threadId I'll trigger navigation from there to ThreadFragment (but I'll have to WorkspaceFragment.arguments = null, otherwise when coming back it'll navigate to ThreadFragment again, indefinitely)
Essentially, Option 1 come down to handling my navigation logic in-place and Option 2 would spread it across each destination. FragmentNavigator does Fragment transactions asynchronously, Option 1 acts like navigation is a synchronous operation and it doesn't seem right to me... but Option 2 is a lot more code, so...

Suggestions? (anyone from the androidx.navigation team around here?)

[Ian Lake]

navigate() is a synchronous operation (even if the fragment operations aren't), so just call navigate() and popBackStack() as you want. That's exactly how deep linking works FWIW

[Ian Lake]

Although you probably want your action to use popUpTo to pop your create fragment on the way to the destination instead of manually calling popBackStack() as that will avoid a dispatch to any OnDestinationChangedListener and make it a single atomic operation

[Tudor Luca]

I don't see an obvious way to have a single atomic operation from Create straight to Workspace or Thread? (I'd like to have the backstack populated as I travel from Create to Thread, so going back from Thread would be just popping destinations)

[Ian Lake]

Did you have a question about popUpTo that the docs don't cover? https://developer.android.com/guide/navigation/navigation-navigate#pop

[Ian Lake]

If your back stack is WorkspacesListFragment -> CreateWorkspaceFragment and want to be at a back stack of WorkspacesListFragment -> WorkspaceFragment, then you want to popUpTo CreateWorkspaceFragment with popUpToInclusive="true" and a destination of WorkspaceFragment

[Ian Lake]

While you can use popUpTo to pop multiple destinations before you navigate to your new destination, you can only add one destination to the back stack at a time, so if you wanted to go all the way to ThreadFragment, you'd have to do a separate navigate() afterward with WorkspaceFragmentDirections.actionToThread() as you are doing, yes.

[Tudor Luca]

currently I don't have an action from CreateWorkspaceFragment to WorkspacesListFragment. I'm going back to WorkspacesListFragment by popping Create. does it make a difference if I add an action from CreateWorkspacesFragment to WorkspacesListFragment and popUpTo to pop Create?

[Ian Lake]

that will avoid a dispatch to any OnDestinationChangedListener and make it a single atomic operation

[Ian Lake]

Personally, I'd definitely add the action there, just to make it entirely clear on where you go after the CreateWorkspaceFragment

[Tudor Luca]

but I'll still have 3 .navigate() calls if I want to reach Thread from Create, right?

// 1. Go back to WorkspacesListFragment
navController.navigate(
    CreateWorkspaceFragmentDirections.actionBackToWorkspaceList()
)
// 2. Go to WorkspaceFragment
navController.navigate(
    WorkspacesListFragmentDirections.actionToWorkspace(workspaceId)
)
// 3. Go to ThreadFragment
navController.navigate(
    WorkspaceFragmentDirections.actionToThread(threadId!!)
)

[Ian Lake]

Just two, since you can popUpTo as part of the move to the WorkspaceFragment:

// 1. Go to WorkspaceFragment, popping create on the way out by adding a popUpTo to this action
navController.navigate(
    CreateWorkspaceFragmentDirections.actionToWorkspace(workspaceId)
)
// 2. Go to ThreadFragment
navController.navigate(
    WorkspaceFragmentDirections.actionToThread(threadId!!)
)

[Tudor Luca]

oh right. the action would have the destination set to WorkspaceFragment, not WorkspacesListFragment

[Tudor Luca]

@Ian Lake managed to get something going. thanks so much for your help and very quick responses! 🍻