My team raised me a question regarding compose nav...

# compose

[allan.conda]

My team raised me a question regarding compose navigation and deeplinks which I was not able to answer.
Let’s say we have 2 independent feature modules, A and B.
a screen from A can navigate to a screen from B.
I call the nav graph of B from the top-level module so it has access to the B’s Screen composables, without having A depend directly on B.

We would like a deep link navigation to B with a simulated backstack as if B was opened from a screen in A.
Is this possible with this kind of setup?

[allan.conda]

While writing this question I had the idea of doing two navigation calls something like

navController.navigate("screen_in_A")
navController.navigate("screen_in_B")

Will this work?
Edit: 🤦 forgot we’re talking deeplinks here, so this idea is stupid

[Ian Lake]

The synthetic back stack you get when deep linking is built from the start destination(s) of your graphs, as per the docs: https://developer.android.com/guide/navigation/navigation-deep-link#implicit

[Ian Lake]

So if A is the start destination of your graph, it will be on the back stack

[allan.conda]

Yes, it’s easy when working in a single module since I could do

navigation("main") {
  composable("top") { TopScreen() }

  navigation("A") {
    composable("screen_in_a") { ScreenInA() }

    navigation("B") {
       composable("screen_in_b) {
          ScreenInB()
       }
    }
  }
}

If I understand this correctly.

[allan.conda]

B got complex so we separated it out on its own feature module.
Now the graph looks like

navigation("main") {
  composable("top") { TopScreen() }

  navigationA() // defined in feature_a module
  
  navigationB() // defined in feature_b module
}

so from within A we can still call navController.navigate("screen_in_b") without coupling module A with B

[allan.conda]

Maybe I could hoist the actual composable like this…

navigation("main") {
  navigationA(
      screenInB = {
          ActualScreenInB()
      }
  )
}

// feature a
fun NavGraphBuilder.navigationA(
  screenInB: () -> Unit,
) {
  navigation("A") {
     composable("screen_in_a") { ScreenInA()
     navigation("B") {
       screenInB()
     }
  }
}

[Ian Lake]

Why wouldn't your navigationA() just take a embeddedGraph: NavGraphBuilder.() -> Unit? Then you could do navigationA(navigationB())

[Ian Lake]

If navigation("B") really is a subgraph of navigation("A"), then your graph structure should represent that

[allan.conda]

Wow…

[allan.conda]

I simply didn’t think of that 😓

then your graph structure should represent that

Yeah! I was thinking of this too, having two nav graphs at the same level doesn’t seem right, I use that kind of pattern more for global/shared navigations.
I just never thought I could just pass the graph directly…

Thanks Ian!