Android Navigation Component: Start at a different destination than home, programmatically?

问题

I'm trying to implement a multiple navigation controller with multiple back stack BottomNavigationView, as per the github examples. However, the example uses a different nav graph for each tab, which makes things easy. In my case I need to use the same nav graph for all of my tabs, but with different start destinations, than the "home destination" set in the nav graph.

So far I've managed to modify the NavigationExtensions file in order to achieve the single navgraph for all tabs, and I get multiple navControllers with their own back stacks, but I cannot figure out how to start a nav graph at a different destination.

I've tried using .navigate when getting the navcontroller, but since it's not yet attached, it does not work. Any ideas on how to achieve this? Thank you.

回答1:

We had a requirement wherein the displayed start screen would depend if the user has logged on, what we did was the following:

1. Remove app:startDestination on the navigation XML if it exists
2. On your main activity's XML, remove the following fields inside the <fragment> tag: app:defaultNavHost="true" and app:navGraph

3. On our main Activity's onCreate(), we create a NavGraph object :

   NavController navController = Navigation.findNavController(this, R.id.your_nav_hostfragment);    
   NavGraph navGraph = navController.getNavInflater().inflate(R.navigation.your_navigation_xml);
   

4. Then depending on your requirement, you can set the start destination on the NavGraph using setStartDestination, then apply the NavGraph to the NavController:

       if (condition) {
           navGraph.setStartDestination(R.id.screen1);
       } else {
           navGraph.setStartDestination(R.id.screen2);
       }
       navController.setGraph(navGraph);
   

回答2:

I wrote two extensions to do the job. First is to be used to change destination in the current node. The second is to be used to traverse multiple times into nested graphs

_main_graph
 |
 |_nested_graph_1
   |
   |_nested_graph_2  
     |
     |_nested_graph_3
       |
       |_nested_graph_4
         |
         |_change this destination!!!!  

fun NavController.changeNodeDestination(nodeId: Int, destinationId: Int): NavController {
    val graph = graph.findNode(nodeId) as NavGraph
    graph.startDestination = destinationId
    return this
}

fun NavController.changeNodeDestination(vararg nodeIds: Int, destinationId: Int): NavController {
    var currentNode = graph

    nodeIds.forEachIndexed { index, i ->
        currentNode = currentNode.findNode(nodeIds[index]) as NavGraph
    }
    currentNode.startDestination = destinationId
    return this
}

Usage:

        findNavController().changeNodeDestination(
            R.id.navigation_login,
            R.id.nav_change_password,                  // GO two levels inside nested graphs
            destinationId = startDestination
        ).navigate(navID, bundle)

来源：https://stackoverflow.com/questions/56768375/android-navigation-component-start-at-a-different-destination-than-home-progra