IssueTracker

If you have an 'overlay' (like the example above of controlling a drawer that sits semantically above the entire NavHost), you should be adding it to composition only when you want to start handling back (e.g., if (condition) BackHandler {} rather than using the enabled property). That, combined with the position after the NavHost is how you ensure that your callback is the last to register.

Keep in mind that with Predictive Back, by adding any handling of back, you are also responsible for what animations need to run when going back, which means you should only ever be adding a BackHandler when you are controlling part of the UI itself as explained in the callback best practices. That specifically means you should never be using BackHandler to do logging or affect the back stack of something you do not own (e.g., you should never be calling navController.popBackStack() in your own callback).

The PredictiveBackHandler is what gives you the proper progress to implement the Predictive Back gesture.

If you have a drawer in Scaffold in Material2, it doesn't work right.

I'm using androidx.compose.material:material:1.5.4, which is from the latest Compose BOM.

originally I had something like

val coroutineScope = rememberCoroutineScope()
val scaffoldState = rememberScaffoldState()
BackHandler(enabled = scaffoldState.drawerState.isOpen) {
    coroutineScope.launch { scaffoldState.drawerState.close() }
}
Scaffold(
    scaffoldState = scaffoldState,
    drawerContent = {
        AppDrawer()
    },
    content = {
        HomeScreen()
    }
)

but i also tried

val coroutineScope = rememberCoroutineScope()
val scaffoldState = rememberScaffoldState()
Scaffold(
    scaffoldState = scaffoldState,
    drawerContent = {
        BackHandler(true) {
            coroutineScope.launch { scaffoldState.drawerState.close() }
        }
        AppDrawer()
    },
    content = {
        HomeScreen()
    }
)

Here the drawer is in the composition immediately because that is how Scaffold is implemented.

If I navigate to a few screens and then open up the drawer, then the NavHost consumes the back press because it was last added to the composition and the drawer stays open until the backstack size gets to 1.

There's no way to disable this

Re comment#7 - as per comment#6, your BackHandler needs to be after the NavHost, not before it, and should be using an if (scaffoldState.drawerState.isOpen) BackHandler {} pattern rather than using the enabled property for an overlay.

I believe this is still an issue even without using NavHost at all. I filed a new issue here

Is there any development on being able to configure the BackHandler in the NavHost? Our application also has this issue. Below is our navigation architecture:

| HorizontalPager (beyondBoundsPageCount == pages size) <-- This is key
    | Tab 1..4
    | Tab 5
        | NavHost

Because each tab is composed, we have to track the 'active' tab as to enable/disable the tab's respective BackHandler. However, if I am on tab 2 which is an Ionic Portal (web micro-front-end), when using the BackHandler to handle navigation events, the NavHost on tab 5 receives the events if the currentBackStack.size > 1. We cannot move the BackHandler to be after the NavHost as it will make the BackHandler's within each destination route not consumable.

In addition to this, if we move Tab 5 to a higher order position in the HorizontalPager (say position 1 or 2), this issue does not occur. It's only happening when it's the 'last' tab in the pager. We cannot re-order our tab positions as this is a requirement from our Product Manager.

Furthermore, it would be helpful if the BackHandler/PredictiveBackHandler would check the NavController's enableOnBackPressedCallback. Seems like the simplest approach.