Multiple backstacks instantiated [195668143]

Fixed

Bug

Status Update

No update yet.

Description

pe...@dext.com

created issue #1

Aug 6, 2021 10:36AM

Components used:

Navigation
Compose

Versions used:

Navigation: 2.4.0-alpha04
Compose: 1.0.0

Devices/Android versions reproduced on: Pixel 2

Setup:

The setup can be demonstrated with the following code.

private sealed class BottomBarItem(val route: String) {
  object Landing : BottomBarItem("landing")
  object Settings : BottomBarItem("settings")
}

private val bottomBarItems = listOf(BottomBarItem.Landing, BottomBarItem.Settings)

class MainActivity : ComponentActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContent {
      TestNavigationTheme {
        val navController = rememberNavController()
        NavHost(navController = navController, startDestination = "home") {
          composable("home") { Home { navController.navigate("about") } }
          composable("about") { Text("In About") }
        }
      }
    }
  }
}

@Composable
fun Home(onAboutClick: () -> Unit) {
  val navController = rememberNavController()
  val currentRoute = navController.currentBackStackEntryAsState().value?.destination?.route

  Scaffold(
    bottomBar = {
      BottomNavigation {
        bottomBarItems.forEach { screen ->
          Text(
            text = screen.route,
            color = if (currentRoute == screen.route) Color.Black else Color.White,
            modifier = Modifier.clickable {
              if (currentRoute != screen.route) {
                navController.navigate(screen.route) {
                  popUpTo(navController.graph.startDestinationId)
                  launchSingleTop = true
                }
              }
            }
          )
        }
      }
    }
  ) {
    Box(Modifier.padding(it)) {
      NavHost(navController = navController, startDestination = BottomBarItem.Landing.route) {
        composable(BottomBarItem.Landing.route) { Text(text = "Landing") }
        composable(BottomBarItem.Settings.route) {
          Text(
            text = "Go to about",
            modifier = Modifier.clickable(onClick = onAboutClick)
          )
        }
      }
    }
  }
}

Issue:

Run the following code
Navigate to Settings
Click on Go to about
Click back (effectively go back in Settings)
Repeat 3 & 4 numerous times
Click back to exit the app

Result: We need to click back as many times as we visited the About screen.

Expected result: Only 2 back clicks are needed to close the app:

one to go back to Landing
one to actually close the app

Screen recording: There is an attached demo of the behaviour.

test-navigation-demo.mov

1.4 MB

Download

Comments

il...@google.com <il...@google.com> Sep 14, 2021 11:14PM

Accepted by il...@google.com.

ap...@google.com <ap...@google.com> #2Sep 15, 2021 04:29PM

Project: platform/frameworks/support
Branch: androidx-master-dev

commit c60f33e229e31ab328ef6b59dab63b264954831c
Author: Alexandre Elias <aelias@google.com>
Date: Fri Jul 10 16:23:09 2020

Semantics no-op cleanups

Partly in response to lmr's broad code review, I did a pass of
superficial API/implementation cleanup. The main changes are:

- I changed each Boolean SemanticsProperty where false is equivalent to
not being present to take "Unit" instead. This is conceptually
clearer: it avoids questions like "can I cancel out a semantics from a
merged child by setting it to false?" Because "property = Unit" looks
weird, I also changed the style of these to "property()".

- I moved the Semantics id generator closer to where it's used, in
SemanticsModifierCore. I made it internal and an AtomicInt.
(Note that integer ids are heavily used in the Android
AccessibilityNodeInfo APIs so I can't simply remove them entirely.)

- I deleted dead code. Some examples include SemanticsHintOverrides,
a public API not connected to anything, and SemanticsPropertyKey
merge() open method which is never called. (In both cases I have
a different plan in mind for accessibility.)

Fixes: 145951226
Fixes: 145955412
Test: existing tests
Relnote: "Single-value semantics properties now use a calling style.
For example, 'semantics { hidden = true }' is now written as:
'semantics { hidden() }'."

Change-Id: Ic1afd12ea22c926babc9662f1804d80b33aa0cfc

M ui/integration-tests/benchmark/src/androidTest/java/androidx/ui/benchmark/test/LayoutNodeModifierBenchmark.kt
M ui/ui-core/api/0.1.0-dev15.txt
M ui/ui-core/api/current.txt
M ui/ui-core/api/public_plus_experimental_0.1.0-dev15.txt
M ui/ui-core/api/public_plus_experimental_current.txt
M ui/ui-core/api/restricted_0.1.0-dev15.txt
M ui/ui-core/api/restricted_current.txt
M ui/ui-core/src/androidAndroidTest/kotlin/androidx/ui/graphics/vector/VectorTest.kt
M ui/ui-core/src/androidAndroidTest/kotlin/androidx/ui/semantics/SemanticsTests.kt
M ui/ui-core/src/androidMain/kotlin/androidx/ui/core/AndroidActuals.kt
M ui/ui-core/src/androidMain/kotlin/androidx/ui/core/AndroidComposeView.kt
M ui/ui-core/src/androidMain/kotlin/androidx/ui/core/AndroidComposeViewAccessibilityDelegateCompat.kt
M ui/ui-core/src/androidMain/kotlin/androidx/ui/core/AndroidPopup.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/Expect.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsConfiguration.kt
D ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsHintOverrides.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsModifier.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsNode.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsOwner.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/core/semantics/SemanticsWrapper.kt
M ui/ui-core/src/commonMain/kotlin/androidx/ui/semantics/SemanticsProperties.kt
M ui/ui-foundation/api/0.1.0-dev15.txt
M ui/ui-foundation/api/current.txt
M ui/ui-foundation/api/public_plus_experimental_0.1.0-dev15.txt
M ui/ui-foundation/api/public_plus_experimental_current.txt
M ui/ui-foundation/api/restricted_0.1.0-dev15.txt
M ui/ui-foundation/api/restricted_current.txt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/Clickable.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/Dialog.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/Scroller.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/selection/Selectable.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/selection/Toggleable.kt
M ui/ui-foundation/src/main/java/androidx/ui/foundation/semantics/FoundationSemanticsProperties.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/ButtonTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/CardTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/CheckboxScreenshotTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/RadioButtonScreenshotTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/ScaffoldTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/SnackbarTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/SurfaceTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/ripple/RippleIndicationTest.kt
M ui/ui-material/src/androidTest/java/androidx/ui/material/textfield/TextFieldScreenshotTest.kt
M ui/ui-material/src/main/java/androidx/ui/material/AppBar.kt
M ui/ui-material/src/main/java/androidx/ui/material/TextFieldImpl.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/AssertsTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/CallSemanticsActionTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/ErrorMessagesTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/FindersTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/PrintToStringTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/ScrollToTest.kt
M ui/ui-test/src/androidTest/java/androidx/ui/test/TextActionsTest.kt
M ui/ui-test/src/main/java/androidx/ui/test/Actions.kt
M ui/ui-test/src/main/java/androidx/ui/test/Filters.kt
M ui/ui-text/api/0.1.0-dev15.txt
M ui/ui-text/api/current.txt
M ui/ui-text/api/public_plus_experimental_0.1.0-dev15.txt
M ui/ui-text/api/public_plus_experimental_current.txt
M ui/ui-text/api/restricted_0.1.0-dev15.txt
M ui/ui-text/api/restricted_current.txt
M ui/ui-text/src/commonMain/kotlin/androidx/ui/text/CoreTextField.kt
M ui/ui-text/src/commonMain/kotlin/androidx/ui/text/TextSemanticsProperties.kt

https://android-review.googlesource.com/1360099

il...@google.com <il...@google.com> #3Sep 15, 2021 11:23PM

Marked as fixed.

Generally, this isn't the code you should be writing at all: you should strive for using a single NavHost and using your NavController as the source of truth to show/hide global navigation like your bottom navigation bar using APIs like AnimatedVisibility to transition those components as your route changes:

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            ComposeTestTheme {
                val navController = rememberNavController()
                val currentDestination by navController.currentBackStackEntryAsState()
                Scaffold(
                    bottomBar = {
                        val inMainGraph = currentDestination?.destination?.hierarchy?.any { it.route == "main" } ?: true
                        AnimatedVisibility(
                            visible = inMainGraph,
                            enter = fadeIn() + expandIn(Alignment.BottomCenter),
                            exit = fadeOut() + shrinkOut(Alignment.BottomCenter)
                        ) {
                            BottomNavigation {
                                bottomBarItems.forEach { screen ->
                                    Text(
                                        text = screen.route,
                                        color = if (currentDestination?.destination?.route == screen.route) Color.Black else Color.White,
                                        modifier = Modifier.clickable {
                                            val currentRoute = currentDestination?.destination?.route
                                            if (currentRoute != screen.route) {
                                                navController.navigate(screen.route) {
                                                    popUpTo(navController.graph.findStartDestination().id)
                                                    launchSingleTop = true
                                                }
                                            }
                                        }
                                    )
                                }
                            }
                        }
                    }
                ) {
                    NavHost(navController = navController, startDestination = "main",
                        modifier = Modifier.padding(it)
                    ) {
                        navigation(startDestination = BottomBarItem.Landing.route, route = "main") {
                            composable(BottomBarItem.Landing.route) { Text(text = "Landing") }
                            composable(BottomBarItem.Settings.route) {
                                Settings { navController.navigate("about") }
                            }
                        }
                        composable("about") { Text("In About") }
                    }
                }
            }
        }
    }
}

By using a single NavHost, you ensure that 1) deep links to all those destinations work correctly and 2) you have a single back stack.

That being said, we've fixed this embedded NavHost case for the upcoming Navigation 2.4.0-alpha10.

Issue 195668143

Description

Issue summary

Comments

il...@google.com <il...@google.com> Sep 14, 2021 11:14PM

ap...@google.com <ap...@google.com> #2Sep 15, 2021 04:29PM

il...@google.com <il...@google.com> #3Sep 15, 2021 11:23PM

Add comment

Issue metadata