Allow overriding of the default stack index

app/src/main/java/com/tunjid/androidx/MainActivity.kt

@@ -37,6 +37,7 @@ class MainActivity : AppCompatActivity(), GlobalUiHost, Navigator.Controller {
         backStackType = MultiStackNavigator.BackStackType.Unlimited,
         stopInvalidNavigation = true,
         rootFunction = RouteFragment.Companion::newInstance,
+        initialIndex = 0
     )
 
     public override fun onCreate(savedInstanceState: Bundle?) {

app/src/main/java/com/tunjid/androidx/tabnav/navigator/MultipleStacksFragment.kt

@@ -57,6 +57,7 @@ class MultipleStacksFragment : Fragment(R.layout.fragment_multiple_stack) {
         stackCount = DESTINATIONS.size,
         containerId = R.id.inner_container,
         stopInvalidNavigation = true,
+        initialIndex = 0,
         rootFunction = { index ->
             MultipleStackChildFragment.newInstance(getChildName(index), 1)
         }

libraryVersion.properties

@@ -6,7 +6,7 @@ view_version=1.2.0
 material_version=1.0.4
 functions_version=1.0.0
 savedstate_version=1.0.1
-navigation_version=1.2.2
+navigation_version=1.2.3
 recyclerview_version=1.2.0
 viewpager2_version=1.0.0
 communications_version=1.0.0

navigation/src/androidTest/java/com/tunjid/androidx/navigation/MultiStackNavigatorTest.kt

@@ -325,11 +325,26 @@ class MultiStackNavigatorTest {
         }
     }
 
+    @Test
+    fun passingInitialIndexShows() = runBlocking {
+        val multiStackNavigator = multiStackNavigator(MultiStackNavigator.BackStackType.UniqueEntries, initialIndex = 1)
+        assertSame(ROOT_TAG_1, multiStackNavigator.current?.tag)
+    }
+
+    @Test
+    fun noInitialIndexShowsFirstIndex() = runBlocking {
+        val multiStackNavigator = multiStackNavigator(MultiStackNavigator.BackStackType.UniqueEntries, initialIndex = 0)
+        assertSame(ROOT_TAG_0, multiStackNavigator.current?.tag)
+    }
+
     private fun MultiStackNavigator.assertNavigatorIndices(vararg tags: String?) {
         tags.forEachIndexed { index, tag -> assertEquals(tag, navigatorAt(index)?.current?.tag) }
     }
 
-    private fun multiStackNavigator(type: MultiStackNavigator.BackStackType): MultiStackNavigator {
+    private fun multiStackNavigator(
+        type: MultiStackNavigator.BackStackType,
+        initialIndex: Int = 0
+    ): MultiStackNavigator {
         var navigator: MultiStackNavigator? = null
         instrumentation.runOnMainSync {
             navigator = MultiStackNavigator(
@@ -339,6 +354,7 @@ class MultiStackNavigatorTest {
                 backStackType = type,
                 containerId = activity.containerId,
                 stopInvalidNavigation = true,
+                initialIndex = initialIndex
             ) { NavigationTestFragment.newInstance(TAGS[it]) }
         }
 

navigation/src/main/java/com/tunjid/androidx/navigation/MultiStackNavigator.kt

@@ -26,6 +26,7 @@ const val MULTI_STACK_NAVIGATOR = "com.tunjid.androidx.navigation.MultiStackNavi
 fun Fragment.childMultiStackNavigationController(
     stackCount: Int,
     @IdRes containerId: Int,
+    initialIndex: Int,
     backStackType: MultiStackNavigator.BackStackType = MultiStackNavigator.BackStackType.UniqueEntries,
     stopInvalidNavigation: Boolean,
     rootFunction: (Int) -> Fragment,
@@ -34,6 +35,7 @@ fun Fragment.childMultiStackNavigationController(
         stackCount = stackCount,
         stateContainer = savedStateFor(this@childMultiStackNavigationController, "$MULTI_STACK_NAVIGATOR-$containerId"),
         fragmentManager = childFragmentManager,
+        initialIndex = initialIndex,
         containerId = containerId,
         backStackType = backStackType,
         rootFunction = rootFunction,
@@ -44,6 +46,7 @@ fun Fragment.childMultiStackNavigationController(
 fun FragmentActivity.multiStackNavigationController(
     stackCount: Int,
     @IdRes containerId: Int,
+    initialIndex: Int,
     backStackType: MultiStackNavigator.BackStackType = MultiStackNavigator.BackStackType.UniqueEntries,
     stopInvalidNavigation: Boolean,
     rootFunction: (Int) -> Fragment,
@@ -52,6 +55,7 @@ fun FragmentActivity.multiStackNavigationController(
         stackCount = stackCount,
         stateContainer = savedStateFor(this@multiStackNavigationController, "$MULTI_STACK_NAVIGATOR-$containerId"),
         fragmentManager = supportFragmentManager,
+        initialIndex = initialIndex,
         containerId = containerId,
         backStackType = backStackType,
         rootFunction = rootFunction,
@@ -66,6 +70,7 @@ fun FragmentActivity.multiStackNavigationController(
 class MultiStackNavigator(
     stackCount: Int,
     stateContainer: LifecycleSavedStateContainer,
+    private val initialIndex: Int,
     private val fragmentManager: FragmentManager,
     @IdRes override val containerId: Int,
     backStackType: BackStackType = BackStackType.UniqueEntries,
@@ -98,7 +103,11 @@ class MultiStackNavigator(
         }
 
     private val indices = 0 until stackCount
-    internal val stackVisitor = MultiStackVisitor(backStackType, stateContainer)
+    internal val stackVisitor = MultiStackVisitor(
+        backStackType = backStackType,
+        container = stateContainer,
+        initialIndex = initialIndex
+    )
 
     internal val stackFragments: List<StackFragment>
         get() = indices
@@ -300,7 +309,8 @@ class StackFragment : Fragment() {
 
 internal class MultiStackVisitor(
     private val backStackType: MultiStackNavigator.BackStackType,
-    private val container: LifecycleSavedStateContainer
+    private val container: LifecycleSavedStateContainer,
+    private val initialIndex: Int
 ) {
 
     init {
@@ -309,7 +319,7 @@ internal class MultiStackVisitor(
     }
 
     private val delegate = (container.savedState.getIntArray(NAV_STACK_ORDER)
-        ?: intArrayOf(0)).toMutableList()
+        ?: intArrayOf(initialIndex)).toMutableList()
 
     fun visit(value: Int) = delegate.run {
         when (backStackType) {
@@ -333,7 +343,7 @@ internal class MultiStackVisitor(
 
     fun leaveAll(): Unit = delegate.run {
         clear()
-        add(0)
+        add(initialIndex)
         saveState()
     }