ComposeNavigator.kt
/*
* Copyright 2020 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.navigation.compose
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.setValue
import androidx.navigation.NavBackStackEntry
import androidx.navigation.NavDestination
import androidx.navigation.NavOptions
import androidx.navigation.Navigator
import androidx.navigation.NavigatorState
import androidx.navigation.compose.ComposeNavigator.Destination
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
/**
* Navigator that navigates through [Composable]s. Every destination using this Navigator must
* set a valid [Composable] by setting it directly on an instantiated [Destination] or calling
* [composable].
*/
@Navigator.Name("composable")
public class ComposeNavigator : Navigator<Destination>() {
private var attached by mutableStateOf(false)
/**
* Get the back stack from the [state]. NavHost will compose at least
* once (due to the use of [androidx.compose.runtime.DisposableEffect]) before
* the Navigator is attached, so we specifically return an empty flow if we
* aren't attached yet.
*/
internal val backStack: StateFlow<List<NavBackStackEntry>> get() = if (attached) {
state.backStack
} else {
MutableStateFlow(emptyList())
}
override fun onAttach(state: NavigatorState) {
super.onAttach(state)
attached = true
}
override fun navigate(
entries: List<NavBackStackEntry>,
navOptions: NavOptions?,
navigatorExtras: Extras?
) {
entries.forEach { entry ->
state.add(entry)
}
}
override fun createDestination(): Destination {
return Destination(this) { }
}
override fun popBackStack(popUpTo: NavBackStackEntry, savedState: Boolean) {
state.pop(popUpTo, savedState)
}
/**
* NavDestination specific to [ComposeNavigator]
*/
@NavDestination.ClassType(Composable::class)
public class Destination(
navigator: ComposeNavigator,
internal val content: @Composable (NavBackStackEntry) -> Unit
) : NavDestination(navigator)
internal companion object {
internal const val NAME = "composable"
}
}