NavHostController.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 android.content.Context
import android.os.Bundle
import androidx.compose.runtime.Composable
import androidx.compose.runtime.DisposableEffect
import androidx.compose.runtime.MutableState
import androidx.compose.runtime.State
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.saveable.Saver
import androidx.compose.runtime.saveable.rememberSaveable
import androidx.compose.ui.platform.LocalContext
import androidx.navigation.NavBackStackEntry
import androidx.navigation.NavController
import androidx.navigation.NavHostController
/**
* Gets the current navigation back stack entry as a [MutableState]. When the given navController
* changes the back stack due to a [NavController.navigate] or [NavController.popBackStack] this
* will trigger a recompose and return the top entry on the back stack.
*
* @return a mutable state of the current back stack entry
*/
@Composable
public fun NavController.currentBackStackEntryAsState(): State<NavBackStackEntry?> {
val currentNavBackStackEntry = remember { mutableStateOf(currentBackStackEntry) }
// setup the onDestinationChangedListener responsible for detecting when the
// current back stack entry changes
DisposableEffect(this) {
val callback = NavController.OnDestinationChangedListener { controller, _, _ ->
currentNavBackStackEntry.value = controller.currentBackStackEntry
}
addOnDestinationChangedListener(callback)
// remove the navController on dispose (i.e. when the composable is destroyed)
onDispose {
removeOnDestinationChangedListener(callback)
}
}
return currentNavBackStackEntry
}
/**
* Creates a NavHostController that handles the adding of the [ComposeNavigator] and
* [DialogNavigator]. Additional [androidx.navigation.Navigator] instances should be added
* in a [androidx.compose.runtime.SideEffect] block.
*
* @see NavHost
*/
@Composable
public fun rememberNavController(): NavHostController {
val context = LocalContext.current
return rememberSaveable(saver = NavControllerSaver(context)) {
createNavController(context)
}
}
private fun createNavController(context: Context) =
NavHostController(context).apply {
navigatorProvider.addNavigator(ComposeNavigator())
navigatorProvider.addNavigator(DialogNavigator())
}
/**
* Saver to save and restore the NavController across config change and process death.
*/
private fun NavControllerSaver(
context: Context
): Saver<NavHostController, *> = Saver<NavHostController, Bundle>(
save = { it.saveState() },
restore = { createNavController(context).apply { restoreState(it) } }
)