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/*
* 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
*
* https://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 com.example.owl.ui.utils
import android.os.Parcelable
import androidx.activity.OnBackPressedCallback
import androidx.activity.OnBackPressedDispatcher
import androidx.compose.runtime.Composable
import androidx.compose.runtime.onCommit
import androidx.compose.runtime.remember
import androidx.compose.runtime.savedinstancestate.listSaver
import androidx.compose.runtime.staticAmbientOf
import androidx.compose.runtime.toMutableStateList
/**
* A simple navigator which maintains a back stack.
*/
class Navigator<T : Parcelable> private constructor(
initialBackStack: List<T>,
backDispatcher: OnBackPressedDispatcher
) {
constructor(
initial: T,
backDispatcher: OnBackPressedDispatcher
) : this(listOf(initial), backDispatcher)
private val backStack = initialBackStack.toMutableStateList()
private val backCallback = object : OnBackPressedCallback(canGoBack()) {
override fun handleOnBackPressed() {
back()
}
}.also { callback ->
backDispatcher.addCallback(callback)
}
val current: T get() = backStack.last()
fun back() {
backStack.removeAt(backStack.lastIndex)
backCallback.isEnabled = canGoBack()
}
fun navigate(destination: T) {
backStack += destination
backCallback.isEnabled = canGoBack()
}
private fun canGoBack(): Boolean = backStack.size > 1
companion object {
/**
* Serialize the back stack to save to instance state.
*/
fun <T : Parcelable> saver(backDispatcher: OnBackPressedDispatcher) =
listSaver<Navigator<T>, T>(
save = { navigator -> navigator.backStack.toList() },
restore = { backstack -> Navigator(backstack, backDispatcher) }
)
}
}
/**
* An effect for handling presses of the device back button.
*/
@Composable
fun backHandler(
enabled: Boolean = true,
onBack: () -> Unit
) {
val backCallback = remember(onBack) {
object : OnBackPressedCallback(enabled) {
override fun handleOnBackPressed() {
onBack()
}
}
}
onCommit(enabled) {
backCallback.isEnabled = enabled
}
val dispatcher = BackDispatcherAmbient.current
onCommit(backCallback) {
dispatcher.addCallback(backCallback)
onDispose {
backCallback.remove()
}
}
}
/**
* An [androidx.compose.runtime.Ambient] providing the current [OnBackPressedDispatcher]. You must
* [provide][androidx.compose.runtime.Providers] a value before use.
*/
internal val BackDispatcherAmbient = staticAmbientOf<OnBackPressedDispatcher> {
error("No Back Dispatcher provided")
}