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compose-samples/Owl/app/src/main/java/com/example/owl/ui/utils/Navigation.kt
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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") | |
} |