New OnBackEffect

/*

 * Copyright (C) 2023 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 com.android.settingslib.spa.framework.compose

import androidx.activity.OnBackPressedCallback

import androidx.activity.OnBackPressedDispatcher

import androidx.activity.compose.LocalOnBackPressedDispatcherOwner

import androidx.compose.runtime.Composable

import androidx.compose.runtime.DisposableEffect

import androidx.compose.runtime.getValue

import androidx.compose.runtime.remember

import androidx.compose.runtime.rememberUpdatedState

import androidx.compose.ui.platform.LocalLifecycleOwner

/**

 * An effect for detecting presses of the system back button, and the back event will not be

 * consumed by this effect.

 *

 * Calling this in your composable adds the given lambda to the [OnBackPressedDispatcher] of the

 * [LocalOnBackPressedDispatcherOwner].

 *

 * @param onBack the action invoked by pressing the system back

 */

@Composable

fun OnBackEffect(onBack: () -> Unit) {

    val backDispatcher = checkNotNull(LocalOnBackPressedDispatcherOwner.current) {

        "No OnBackPressedDispatcherOwner was provided via LocalOnBackPressedDispatcherOwner"

    }.onBackPressedDispatcher

    // Safely update the current `onBack` lambda when a new one is provided

    val currentOnBack by rememberUpdatedState(onBack)

    // Remember in Composition a back callback that calls the `onBack` lambda

    val backCallback = remember {

        object : OnBackPressedCallback(true) {

            override fun handleOnBackPressed() {

                remove()

                currentOnBack()

                backDispatcher.onBackPressed()

            }

        }

    }

    val lifecycleOwner = LocalLifecycleOwner.current

    DisposableEffect(lifecycleOwner, backDispatcher) {

        // Add callback to the backDispatcher

        backDispatcher.addCallback(lifecycleOwner, backCallback)

        // When the effect leaves the Composition, remove the callback

        onDispose {

            backCallback.remove()

        }

    }

}

/*

 * Copyright (C) 2023 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 com.android.settingslib.spa.framework.compose

import androidx.compose.material3.Text

import androidx.compose.runtime.Composable

import androidx.compose.runtime.CompositionLocalProvider

import androidx.compose.runtime.LaunchedEffect

import androidx.compose.ui.test.hasText

import androidx.compose.ui.test.junit4.createComposeRule

import androidx.navigation.compose.NavHost

import androidx.navigation.compose.composable

import androidx.navigation.compose.rememberNavController

import androidx.test.ext.junit.runners.AndroidJUnit4

import com.android.settingslib.spa.testutils.waitUntilExists

import com.google.common.truth.Truth.assertThat

import kotlinx.coroutines.delay

import org.junit.Rule

import org.junit.Test

import org.junit.runner.RunWith

@RunWith(AndroidJUnit4::class)

class OnBackEffectTest {

    @get:Rule

    val composeTestRule = createComposeRule()

    private var onBackEffectCalled = false

    @Test

    fun onBackEffect() {

        composeTestRule.setContent {

            TestNavHost {

                val navController = LocalNavController.current

                LaunchedEffect(Unit) {

                    navController.navigate(ROUTE_B)

                    delay(100)

                    navController.navigateBack()

                }

            }

        }

        composeTestRule.waitUntilExists(hasText(ROUTE_A))

        assertThat(onBackEffectCalled).isTrue()

    }

    @Composable

    private fun TestNavHost(content: @Composable () -> Unit) {

        val navController = rememberNavController()

        CompositionLocalProvider(navController.localNavController()) {

            NavHost(navController, ROUTE_A) {

                composable(route = ROUTE_A) { Text(ROUTE_A) }

                composable(route = ROUTE_B) {

                    Text(ROUTE_B)

                    OnBackEffect {

                        onBackEffectCalled = true

                    }

                }

            }

            content()

        }

    }

    private companion object {

        const val ROUTE_A = "RouteA"

        const val ROUTE_B = "RouteB"

    }

}