Retornar um resultado (com base em eventos)

Esta receita demonstra como retornar um resultado de uma tela para uma tela anterior usando uma abordagem baseada em eventos.

Como funciona

Este exemplo usa um ResultEventBus para facilitar a comunicação entre as telas.

  1. ResultEventBusNavEntryDecorator: um NavEntryDecorator que fornece um ResultEventBus via LocalResultEventBus.
  2. ResultEventBus: um ResultEventBus é criado e disponibilizado aos elementos combináveis usando LocalResultEventBus. Esse EventBus envia e recebe os resultados.
  3. Envio do resultado: a tela que produz o resultado chama resultBus.sendResult(person) para enviar os dados de volta como um evento único.
  4. Receber o resultado: a tela que precisa do resultado usa um elemento combinável ResultEffect para detectar resultados de um tipo específico. Quando um resultado é recebido, o lambda do efeito é acionado.

Essa abordagem é útil para resultados temporários que precisam ser tratados como eventos únicos.

/*
 * Copyright 2025 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.example.nav3recipes.results.common

import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.setValue
import androidx.lifecycle.ViewModel

class HomeViewModel : ViewModel() {
    var person by mutableStateOf<Person?>(null)
}
 
/*
 * Copyright 2025 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.example.nav3recipes.results.common

import androidx.navigation3.runtime.NavKey
import kotlinx.serialization.Serializable

@Serializable
data object Home : NavKey

@Serializable
class PersonDetailsForm : NavKey
 
/*
 * Copyright 2025 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.example.nav3recipes.results.common

import android.os.Parcelable
import kotlinx.parcelize.Parcelize

@Parcelize
data class Person(val name: String, val favoriteColor: String) : Parcelable
 
/*
 * Copyright 2025 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.example.nav3recipes.results.common

import androidx.compose.foundation.layout.Spacer
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.text.input.rememberTextFieldState
import androidx.compose.material3.Button
import androidx.compose.material3.OutlinedTextField
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp
import androidx.lifecycle.compose.dropUnlessResumed
import com.example.nav3recipes.content.ContentBlue
import com.example.nav3recipes.content.ContentGreen

@Composable
fun HomeScreen(
    person: Person?,
    onNext: () -> Unit
) {
    ContentBlue("Hello ${person?.name ?: "unknown person"}") {

        if (person != null) {
            Text("Your favorite color is ${person.favoriteColor}")
        }

        Spacer(Modifier.height(16.dp))
        Button(onClick = dropUnlessResumed(block = onNext)) {
            Text("Tell us about yourself")
        }
    }
}

@Composable
fun PersonDetailsScreen(
    onSubmit: (Person) -> Unit
) {
    ContentGreen("About you") {

        val nameTextState = rememberTextFieldState()
        OutlinedTextField(
            state = nameTextState,
            label = { Text("Please enter your name") }
        )

        val favoriteColorTextState = rememberTextFieldState()
        OutlinedTextField(
            state = favoriteColorTextState,
            label = { Text("Please enter your favorite color") }
        )

        Button(
            onClick = dropUnlessResumed {
                val person = Person(
                    name = nameTextState.text.toString(),
                    favoriteColor = favoriteColorTextState.text.toString()
                )
                onSubmit(person)
            },
            enabled = nameTextState.text.isNotBlank() &&
                    favoriteColorTextState.text.isNotBlank()
        ) {
            Text("Submit")
        }
    }
}
 
/*
 * Copyright 2025 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.example.nav3recipes.results.event

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.layout.padding
import androidx.compose.material3.Scaffold
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.lifecycle.viewmodel.compose.viewModel
import androidx.navigation3.runtime.entryProvider
import androidx.navigation3.runtime.rememberNavBackStack
import androidx.navigation3.runtime.result.LocalResultEventBus
import androidx.navigation3.runtime.result.ResultEffect
import androidx.navigation3.runtime.result.ResultEventBus
import androidx.navigation3.runtime.result.rememberResultEventBusNavEntryDecorator
import androidx.navigation3.ui.NavDisplay
import com.example.nav3recipes.results.common.Home
import com.example.nav3recipes.results.common.HomeScreen
import com.example.nav3recipes.results.common.HomeViewModel
import com.example.nav3recipes.results.common.Person
import com.example.nav3recipes.results.common.PersonDetailsForm
import com.example.nav3recipes.results.common.PersonDetailsScreen
import com.example.nav3recipes.ui.setEdgeToEdgeConfig

class ResultEventActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        setEdgeToEdgeConfig()
        super.onCreate(savedInstanceState)

        setContent {
            Scaffold { paddingValues ->

                val backStack = rememberNavBackStack(Home)

                NavDisplay(
                    backStack = backStack,
                    modifier = Modifier.padding(paddingValues),
                    onBack = { backStack.removeLastOrNull() },
                    entryDecorators = listOf(rememberResultEventBusNavEntryDecorator()),
                    entryProvider = entryProvider {
                        entry<Home> {
                            val viewModel = viewModel<HomeViewModel>(key = Home.toString())
                            ResultEffect<Person> { person ->
                                viewModel.person = person
                            }

                            val person = viewModel.person
                            HomeScreen(
                                person = person,
                                onNext = { backStack.add(PersonDetailsForm()) }
                            )
                        }
                        entry<PersonDetailsForm> {
                            val resultBus = LocalResultEventBus.current
                            PersonDetailsScreen(
                                onSubmit = { person ->
                                    resultBus.sendResult<Person>(result = person)
                                    backStack.removeLastOrNull()
                                }
                            )
                        }
                    }
                )
            }
        }
    }
}