toast in jetpack compose

mui3

1. scaffold

   import androidx.compose.foundation.layout.fillMaxSize
   import androidx.compose.foundation.layout.padding
   import androidx.compose.foundation.layout.wrapContentSize
   import androidx.compose.material3.ExtendedFloatingActionButton
   import androidx.compose.material3.Scaffold
   import androidx.compose.material3.SnackbarHost
   import androidx.compose.material3.SnackbarHostState
   import androidx.compose.material3.Text
   import androidx.compose.runtime.mutableStateOf
   import androidx.compose.runtime.remember
   import androidx.compose.runtime.rememberCoroutineScope
   
   val snackbarHostState = remember { SnackbarHostState() }
   val scope = rememberCoroutineScope()
   Scaffold(
       snackbarHost = { SnackbarHost(snackbarHostState) },
       floatingActionButton = {
           var clickCount by remember { mutableStateOf(0) }
           ExtendedFloatingActionButton(
               onClick = {
                   // show snackbar as a suspend function
                   scope.launch {
                       snackbarHostState.showSnackbar(
                           "Snackbar # ${++clickCount}"
                       )
                   }
               }
           ) { Text("Show snackbar") }
       },
       content = { innerPadding ->
           Text(
               text = "Body content",
               modifier = Modifier.padding(innerPadding).fillMaxSize().wrapContentSize()
           )
       }
   )
   

   也可以将显示toast的代码抽离成函数

   fun popupSnackBar(
       scope: CoroutineScope,
       scaffoldState: SnackbarHostState,
       label: String,
       message: String,
       onDismissCallback: () -> Unit = {}
   ) {
       scope.launch {
           scaffoldState.showSnackbar(actionLabel = label, message = message)
           onDismissCallback.invoke()
       }
   }
   

2. viewmodel

   package com.example.modo_demo.ui.page.login
   
   import androidx.compose.runtime.getValue
   import androidx.compose.runtime.mutableStateOf
   import androidx.compose.runtime.setValue
   import androidx.lifecycle.ViewModel
   import androidx.lifecycle.viewModelScope
   import com.example.modo_demo.data.http.ApiCall
   import dagger.hilt.android.lifecycle.HiltViewModel
   import kotlinx.coroutines.channels.Channel
   import kotlinx.coroutines.flow.receiveAsFlow
   import kotlinx.coroutines.launch
   import javax.inject.Inject
   
   class LoginViewModel: ViewModel() {
       var viewStates by mutableStateOf(LoginViewState()) 
       	private set
       private val _viewEvents = Channel<LoginViewEvent>(Channel.BUFFERED)
       val viewEvents = _viewEvents.receiveAsFlow()
       var errorMessage by mutableStateOf("")
       fun login() {
           viewModelScope.launch {
               try {
                   ApiCall.retrofit.login(username = viewStates.username, password = viewStates.password)
               } catch (e: Exception) {
                   errorMessage = e.message.toString()
                   _viewEvents.send(LoginViewEvent.ErrorMessage(errorMessage))
                   e.printStackTrace()
               }
           }
       }
   }
   
   data class LoginViewState(
       val username: String = "",
       val password: String = "",
   )
   
   /**
    * 一次性事件
    */
   sealed class LoginViewEvent {
       object PopBack : LoginViewEvent()
       data class ErrorMessage(val message: String) : LoginViewEvent()
   }
   

3. view

   @OptIn(ExperimentalComposeUiApi::class, InternalCoroutinesApi::class)
   @Composable
   fun LoginPage(
       navCtrl: NavController<Screen>,
       scaffoldState: SnackbarHostState,
       viewModel: LoginViewModel = viewModel()
   ) {
       val viewStates = viewModel.viewStates
       val coroutineState = rememberCoroutineScope()
   
       LaunchedEffect(Unit) {
           viewModel.viewEvents.collect {
               if (it is LoginViewEvent.PopBack) {
                   navCtrl.pop()
               } else if (it is LoginViewEvent.ErrorMessage) {
                   popupSnackBar(coroutineState, scaffoldState, label = SNACK_ERROR, it.message)
               }
           }
       }
       
       Button(
           onClick = {
               keyboardController?.hide()
               viewModel.login()
           },
           modifier = Modifier.padding(horizontal = 20.dp)
       ) {
   
           Text(text = "登录")
       }
   }
   

   在LaunchedEffect中通过event的collect方法来match显示toast的函数