等待另一种方法，直到协程完成 [Android Kotlin]

Question

我想让等待方法getCurrentUser或通知该方法，直到协程完成。 因为在协程中初始化的变量conversationKit在方法中使用。 协程在方法integrateConversationKit中启动。这两种方法都在MainActivity的onCreate中调用。 但是我收到错误lateinit property conversationKit has not been initialized。

    class ConversationKitService(private val context: Context) {
       private val scope = CoroutineScope(Dispatchers.Main)
       lateinit var conversationKit: ConversationKit
    
        fun integrateConversationKit() {
        
        
                val job = scope.launch {
                    val result = conversationKitFactory.create(
                        settings = settings
                    )
        
                    when (result) {
        
                        is ConversationKitResult.Success -> conversationKit = result.value
                        is ConversationKitResult.Failure -> println(result.message)
                    }
                }
        
        
            }
        
        
            fun getCurrentUser(): User? {
        
                return conversationKit.getCurrentUser()
            }
    }

Answer 1

您可以使用Flow来响应式更新conversationKit ，然后返回它的第一个非空值

 class ConversationKitService(private val context: Context) {
       private val scope = CoroutineScope(Dispatchers.Main)
       private val conversationKit = MutableStateFlow<ConversationKit?>(null)
    
       fun integrateConversationKit() {
                val job = scope.launch {
                val result = conversationKitFactory.create(
                        settings = settings
                    )
        
                    when (result) {
        
                        is ConversationKitResult.Success -> conversationKit.value = result.value
                        is ConversationKitResult.Failure -> println(result.message)
                    }
                }
        
        
            }
        
        
            suspend fun getCurrentUser() = conversationKit.first{ it != null }.getCurrentUser()
            
    }

Answer 2

我只会让getCurrentUser成为一个挂起调用，从缓存结果的内部挂起调用中获取ConversationKit

   class ConversationKitService(private val context: Context) {
       @Volatile
       private var conversationKit: ConversationKit? = null

       ...

       suspend fun getCurrentUser() = getConversationKit()?.getCurrentUser() 

       private suspend getConversationKit(): ConversationKit? {
           if (conversationKit != null) return conversationKit
           val result = conversationKitFactory.create(settings = settings)
           conversationKit = when (result) {
               is ConversationKitResult.Success -> result.value
               is ConversationKitResult.Failure -> null           
           } 
           return conversationKit
       }          
   }

然后， null值意味着检索该值时出错。 您还可以将其包装在某种Result中，以便返回成功/失败而不是可为空的值。

但是，如果您真正想要做的是使getCurrentUser成为一个不需要协程来使用它的非挂起阻塞调用，那么您可以使用runBlocking ：

   class ConversationKitService(private val context: Context) {
       @Volatile
       private var conversationKit: ConversationKit? = null

       ...

       fun getCurrentUser() = runBlocking { 
           getConversationKit()?.getCurrentUser()
       }

       private suspend getConversationKit(): ConversationKit? {
           if (conversationKit != null) return conversationKit
           val result = conversationKitFactory.create(settings = settings)
           conversationKit = when (result) {
               is ConversationKitResult.Success -> result.value
               is ConversationKitResult.Failure -> null           
           } 
           return conversationKit
       }          
   }

不过，我不会真的推荐这种方法。