[英]How to emit data from an asycnhronous callback using Kotlin Flow?
I'm starting to learn Kotlin Flow and Coroutines but I do not know how to make the code below works.我开始学习 Kotlin Flow 和 Coroutines,但我不知道如何使下面的代码工作。 What am I doing wrong?
我究竟做错了什么?
interface MessagesListener {
fun onNewMessageReceived(message: String)
}
fun messages(): Flow<String> = flow {
val messagesListener = object : MessagesListener {
override fun onNewMessageReceived(message: String) {
// The line below generates the error 'Suspension functions can be called only within coroutine body'
emit(message)
}
}
val messagesPublisher = MessagesPublisher(messagesListener)
messagesPublisher.connect()
}
I believe you should be able to use callbackFlow
....something like:我相信你应该能够使用
callbackFlow
....类似:
fun messages(): Flow<String> = callbackFlow {
val messagesListener = object : MessagesListener {
override fun onNewMessageReceived(message: String) {
trySend(message)
}
}
val messagesPublisher = MessagesPublisher(messagesListener)
messagesPublisher.connect()
}
What you are trying to achieve is not possible because emit
is a suspend
function.您试图实现的目标是不可能的,因为
emit
是一个suspend
函数。
However, you can use callbackFlow which is designed for such cases to convert Listeners/Callbacks into Coroutine's Flows.但是,您可以使用专为此类情况设计的callbackFlow将 Listeners/Callbacks 转换为 Coroutine 的 Flows。
fun messages() = callbackFlow<String> {
val messagesListener = object : MessagesListener {
override fun onNewMessageReceived(message: String) {
trySend(message)
}
}
val messagesPublisher = MessagesPublisher(messagesListener)
messagesPublisher.connect()
}
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