如何从LiveData构建器从非挂起的回调函数发出

Question

我是LiveData和Kotlin Coroutines的新手。我正试图使用Chromium Cronet库从我的存储库类发出返回LiveData对象的请求。为了返回liveData，我使用了新的liveData构建器(与liveData协同运行(。如何从成功的Cronet请求中发出结果？

class CustomRepository @Inject constructor(private val context: Context, private val gson: Gson) : Repository {
private val coroutineDispatcher = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
override suspend fun getLiveData(): LiveData<List<MyItem>> = liveData(coroutineDispatcher) {
val executor = Executors.newSingleThreadExecutor()
val cronetEngineBuilder = CronetEngine.Builder(context)
val cronetEngine = cronetEngineBuilder.build()
val requestBuilder = cronetEngine.newUrlRequestBuilder(
"http://www.exampleApi.com/example",
CustomRequestCallback(gson),
executor
)
val request: UrlRequest = requestBuilder.build()
request.start()
}
class CustomRequestCallback(private val gson: Gson) : UrlRequest.Callback() {
override fun onReadCompleted(request: UrlRequest?, info: UrlResponseInfo?, byteBuffer: ByteBuffer?) {
byteBuffer?.flip()
byteBuffer?.let {
val byteArray = ByteArray(it.remaining())
it.get(byteArray)
String(byteArray, Charset.forName("UTF-8"))
}.apply {
val myItems = gson.fromJson(this, MyItem::class.java)
// THIS IS WHAT I WANT TO EMIT
// emit(myItems) doesn't work since I'm not in a suspending function
}
byteBuffer?.clear()
request?.read(byteBuffer)
}
// other callbacks not shown
}

}

Answer 1

该解决方案涉及在suspendCoroutine构建器中封装UrlRequest.Callback传统回调结构。

我还在Medium的一篇文章中记录了我的学习，该文章讨论了Cronet与LiveData和Kotlin Coroutines的集成。

override suspend fun getLiveData(): LiveData<List<MyItem>> = liveData(coroutineDispatcher) {
lateinit var result: List<MyItem>
suspendCoroutine<List<MyItem>> { continuation ->
val requestBuilder = cronetEngine.newUrlRequestBuilder(
"http://www.exampleApi.com/example",
object : UrlRequest.Callback() {
// other callbacks not shown
override fun onReadCompleted(request: UrlRequest?, info: UrlResponseInfo?, byteBuffer: ByteBuffer?) {
byteBuffer?.flip()
byteBuffer?.let {
val byteArray = ByteArray(it.remaining())
it.get(byteArray)
String(byteArray, Charset.forName("UTF-8"))
}.apply {
val myItems = gson.fromJson(this, MyItem::class.java)
result = myItems
continuation.resume(result)
}
byteBuffer?.clear()
request?.read(byteBuffer)
},
executor
)
val request: UrlRequest = requestBuilder.build()
request.start()
}
emit(result)
}