如何从非挂起回调函数中从 LiveData 构建器发出

Question

我是 LiveData 和 Kotlin 协程的新手。我正在尝试使用 Chromium Cronet library to make a request from my repository class to return a LiveData object. To return the liveData, I'm using the new LiveData builder (coroutines with LiveData)。我将如何发出成功的 Cronet 请求的结果？

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

解决方案涉及将 UrlRequest.Callback 传统回调结构包装在 suspendCoroutine 构建器中。

我也在 Medium article which discusses Cronet integration with LiveData and Kotlin Coroutines.

中记录了我的学习

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)
}

如何从非挂起回调函数中从 LiveData 构建器发出

How to emit from a LiveData builder from a non-suspending callback function

coroutine

kotlin

cronet

android-livedata

kotlin-coroutines