带有协程的嵌套回调函数

Question

我想使用 kotlin 协同程序从 javascript 风格的回调函数 async/await 获得响应。

这是我的回调函数

offlineCatalog.findOfflineVideoById(id, object : OfflineCallback<Video> {
     override fun onSuccess(video: Video?) {
         video?.let { 
              //Return This Video
         } ?: kotlin.run { 
              findVideoOnline(id, state) 
         }
    }
    override fun onFailure(throwable: Throwable?) {
         findVideoOnline(id, state)
    }
})

onlineCatalog.findVideoByID(id, object : VideoListener() {
    override fun onVideo(video: Video?) {
         video?.let { 
             //Return This Video 
         } ?: kotlin.run { 
            Log.e("Return Error") 
         }
    }
    override fun onError(errors: MutableList<CatalogError>) {
         super.onError(errors)
         Log.e("Return Error")
    }
})

如果 OfflineCatalog 出错，我想调用 return 来自 OfflineCatalog 视频对象的函数，然后从 OnlineCatalog.

搜索

比如

 try{
     val video:Video? = getVideo(id:String)
     //do something 
 }catch(throwable:Throwable){
     Log.e("Video not found")
 }

更新：我的实现n

这是我想出来的

suspend fun getVideo(id: String): Video? = withContext(Dispatchers.IO) {
    var video = getVideoOffline(id)
    video?.let { video } ?: kotlin.run { getVideoOnline(id) }
}

suspend fun getVideoOffline(id: String): Video? = suspendCancellableCoroutine { cont ->
    (offlineCatalog.findOfflineVideoById(id, object : OfflineCallback<Video> {
        override fun onSuccess(video: Video?) = cont.resume(video)
        override fun onFailure(throwable: Throwable?) = cont.resume(null)
    }))
}

suspend fun getVideoOnline(id: String): Video? = suspendCancellableCoroutine { cont ->
    catalog.findVideoByID(id, object : VideoListener() {
        override fun onVideo(video: Video?) = cont.resume(video)
        override fun onError(errors: MutableList<CatalogError>) = cont.resume(null)
    })
}

用法-

CoroutineScope(Dispatchers.Main).launch {
    getVideo(id)?.let { 
        //Do Something
    } ?: kotlin.run{
        //Video Not Found
    }
}

Answer 1

你必须这样做

@ExperimentalCoroutinesApi
suspend fun getVideo(id: String): Video? = coroutineScope {
    val offlineVideo: Video? = suspendCancellableCoroutine { cont ->
        offlineCatalog.findOfflineVideoById(id, object : OfflineCallback<Video> {
            override fun onSuccess(video: Video?) {
                cont.resume(video)
            }
            override fun onFailure(throwable: Throwable?) {
                cont.resume(null)
            }
        })
    }
    offlineVideo ?: suspendCancellableCoroutine { cont ->
        // offlineVideo not found so search from onlineCatalog
        onlineCatalog.findVideoByID(id, object : VideoListener() {
            override fun onVideo(video: Video?) {
                cont.resume(video)
            }

            override fun onError(errors: MutableList<CatalogError>) {
                super.onError(errors)
                cont.resumeWithException(someException)
            }
        })
    }
}

然后你就可以随便调用了

someScope.launch {
    try {
        val video: Video? = getVideo(id)
        //do something
    } catch (throwable: Throwable) {
        Log.e("Video not found")
    }
}

阅读更多关于 suspendCancellableCoroutine here

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