Kotlin -- 异步操作

概述

在使用 Java 处理异步操作，比如网络请求后更新UI展示，我们首选的是 RxJava，那么转到 Kotlin 上面，我们可以使用协程来替代 RxJava 进行异步操作。

使用 Coroutines 代替 RxJava

interface GankService {
    @GET("data/category/GanHuo/type/{category}/page/{page}/count/{pageCount}")
    fun getGankData(
        @Path("category") category: String, @Path("pageCount") pageCount: Int, @Path("page") page: Int
    ): Call<GankDataResponse>
}

fun getGankData(category:String, pageCount:Int, page:Int, onSuccess:(reponse:GankDataResponse) -> Unit = {}, onFail: () -> Unit ={}){
    GlobalScope.launch(Dispatchers.IO) {
        val reponse = service.getGankData(category, pageCount, page).execute()
        withContext(Dispatchers.Main) {
            if (reponse.isSuccessful) {
                onSuccess(reponse.body() as GankDataResponse)
            }else{
                onFail()
            }
        }
    }
}

还可以这样写：

fun getGankData(category:String, pageCount:Int, page:Int, onSuccess:(reponse:GankDataResponse) -> Unit = {}, onFail: () -> Unit ={}){
    GlobalScope.launch(Dispatchers.Main) {
        val reponse = withContext(Dispatchers.IO) {
            service.getGankData(category, pageCount, page).execute()
        }

        if (reponse.isSuccessful) {
            onSuccess(reponse.body() as GankDataResponse)
        }else{
            onFail()
        }
    }
}

override fun loadData(type: String) {
    RequestManager.instance.getGankData(type, 20, 1,
        onSuccess = {gankDataResponse: GankDataResponse ->
            mView.setRefreshing(false)
            val list = ArrayList<GankItem>()
            if (gankDataResponse != null && gankDataResponse.data != null) {
                for (bean in gankDataResponse.data) {
                    list.add(GankContentItem(bean))
                }
            }
            mView.updateData(list)
            mView.updateSuccess(list.isEmpty())
        },


        onFail =  {
            mView.setRefreshing(false)
            mView.updateError()
        }

    )
}

线程切换

比如，有这样的使用场景，我们查询数据库，然后更新 UI，然后通过网络请求数据，最后再在 UI 上面进行展示，因为数据库和网络请求都是耗时操作，我们要在后台线程执行这样的操作，两次的 UI 展示要在主线程进行操作，这样就涉及到多次线程之间的切换，我们可以通过下面的代码示例解决：

fun httpGet() = GlobalScope.async(Dispatchers.IO){
    delay(100)
    Log.e("Test","httpGet")
    "httpGet return"
}
fun queryDB()  = GlobalScope.async(Dispatchers.IO){
    delay(100)
    Log.e("Test","queryDB")
    "queryDB return"
}

fun updateUI1(p:String)  = GlobalScope.async(Dispatchers.Main){
    Log.e("Test","updateUI1 $p")
}

fun updateUI2(p:String)  = GlobalScope.async(Dispatchers.Main){
    Log.e("Test","updateUI2 $p")
}

GlobalScope.launch(Dispatchers.IO) {
    val ret1 = queryDB().await()
    Log.e("Test",ret1)
    updateUI1(ret1)
    val ret2 = httpGet().await()
    Log.e("Test",ret2)
    updateUI2(ret2)
    Log.e("Test","GlobalScope.launch")
}
Log.e("Test","end")