Java 异步任务在Kotlin中的使用

我对Kotlin中的AsyncTask有一个问题，我实际上是新手，所以请冷静：）

这里的问题是，我想在另一个类中使用onPostExecute（）中的结果值

让我向您展示我的代码，在我的Provider.kt文件中有一个ProviderAsync（）类（我只是创建了一个要使用的Hashmap数组）：

---

感谢并抱歉我的英语

您可以利用Kotlin的功能性：

class ProviderAsync(private val callback: (things: ArrayList<HashMap<String, Any>>) -> Unit) : AsyncTask<HashMap<String, Any>, Void, ArrayList<HashMap<String, Any>>>() {

    var allThings: ArrayList<HashMap<String, Any>> = arrayListOf()
    override fun doInBackground(vararg params: HashMap<String, Any>): ArrayList<HashMap<String, Any>>? {
        for (i in 0..2000) {
            val thing = hashMapOf("Loc" to "fr", "name" to "class", "Id" to "23", "tuto" to "fr", "price" to 44)
            allThings.add(thing)
        }
        return null
    }

    override fun onPreExecute() {
        super.onPreExecute()
        // ...
    }

    override fun onPostExecute(result: ArrayList<HashMap<String, Any>>) {
        super.onPostExecute(result)

        //callback function to be executed after getting the result
        callback(result)
    }
}

---

截至2020年6月，

AsyncTask

已弃用。这并不意味着该课程将很快被删除，这意味着谷歌建议你转到其他地方。标准

java.util.concurrent

或相反

使用最后一个，我们可以按如下方式实现它：

在

CoroutineScope

上创建通用扩展函数：

 fun <R> CoroutineScope.executeAsyncTask(
         onPreExecute: () -> Unit,
         doInBackground: () -> R,
         onPostExecute: (R) -> Unit
 ) = launch {
     onPreExecute()
     val result = withContext(Dispatchers.IO) { // runs in background thread without blocking the Main Thread
         doInBackground()
     }
     onPostExecute(result)
 } 

在

活动

或

片段

中：

lifecycleScope.executeAsyncTask(onPreExecute = {
    // ... runs in Main Thread
}, doInBackground = {
    // ... runs in Worker(Background) Thread
    "Result" // send data to "onPostExecute"
}, onPostExecute = {
    // runs in Main Thread
    // ... here "it" is the data returned from "doInBackground"
})

要使用

viewModelScope

或

lifecycleScope

将下一行添加到应用程序的build.gradle文件的依赖项中：

implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$LIFECYCLE_VERSION" // for viewModelScope
implementation "androidx.lifecycle:lifecycle-runtime-ktx:$LIFECYCLE_VERSION" // for lifecycleScope

在编写

final LIFECYCLE\u VERSION=“2.3.0-alpha05”

---

首先，让我知道为什么您不在想要使用返回值的同一个类中编写异步任务？这是我的体系结构，我希望我的提供程序执行异步任务并将数据发送给我的ManagerRefer。您为什么使用

HashMap

而不是

类

？

 fun <R> CoroutineScope.executeAsyncTask(
         onPreExecute: () -> Unit,
         doInBackground: () -> R,
         onPostExecute: (R) -> Unit
 ) = launch {
     onPreExecute()
     val result = withContext(Dispatchers.IO) { // runs in background thread without blocking the Main Thread
         doInBackground()
     }
     onPostExecute(result)
 } 

class MyViewModel : ViewModel() {

    fun someFun() {
        viewModelScope.executeAsyncTask(onPreExecute = {
            // ... runs in Main Thread
        }, doInBackground = {
            // ... runs in Worker(Background) Thread
            "Result" // send data to "onPostExecute"
        }, onPostExecute = {
            // runs in Main Thread
            // ... here "it" is the data returned from "doInBackground"
        })
    }
}

lifecycleScope.executeAsyncTask(onPreExecute = {
    // ... runs in Main Thread
}, doInBackground = {
    // ... runs in Worker(Background) Thread
    "Result" // send data to "onPostExecute"
}, onPostExecute = {
    // runs in Main Thread
    // ... here "it" is the data returned from "doInBackground"
})

implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$LIFECYCLE_VERSION" // for viewModelScope
implementation "androidx.lifecycle:lifecycle-runtime-ktx:$LIFECYCLE_VERSION" // for lifecycleScope