如何等待协程 Dispatch.IO 数据库查询完成以填充 RecyclerView

Question

I'm rewriting my Java note taking app in Kotlin. I'm trying to populate a RecyclerView with TextViews built from my SQLite database query, but I can't figure out how to make it wait for the query to be done, or take an action when it is done.

In my Java version I accomplished this by using AsyncTask for the query and then calling PostExecute.

Now in my Kotlin version I'm using launch(Dispatchers.IO), but I'm not sure how to do the rest. How do I accomplish the same functionality?

Answer 1

In coroutines you can make a queue of non-identical coroutine codes. For example one block from coroutine1 and another one from coroutine2 and make them run sequentially. It is possible using withContext(CoroutineContext)

Assume this code:

fun uiCode() {
  // doing things specially on mainThread
}

fun uiCode2() {
  // More work on mainThread
}

fun ioCode() {
  // Doing something not related to mainThread.
}

fun main() {

  launch(Dispatchers.Main) { // 1- run a coroutine
     uiCode() // will run on MainThread
     withContext(Dispachers.IO) { // 2- Coroutine will wait for ioCode
         ioCode() // Will run on ioThread
     }
     uiCode2() // 3- And then it will run this part
  }
}

If you wanted to do it asyncronously, use launch() , instead of withContext() .