如何在做某事之前正确等待 HandlerThread 启动？

Question

在我的项目中，有时创建的线程没有像应该的那样快速启动，这种情况发生在极少数情况下，但大多数情况下会发生在 slow/older 手机上。

我的线程喜欢..

class DBThread(threadName: String) : HandlerThread(threadName) {

private var mWorkerHandler: Handler? = null

    override fun onLooperPrepared() {
        super.onLooperPrepared()
        mWorkerHandler = Handler(looper)
    }

    fun createTask(task: Runnable) {
        mWorkerHandler?.post(task)
    }
}

当我使用它并调用 activity..

//this will handle db queries on background and not on main ui thread
var mDbThread: DBThread = DBThread("dbThread")

//use this to interact to main ui thread from different thread
val mUiHandler = Handler()
var mDb: LocalDatabase? = null

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    mDbThread.start()
    mDb = LocalDatabase.getInstance(this)

    fetchAndSetList()

}

override fun onDestroy() {
    super.onDestroy()

    LocalDatabase.destroyInstance()
    mDbThread.quitSafely()
}


private fun fetchAndSetList(){

    mDbThread.createTask(Runnable {
        val list = getList()
        mUiHandler.post {
            // this sometimes does not trigger
            setList(list)
        }
    })
}

setList 函数有时不会触发。所以我做了这样的事情。

fun createTask(task: Runnable) {
    if(mWorkerHandler == null ){
        createTask(task)
        return
    }
    mWorkerHandler?.post(task)
}

修改后的操作似乎有效，但我不太确定这样做是否安全。提前谢谢你。

Answer 1

我认为mWorkerhandler 为null 的原因是因为Thread.start 将创建新的VMThread 并在VMThread 中启动looper。整个流程是异步的，所以当实际调用 onLooperPrepared 时，为时已晚，因为 "fetchAndSetList" 已经在尝试使用 mWorkerHandler

解决方案是在 HandlerThread 之外创建处理程序：

Handler workerHandler;
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    mDbThread.start()
    workerHandler = new Handler(mDbThread.getLooper());
    mDb = LocalDatabase.getInstance(this)

    fetchAndSetList()
}

private fun fetchAndSetList(){
    workerHandler.post(Runnable {
        val list = getList()
        mUiHandler.post {
            // this sometimes does not trigger
            setList(list)
        }
   })
}

如何在做某事之前正确等待 HandlerThread 启动？

How to properly wait for HandlerThread to start before doing something?

android

android-handlerthread