我习惯使用 AsyncTask
并且由于它的简单性而很好地理解它。但是Coroutines
让我很困惑。您能否以简单的方式向我解释以下各项的区别和目的是什么?
GlobalScope.launch(Dispatchers.IO) {}
GlobalScope.launch{}
CoroutineScope(Dispatchers.IO).launch{}
lifecycleScope.launch(Dispatchers.IO){}
lifecycleScope.launch{}
最佳答案
首先,让我们从定义开始说清楚。如果您需要 Coroutines 和 Coroutines Flow 的教程或游乐场,您可以查看 tutorial/playground我建立。Scope
是您用来启动协程的对象,它只包含一个对象 CoroutineContext
public interface CoroutineScope {
/**
* The context of this scope.
* Context is encapsulated by the scope and used for implementation of coroutine builders that are extensions on the scope.
* Accessing this property in general code is not recommended for any purposes except accessing the [Job] instance for advanced usages.
*
* By convention, should contain an instance of a [job][Job] to enforce structured concurrency.
*/
public val coroutineContext: CoroutineContext
}
协程上下文是一组规则和配置,它们定义协程将如何执行。
在底层,它是一种映射,具有一组可能的键和值。
协程上下文是不可变的,但您可以使用加号运算符将元素添加到上下文中,
就像您将元素添加到集合中一样,生成一个新的上下文实例
定义协程行为的元素集是:
调度员
调度程序确定应该使用哪个线程池。调度员类也是
协程上下文 可以添加到 CoroutineContext
简而言之 - 任何输入和输出,如名称所述
例如,在 RecyclerView 中显示列表、更新 Views 等。
您可以查看Android's official documents有关调度程序的更多信息。
编辑即使官方文件指出
Dispatchers.IO - This dispatcher is optimized to perform disk or network I/O outside of the main thread. Examples include using the Room component, reading from or writing to files, and running any network operations.
来自 的回答马尔科·托波尔尼克
IO runs the coroutine on a special, flexible thread pool. It exists only as a workaround when you are forced to use a legacy, blocking IO API that would block its calling thread.
也可能是对的。
职位 协程本身由 Job 表示。
Job 是协程的句柄。对于您创建的每个协程(通过启动或异步),
它返回一个唯一标识协程并管理其生命周期的 Job 实例。
您还可以将 Job 传递给 CoroutineScope 以掌握其生命周期。
它负责协程的生命周期、取消和父子关系。
可以从当前协程的上下文中检索当前作业:
Job 可以经历一组状态:New、Active、Completing、Completed、Canceling 和Cancelled。
虽然我们无法访问各州本身,
我们可以访问 Job 的属性:isActive、isCancelled 和 isCompleted。
协程范围 它定义了一个简单的工厂函数,它采用
CoroutineContext
s 作为参数来围绕组合的 CoroutineContext 创建包装器为public fun CoroutineScope(context: CoroutineContext): CoroutineScope =
ContextScope(if (context[Job] != null) context else context + Job())
internal class ContextScope(context: CoroutineContext) : CoroutineScope {
override val coroutineContext: CoroutineContext = context
// CoroutineScope is used intentionally for user-friendly representation
override fun toString(): String = "CoroutineScope(coroutineContext=$coroutineContext)"
}
并创建一个 Job
如果提供上下文还没有一个元素。我们来看一下 GlobalScope 源码
/**
* A global [CoroutineScope] not bound to any job.
*
* Global scope is used to launch top-level coroutines which are operating on the whole application lifetime
* and are not cancelled prematurely.
* Another use of the global scope is operators running in [Dispatchers.Unconfined], which don't have any job associated with them.
*
* Application code usually should use an application-defined [CoroutineScope]. Using
* [async][CoroutineScope.async] or [launch][CoroutineScope.launch]
* on the instance of [GlobalScope] is highly discouraged.
*
* Usage of this interface may look like this:
*
* ```
* fun ReceiveChannel<Int>.sqrt(): ReceiveChannel<Double> = GlobalScope.produce(Dispatchers.Unconfined) {
* for (number in this) {
* send(Math.sqrt(number))
* }
* }
* ```
*/
public object GlobalScope : CoroutineScope {
/**
* Returns [EmptyCoroutineContext].
*/
override val coroutineContext: CoroutineContext
get() = EmptyCoroutineContext
}
如您所见,它扩展了 CoroutineScope
1- GlobalScope.launch(Dispatchers.IO) {}
只要您的应用程序还活着,GlobalScope 就活着,如果您在此范围内进行一些计数并旋转您的设备,它将继续任务/过程。GlobalScope.launch(Dispatchers.IO) {}
只要您的应用程序还活着,但由于使用 Dispatchers.IO
而在 IO 线程中运行,就可以运行2-
GlobalScope.launch{}
它与第一个相同,但默认情况下,如果您没有任何上下文,则启动使用 EmptyCoroutineContext,它使用 Dispatchers.Default,因此唯一的区别是线程与第一个。3-
CoroutineScope(Dispatchers.IO).launch{}
这个和第一个一样,只是语法不同。4-
lifecycleScope.launch(Dispatchers.IO){}
lifecycleScope
是 LifeCycleOwner
的扩展并绑定(bind)到 Activity 或 Fragment 的生命周期,当该 Activity 或 Fragment 被销毁时,范围被取消。/**
* [CoroutineScope] tied to this [LifecycleOwner]'s [Lifecycle].
*
* This scope will be cancelled when the [Lifecycle] is destroyed.
*
* This scope is bound to
* [Dispatchers.Main.immediate][kotlinx.coroutines.MainCoroutineDispatcher.immediate].
*/
val LifecycleOwner.lifecycleScope: LifecycleCoroutineScope
get() = lifecycle.coroutineScope
您也可以将其用作class Activity3CoroutineLifecycle : AppCompatActivity(), CoroutineScope {
private lateinit var job: Job
override val coroutineContext: CoroutineContext
get() = job + Dispatchers.Main + CoroutineName("🙄 Activity Scope") + CoroutineExceptionHandler { coroutineContext, throwable ->
println("🤬 Exception $throwable in context:$coroutineContext")
}
private val dataBinding by lazy {
Activity3CoroutineLifecycleBinding.inflate(layoutInflater)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(dataBinding.root)
job = Job()
dataBinding. button.setOnClickListener {
// This scope lives as long as Application is alive
GlobalScope.launch {
for (i in 0..300) {
println("🤪 Global Progress: $i in thread: ${Thread.currentThread().name}, scope: $this")
delay(300)
}
}
// This scope is canceled whenever this Activity's onDestroy method is called
launch {
for (i in 0..300) {
println("😍 Activity Scope Progress: $i in thread: ${Thread.currentThread().name}, scope: $this")
withContext(Dispatchers.Main) {
dataBinding.tvResult.text = "😍 Activity Scope Progress: $i in thread: ${Thread.currentThread().name}, scope: $this"
}
delay(300)
}
}
}
}
override fun onDestroy() {
super.onDestroy()
job.cancel()
}
}
关于android - GlobalScope 与 CoroutineScope 与生命周期范围,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/65008486/