Android开发Kotlin语言协程的依赖及使用示例

//协程依赖
 implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.4"
 implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.6.4"

//开启协程
    fun runCoroutine() {
        Log.i("SecondActivity", "协程开始执行")
        Log.i("SecondActivity", "thread=${Thread.currentThread().name}")
        CoroutineScope(Dispatchers.IO).launch {
            delay(2000)
            Log.i("SecondActivity", "协程内部")
            Log.i("SecondActivity", "thread11=${Thread.currentThread().name}")

        }
        Log.i("SecondActivity", "协程下面")
    }

结果：
协程开始执行
thread=main
协程下面
协程内部
thread11=DefaultDispatcher-worker-1

@Suppress("FunctionName")
public fun CoroutineScope(context: CoroutineContext): CoroutineScope =
    ContextScope(if (context[Job] != null) context else context + Job())

public suspend fun <T> withContext(
    context: CoroutineContext,
    block: suspend CoroutineScope.() -> T
): T {
}

public fun CoroutineScope.launch(
    context: CoroutineContext = EmptyCoroutineContext,
    start: CoroutineStart = CoroutineStart.DEFAULT,
    block: suspend CoroutineScope.() -> Unit
): Job {
    val newContext = newCoroutineContext(context)
    val coroutine = if (start.isLazy)
        LazyStandaloneCoroutine(newContext, block) else
        StandaloneCoroutine(newContext, active = true)
    coroutine.start(start, coroutine, block)
    return coroutine
}

val apiService by lazy { RetrofitClient.instance.create() }
  //开启协程
    fun runCoroutine(name: String, password: String, resultListener: (String, String) -> Unit) {
        Log.i("SecondActivity", "协程开始执行")
        Log.i("SecondActivity", "thread=${Thread.currentThread().name}")
        CoroutineScope(Dispatchers.IO).launch {
            Log.i("SecondActivity", "协程内部")
            Log.i("SecondActivity", "thread11=${Thread.currentThread().name}")
            val request = HttpAccountLoginRequest(name, password, null)
            val block :suspend CoroutineScope.()->BaseResult<HttpAccountLoginResponse> ={
                apiService.requestAccountLogin(request,"android","3.5.4")
            }
            var result:BaseResult<HttpAccountLoginResponse> =block()
            if (result.code=="200"&&result.datas!=null){
                withContext(Dispatchers.Main){
                }
            }
        }
        Log.i("SecondActivity", "协程下面")
    }

栗子：
 CoroutineScope(Dispatchers.IO).async {
        }
源码：
public fun <T> CoroutineScope.async(
    context: CoroutineContext = EmptyCoroutineContext,
    start: CoroutineStart = CoroutineStart.DEFAULT,
    block: suspend CoroutineScope.() -> T
): Deferred<T> {
    val newContext = newCoroutineContext(context)
    val coroutine = if (start.isLazy)
        LazyDeferredCoroutine(newContext, block) else
        DeferredCoroutine<T>(newContext, active = true)
    coroutine.start(start, coroutine, block)
    return coroutine
}

栗子：
CoroutineScope(Dispatchers.IO).launch {
}
源码：
public fun CoroutineScope.launch(
    context: CoroutineContext = EmptyCoroutineContext,
    start: CoroutineStart = CoroutineStart.DEFAULT,
    block: suspend CoroutineScope.() -> Unit
): Job {
    val newContext = newCoroutineContext(context)
    val coroutine = if (start.isLazy)
        LazyStandaloneCoroutine(newContext, block) else
        StandaloneCoroutine(newContext, active = true)
    coroutine.start(start, coroutine, block)
    return coroutine
}

//Job 也是继承自 Element，所以它本身也是一个协程上下文 context
public interface Job : CoroutineContext.Element {
    //Key对象，如果你看到 context[Job] 的写法， 就知道其实指的是这里的这个伴生对象 Key
    public companion object Key : CoroutineContext.Key<Job> {
        init {
            CoroutineExceptionHandler
        }
    }
    //是否活动状态，必须满足几个条件：该协程已经启动、没有完成、没有被取消
    public val isActive: Boolean
    //是否完成状态
    public val isCompleted: Boolean
    //是否被取消状态
    public val isCancelled: Boolean   
    //启动协程，开始调度。如果已经启动了，则返回false。与线程的Thread.start()挺类似
    public fun start(): Boolean
    //挂起当前正在运行的协程，等待该 Job 执行完成。与线程的Thread.join()挺类似
    public suspend fun join()
    //取消该 Job
    public fun cancel(cause: CancellationException? = null)
    //该 Job 的子 Job
    public val children: Sequence<Job>
}

var info: String? = null
        println(info?.length)  //第一种补救：如果info为null，就不执行后面的.length代码
        println(info!!.length)  //第二种补救：这里如果为null，我自己负责info，会报出空指针，这种处理需慎用
        if (info != null) {   //第三种补救措施，如下这种同java写法
            println(info.length)
        }
      println(info?.length ?: "空数据")  //第四种补救措施，如果真的为null，则改为返回"空数据"