Android协程高级用法大全

远远落后 發表於 2025-8-19 11:30:58

<div id="navCategory"><h5 class="catalogue">目录</h5><ul class="first_class_ul"><li>1️⃣ 协程作用域（CoroutineScope）与生命周期绑定</li><ul class="second_class_ul"><li>Activity/Fragment 中</li><li>手动创建 CoroutineScope</li></ul><li>2️⃣ 异步组合：并发和串行</li><ul class="second_class_ul"><li>串行执行</li><li>并行执行</li><li>并行 + awaitAll</li></ul><li>3️⃣ 异常处理与结构化并发</li><ul class="second_class_ul"><li>try-catch</li><li>CoroutineExceptionHandler</li><li>SupervisorJob</li></ul><li>4️⃣ 切换线程/调度器</li><ul class="second_class_ul"><li>usewithContext替代launch切换线程</li></ul><li>5️⃣ 超时与取消</li><ul class="second_class_ul"><li>超时</li><li>取消</li><li>可取消挂起函数</li></ul><li>6️⃣ Channels 与 Flow（响应式数据流）</li><ul class="second_class_ul"><li>Channel</li><li>Flow</li></ul><li>7️⃣ 高级技巧</li><ul class="second_class_ul"></ul></ul></div><p>这里系统梳理一下 <strong>Android/Kotlin 协程</strong> 的一些高级用法。会从 <strong>上下文管理、作用域控制、异常处理、性能优化、异步组合</strong> 等角度讲解，给你落地可用的示例。</p>
<p class="maodian"></p><h2>1️⃣ 协程作用域（CoroutineScope）与生命周期绑定</h2>
<p>在 Android 中，协程最好绑定到 <strong>生命周期</strong>，避免内存泄漏。</p>
<p class="maodian"></p><h3>Activity/Fragment 中</h3>
<div class="jb51code"><pre class="brush:java;">class MainActivity : AppCompatActivity() {
// 生命周期感知协程作用域
private val scope = lifecycleScope
override fun onCreate(savedInstanceState: Bundle?) {
   super.onCreate(savedInstanceState)
   scope.launch {
         val data = fetchData()
         updateUI(data)
   }
}
}</pre></div>
<ul><li><strong>lifecycleScope</strong>：绑定 Activity/Fragment 生命周期，自动取消</li><li><strong>viewModelScope</strong>：绑定 ViewModel 生命周期</li></ul>
<p class="maodian"></p><h3>手动创建 CoroutineScope</h3>
<div class="jb51code"><pre class="brush:java;">private val customScope = CoroutineScope(Dispatchers.IO + SupervisorJob())</pre></div>
<ul><li>可以用 <code>SupervisorJob()</code> 避免一个子协程失败影响其它子协程</li><li>记得在 <code>onDestroy()</code> 或 <code>onCleared()</code> 时 <code>customScope.cancel()</code></li></ul>
<p class="maodian"></p><h2>2️⃣ 异步组合：并发和串行</h2>
<p class="maodian"></p><h3>串行执行</h3>
<div class="jb51code"><pre class="brush:java;">val result1 = async { fetchData1() }.await()
val result2 = async { fetchData2() }.await()
val finalResult = combine(result1, result2)</pre></div>
<ul><li>按顺序等待，每个任务完成后再执行下一个</li></ul>
<p class="maodian"></p><h3>并行执行</h3>
<div class="jb51code"><pre class="brush:java;">val deferred1 = async { fetchData1() }
val deferred2 = async { fetchData2() }
val result1 = deferred1.await()
val result2 = deferred2.await()</pre></div>
<ul><li>并行启动，节省等待时间</li></ul>
<p class="maodian"></p><h3>并行 + awaitAll</h3>
<div class="jb51code"><pre class="brush:java;">val results = awaitAll(
async { fetchData1() },
async { fetchData2() },
async { fetchData3() }
)</pre></div>
<p class="maodian"></p><h2>3️⃣ 异常处理与结构化并发</h2>
<p class="maodian"></p><h3>try-catch</h3>
<div class="jb51code"><pre class="brush:java;">scope.launch {
try {
   val result = fetchData()
} catch (e: IOException) {
   handleError(e)
}
}</pre></div>
<p class="maodian"></p><h3>CoroutineExceptionHandler</h3>
<div class="jb51code"><pre class="brush:java;">val handler = CoroutineExceptionHandler { _, exception ->
Log.e("Coroutine", "Caught $exception")
}
scope.launch(handler) {
val result = fetchData()
}</pre></div>
<p class="maodian"></p><h3>SupervisorJob</h3>
<ul><li>父协程失败不影响子协程</li></ul>
<div class="jb51code"><pre class="brush:java;">val supervisor = SupervisorJob()
val scope = CoroutineScope(Dispatchers.IO + supervisor)</pre></div>
<p class="maodian"></p><h2>4️⃣ 切换线程/调度器</h2>
<ul><li><strong>Dispatchers.Main</strong> → UI 操作</li><li><strong>Dispatchers.IO</strong> → 网络/文件操作</li><li><strong>Dispatchers.Default</strong> → CPU 密集型计算</li></ul>
<div class="jb51code"><pre class="brush:java;">scope.launch(Dispatchers.IO) {
val data = fetchData()
withContext(Dispatchers.Main) {
   updateUI(data)
}
}</pre></div>
<p class="maodian"></p><h3>usewithContext替代launch切换线程</h3>
<ul><li>便于返回值，避免嵌套 <code>launch</code></li></ul>
<p class="maodian"></p><h2>5️⃣ 超时与取消</h2>
<p class="maodian"></p><h3>超时</h3>
<div class="jb51code"><pre class="brush:java;">try {
withTimeout(3000L) {
   fetchData()
}
} catch (e: TimeoutCancellationException) {
Log.e("Coroutine", "Timeout")
}</pre></div>
<p class="maodian"></p><h3>取消</h3>
<div class="jb51code"><pre class="brush:java;">val job = scope.launch {
fetchData()
}
job.cancel() // 立即取消</pre></div>
<p class="maodian"></p><h3>可取消挂起函数</h3>
<ul><li>网络、延迟、Channel 等挂起函数是可取消的</li><li>CPU 密集型循环需要手动检查 <code>isActive</code>：</li></ul>
<div class="jb51code"><pre class="brush:java;">for (i in 1..1000) {
if (!isActive) break
doWork()
}</pre></div>
<p class="maodian"></p><h2>6️⃣ Channels 与 Flow（响应式数据流）</h2>
<p class="maodian"></p><h3>Channel</h3>
<ul><li>类似队列，生产者和消费者解耦</li></ul>
<div class="jb51code"><pre class="brush:java;">val channel = Channel<Int>()
scope.launch {
for (i in 1..5) channel.send(i)
channel.close()
}
scope.launch {
for (i in channel) {
   println(i)
}
}</pre></div>
<p class="maodian"></p><h3>Flow</h3>
<ul><li>Kotlin 原生的冷流，支持各种操作符</li></ul>
<div class="jb51code"><pre class="brush:java;">fun fetchNumbers(): Flow<Int> = flow {
for (i in 1..5) {
   delay(100)
   emit(i)
}
}
scope.launch {
fetchNumbers()
   .map { it * 2 }
   .filter { it > 5 }
   .collect { println(it) }
}</pre></div>
<p class="maodian"></p><h2>7️⃣ 高级技巧</h2>
<ul><li><strong>组合多个异步源</strong></li></ul>
<div class="jb51code"><pre class="brush:java;">val flow1 = flow { emit(fetchData1()) }
val flow2 = flow { emit(fetchData2()) }
flow1.combine(flow2) { d1, d2 -> d1 + d2 }
.collect { println(it) }</pre></div>
<ul><li><strong>懒启动的 async</strong></li></ul>
<div class="jb51code"><pre class="brush:java;">val deferred = async(start = CoroutineStart.LAZY) { fetchData() }
deferred.await() // 真正开始执行</pre></div>
<ul><li><strong>异常隔离</strong>
<ul><li>使用 <code>SupervisorJob()</code> 避免一个子协程挂掉影响整个父协程</li></ul></li></ul>
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Android协程高级用法大全