android 之 Kotlin中Handler的使用

在 Android Kotlin 开发中，Handler主要用于​​线程间通信​​（如后台线程更新 UI）和​​延迟任务调度​​。以下是关键用法、示例及注意事项，结合最佳实践和内存安全方案：

class MainActivity : AppCompatActivity() {private lateinit var binding: ActivityMainBinding// 绑定主线程 Looperprivate val mainHandler = Handler(Looper.getMainLooper())override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)binding = ActivityMainBinding.inflate(layoutInflater)setContentView(binding.root)// 在后台线程执行耗时任务thread {Thread.sleep(2000) // 模拟耗时操作// 通过 Handler 切回主线程更新 UImainHandler.post {binding.textView.text = "后台任务完成，主线程更新 UI"}}}
}

• 关键点​​：Handler(Looper.getMainLooper())确保任务在主线程执行。

• ​​场景​​：网络请求、数据库读写等后台操作后更新 UI。

2. ​​延迟执行任务​

// 延迟 3 秒显示 Toast
mainHandler.postDelayed({Toast.makeText(this, "延迟 3 秒执行", Toast.LENGTH_SHORT).show()
}, 3000)

​​注意​​：时间单位是毫秒（3000ms = 3s）

​​二、避免内存泄漏（安全写法）​​

Handler持有 Activity引用可能导致内存泄漏。解决方案：

​​方案 1：静态内部类 + 弱引用​

class SafeHandlerActivity : AppCompatActivity() {private lateinit var weakHandler: WeakReferenceHandlercompanion object {const val MSG_UPDATE_TEXT = 1}// 静态内部类，不持有外部引用class WeakReferenceHandler(activity: SafeHandlerActivity) : Handler(Looper.getMainLooper()) {private val weakRef = WeakReference(activity)override fun handleMessage(msg: Message) {val activity = weakRef.get() ?: returnwhen (msg.what) {MSG_UPDATE_TEXT -> activity.binding.textView.text = "安全更新文本"}}}override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)weakHandler = WeakReferenceHandler(this)// 发送延迟消息weakHandler.sendEmptyMessageDelayed(MSG_UPDATE_TEXT, 2000)}override fun onDestroy() {super.onDestroy()weakHandler.removeCallbacksAndMessages(null) // 移除所有回调}
}

方案 2：结合 Lifecycle​

class LifecycleAwareHandler(lifecycle: Lifecycle,looper: Looper,private val callback: (Message) -> Boolean
) : Handler(looper) {init {lifecycle.addObserver(object : LifecycleObserver {@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)fun onDestroy() {removeCallbacksAndMessages(null)lifecycle.removeObserver(this)}})}override fun handleMessage(msg: Message) {if (lifecycle.currentState.isAtLeast(Lifecycle.State.STARTED)) {callback(msg)}}
}

优势​​：自动在 onDestroy时清理消息

三、替代方案：协程（推荐）​​

现代 Android 开发中，协程更简洁且避免内存泄漏：

class CoroutineActivity : AppCompatActivity() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)lifecycleScope.launch(Dispatchers.IO) {delay(2000) // 后台延迟 2 秒withContext(Dispatchers.Main) {binding.textView.text = "协程更新 UI"}}// 主线程延迟任务lifecycleScope.launch(Dispatchers.Main) {delay(3000)Toast.makeText(this@CoroutineActivity, "协程延迟任务", Toast.LENGTH_SHORT).show()}}
}

​​依赖​​

implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.8.0"

五、总结建议​​