Android 如何将子Activity的按键事件传递给父Activity处理

Android 的按键事件仅分发到当前前台处于活跃状态的 Activity，Activity2 启动后位于 Activity 栈顶，处于前台可见状态，所有按键事件只会派发到 Activity2 所属的 Window 体系。你在 Activity2 的 onKeyDown/onKeyUp 返回 false，事件只会继续分发给 Activity2 内部的 DecorView、子 View 处理，不会传递给后台处于暂停状态的 Activity1，所以之前的尝试无法实现需求。

方案1：本地广播实现（原生无需引入第三方依赖，推荐） #

通过本地广播跨 Activity 传递按键事件，不会对外泄露事件，实现逻辑简单：

修正后的 Activity2 代码 #

class activity2: Activity(){
    override fun onCreate(){
        // set view
    }
    override fun onKeyDown(keyCode: Int, event: KeyEvent?): Boolean {
        // 发送本地广播携带按键参数
        val intent = Intent("com.myapp.KEY_EVENT")
        intent.putExtra("keyCode", keyCode)
        intent.putExtra("keyEvent", event)
        LocalBroadcastManager.getInstance(this).sendBroadcast(intent)
        // 不需要保留Activity2默认按键行为返回true，要保留默认行为（比如按返回键关闭Activity2）则返回super.onKeyDown(keyCode, event)
        return true
    }
    override fun onKeyUp(keyCode: Int, event: KeyEvent?): Boolean {
        // 按需求决定是否要传递up事件，不需要可删除该方法重写
        val intent = Intent("com.myapp.KEY_EVENT")
        intent.putExtra("keyCode", keyCode)
        intent.putExtra("keyEvent", event)
        intent.putExtra("isKeyUp", true)
        LocalBroadcastManager.getInstance(this).sendBroadcast(intent)
        return true
    }
}

修正后的 Activity1 代码 #

class activity1: Activity(){
    // 定义广播接收器处理按键事件
    private val keyEventReceiver = object : BroadcastReceiver() {
        override fun onReceive(context: Context?, intent: Intent?) {
            intent ?: return
            val keyCode = intent.getIntExtra("keyCode", KeyEvent.KEYCODE_UNKNOWN)
            val event = intent.getParcelableExtra<KeyEvent>("keyEvent")
            val isKeyUp = intent.getBooleanExtra("isKeyUp", false)
            if(isKeyUp){
                onKeyUp(keyCode, event)
            }else{
                onKeyDown(keyCode, event)
            }
        }
    }

    override fun onCreate(){
        // set view
        // launch activity2
        launchactivy2()
    }
    override fun onResume() {
        super.onResume()
        // 注册广播接收器
        LocalBroadcastManager.getInstance(this)
            .registerReceiver(keyEventReceiver, IntentFilter("com.myapp.KEY_EVENT"))
    }

    override fun onPause() {
        super.onPause()
        // 注销广播避免内存泄漏
        LocalBroadcastManager.getInstance(this)
            .unregisterReceiver(keyEventReceiver)
    }

    fun launchactivy2(){
        val playIntent = Intent("android.intent.action.VIEW")
        playIntent.putExtra("position", "top")
        playIntent.component = ComponentName(
                "com.myapp.package",
            "com.myapp.package.activity2"
        )
        context.startActivity(playIntent)
    }
    override fun onKeyDown(keyCode: Int, event: KeyEvent?): Boolean {
        // Handle keys here
        return super.onKeyDown(keyCode, event)
    } 
}

方案2：全局回调接口实现（适合同APP内高频事件传递） #

通过 Application 类存储全局回调实例，直接传递事件性能更高：

1. 首先自定义回调接口

interface KeyEventCallback {
    fun onKeyReceived(keyCode: Int, event: KeyEvent?, isKeyUp: Boolean = false)
}

2. 在自定义 Application 类中添加回调变量

class MyApp : Application() {
    var keyEventCallback: KeyEventCallback? = null
}

3. Activity1 中注册/注销回调

override fun onResume() {
    super.onResume()
    (application as MyApp).keyEventCallback = object : KeyEventCallback {
        override fun onKeyReceived(keyCode: Int, event: KeyEvent?, isKeyUp: Boolean) {
            if(isKeyUp){
                onKeyUp(keyCode, event)
            }else{
                onKeyDown(keyCode, event)
            }
        }
    }
}

override fun onPause() {
    super.onPause()
    // 清空回调避免内存泄漏
    (application as MyApp).keyEventCallback = null
}

4. Activity2 中触发回调

override fun onKeyDown(keyCode: Int, event: KeyEvent?): Boolean {
    (application as MyApp).keyEventCallback?.onKeyReceived(keyCode, event)
    return true
}

override fun onKeyUp(keyCode: Int, event: KeyEvent?): Boolean {
    (application as MyApp).keyEventCallback?.onKeyReceived(keyCode, event, true)
    return true
}

• 如果需要保留 Activity2 的默认按键行为，发送事件后可继续调用 super.onKeyDown/super.onKeyUp 或返回 false；如果不需要默认行为，发送事件后直接返回 true 即可。
• 广播接收器、全局回调必须在 Activity1 的 onPause/onDestroy 生命周期中注销，避免内存泄漏。

内容的提问来源于stack exchange，提问作者Anil Arrabole