Android UI响应式更新：使用LiveData管理布尔状态

// 原始UI逻辑片段
if (isPlayerNearby) {
    Text("Player $playerName is within range!")
    Image(/*some image*/)
    Button(onClick = { attack() }) {
        Text(text = "ELIMINATE")
    }
} else {
    Text("No players nearby. Keep searching.")
    Image(/*some OTHER image*/)
    Button(onClick = { attack() }) { // This button should be DISABLED
        Text(text = "ELIMINATE")
    }
}

// 原始更新isPlayerNearby的逻辑片段
private var endpointDiscoveryCallback: EndpointDiscoveryCallback = object :
    EndpointDiscoveryCallback() {
    override fun onEndpointFound(endpointId: String, info: DiscoveredEndpointInfo) {
        toEndpointId = endpointId
        Nearby.getConnectionsClient(context)
            .requestConnection(getLocalUserName(), endpointId, connectionLifeCycleCallback)
            .addOnSuccessListener {
                run {
                    endpointFound()
                    // 这里设置isPlayerNearby为true，但UI不会自动更新
                    // isPlayerNearby = true 
                    Toast.makeText(applicationContext, endpointId, Toast.LENGTH_SHORT).show()
                }
            }
            .addOnFailureListener { _ ->
                // 处理连接失败
            }
    }

    override fun onEndpointLost(endpointId: String) {
        // 当端点丢失时，需要将isPlayerNearby设置为false并更新UI
        Toast.makeText(applicationContext, "Endpoint Lost", Toast.LENGTH_SHORT).show()
    }
}

// 在ViewModel中声明
class MyViewModel : ViewModel() {
    val isPlayerNearby = MutableLiveData(false) // 初始值为false
    // ... 其他逻辑
}

// 修改EndpointDiscoveryCallback中的逻辑
private var endpointDiscoveryCallback: EndpointDiscoveryCallback = object :
    EndpointDiscoveryCallback() {
    override fun onEndpointFound(endpointId: String, info: DiscoveredEndpointInfo) {
        // ... (省略部分代码)
        .addOnSuccessListener {
            run {
                endpointFound()
                // 通过ViewModel更新LiveData的值
                myViewModel.isPlayerNearby.postValue(true) // 通知所有观察者isPlayerNearby变为true
                Toast.makeText(applicationContext, endpointId, Toast.LENGTH_SHORT).show()
            }
        }
        // ...
    }

    override fun onEndpointLost(endpointId: String) {
        // 当端点丢失时，更新LiveData的值为false
        myViewModel.isPlayerNearby.postValue(false) // 通知所有观察者isPlayerNearby变为false
        Toast.makeText(applicationContext, "Endpoint Lost", Toast.LENGTH_SHORT).show()
    }
}

// 在Fragment或Activity中观察LiveData
class MyFragment : Fragment() {

    private val myViewModel: MyViewModel by viewModels() // 获取ViewModel实例

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        myViewModel.isPlayerNearby.observe(viewLifecycleOwner) { isPlayerNearby ->
            // 当isPlayerNearby的值变化时，此lambda表达式会被执行
            // 在这里更新UI以反映新的状态

            if (isPlayerNearby) {
                // 示例：更新UI显示玩家在范围内
                // 假设这里是Compose UI，或者操作传统View的可见性/文本/启用状态
                // Text("Player $playerName is within range!")
                // Image(/*some image*/)
                // Button(onClick = { attack() }) { Text(text = "ELIMINATE") }
                updateUiForPlayerNearby(true) // 假设这是一个更新UI的函数
            } else {
                // 示例：更新UI显示没有玩家在范围内
                // Text("No players nearby. Keep searching.")
                // Image(/*some OTHER image*/)
                // Button(onClick = { attack() }) { Text(text = "ELIMINATE") } // 按钮应禁用
                updateUiForPlayerNearby(false) // 假设这是一个更新UI的函数
            }
        }
    }

    // 假设这是一个处理UI更新的辅助函数，具体实现取决于你的UI框架（Compose或传统View）
    private fun updateUiForPlayerNearby(playerNearby: Boolean) {
        // 如果是Jetpack Compose，直接在Composable函数中根据isPlayerNearby状态渲染即可
        // 例如：
        // @Composable
        // fun PlayerStatusScreen(isPlayerNearby: Boolean, playerName: String, onAttackClick: () -> Unit) {
        //     if (isPlayerNearby) {
        //         Text("Player $playerName is within range!")
        //         Image(...)
        //         Button(onClick = onAttackClick) { Text("ELIMINATE") }
        //     } else {
        //         Text("No players nearby. Keep searching.")
        //         Image(...)
        //         Button(onClick = onAttackClick, enabled = false) { Text("ELIMINATE") }
        //     }
        // }

        // 如果是传统View系统，则通过findViewById更新View属性
        // val statusTextView = view?.findViewById<TextView>(R.id.status_text_view)
        // val eliminateButton = view?.findViewById<Button>(R.id.eliminate_button)
        // val playerImageView = view?.findViewById<ImageView>(R.id.player_image_view)

        // if (playerNearby) {
        //     statusTextView?.text = "Player $playerName is within range!"
        //     playerImageView?.setImageResource(R.drawable.player_nearby_image)
        //     eliminateButton?.isEnabled = true
        // } else {
        //     statusTextView?.text = "No players nearby. Keep searching."
        //     playerImageView?.setImageResource(R.drawable.no_player_nearby_image)
        //     eliminateButton?.isEnabled = false
        // }
    }
}

// 在Composable函数中
@Composable
fun PlayerStatusScreen(viewModel: MyViewModel) {
    val isPlayerNearby by viewModel.isPlayerNearby.observeAsState(initial = false) // 观察LiveData

    if (isPlayerNearby) {
        Text("Player $playerName is within range!")
        Image(/*some image*/)
        Button(onClick = { attack() }) {
            Text(text = "ELIMINATE")
        }
    } else {
        Text("No players nearby. Keep searching.")
        Image(/*some OTHER image*/)
        Button(onClick = { attack() }, enabled = false) { // 在Compose中直接设置enabled属性
            Text(text = "ELIMINATE")
        }
    }
}