Android RecyclerView高频更新问题：仅更新RSSI元素而非整行

我正在开发一款按特定值列出设备的工具，设备信号由RSSI值作为指标。由于RSSI值频繁变化，RecyclerView中的列表行一直在持续更新。我刚接触RecyclerView，已经参考资料用了带DiffUtil Callback的List Adapter，但问题依然存在——整行还是会重排，设备多的时候用户很难选择。

我的DiffUtil实现： #

private val diffUtil = object : DiffUtil.ItemCallback<A>() {

    override fun areItemsTheSame(
        oldItem: A,
        newItem: A
    ): Boolean {
        return oldItem.id == newItem.id
    }

    override fun areContentsTheSame(
        oldItem: A,
        newItem: A
    ): Boolean {
        return oldItem == newItem
    }
}

Equals方法实现： #

override fun equals(other: Any?): Boolean {
    if (javaClass != other?.javaClass){
        return false
    }

    other as A

    return (id == other.id
            && name == other.name
            && address == other.address
            && selected == other.selected
            && version == other.version
            && rssi == other.rssi
            && stateOfCharge == other.stateOfCharge
            && configVersionNumber == other.configVersionNumber
            && expanded == other.expanded)
}

数据类A的字段： #

var id: Long = 0,
var name: String = "",
var address: String = "",
var selected: Boolean = false,
var version: String = Version().formattedVersion,
var voltage: Float = 0f,
var rssi: Int = 0,
var stateOfCharge: Int = 0,
var configVersionNumber: Int = 0,
var timestamp: Long = 0,
var expanded: Boolean = false

解决方案： #

1. 重写DiffUtil的getChangePayload方法 #

当前你的DiffUtil只要RSSI变化就会判定内容不同，触发整行刷新。要实现局部更新，需要重写getChangePayload，只返回变化的字段信息：

private val diffUtil = object : DiffUtil.ItemCallback<A>() {

    override fun areItemsTheSame(oldItem: A, newItem: A): Boolean {
        return oldItem.id == newItem.id
    }

    override fun areContentsTheSame(oldItem: A, newItem: A): Boolean {
        // 排除RSSI和电压这类实时变化字段，只要其他核心字段相同就返回true
        return oldItem.id == newItem.id
                && oldItem.name == newItem.name
                && oldItem.address == newItem.address
                && oldItem.selected == newItem.selected
                && oldItem.version == newItem.version
                && oldItem.stateOfCharge == newItem.stateOfCharge
                && oldItem.configVersionNumber == newItem.configVersionNumber
                && oldItem.expanded == newItem.expanded
    }

    override fun getChangePayload(oldItem: A, newItem: A): Any? {
        val payload = mutableMapOf<String, Any>()
        if (oldItem.rssi != newItem.rssi) {
            payload["rssi"] = newItem.rssi
        }
        if (oldItem.voltage != newItem.voltage) {
            payload["voltage"] = newItem.voltage
        }
        return if (payload.isEmpty()) null else payload
    }
}

2. 在Adapter中处理Payload，仅更新目标View #

修改onBindViewHolder方法，通过payload判断需要更新的部分，避免整行重绑：

override fun onBindViewHolder(holder: DeviceViewHolder, position: Int) {
    bindFixedContent(holder, currentList[position])
}

override fun onBindViewHolder(holder: DeviceViewHolder, position: Int, payloads: MutableList<Any>) {
    if (payloads.isEmpty()) {
        super.onBindViewHolder(holder, position, payloads)
    } else {
        val item = currentList[position]
        val payload = payloads[0] as Map<*, *>
        payload.forEach { (key, value) ->
            when (key) {
                "rssi" -> {
                    holder.rssiText.text = "信号: ${value as Int}dBm"
                    updateSignalIcon(holder.signalIcon, value as Int)
                }
                "voltage" -> {
                    holder.voltageText.text = "电压: ${value as Float}V"
                }
            }
        }
    }
}

private fun bindFixedContent(holder: DeviceViewHolder, item: A) {
    // 绑定所有非实时变化的内容
    holder.nameText.text = item.name
    holder.addressText.text = item.address
    holder.versionText.text = item.version
    // 初始化实时字段的显示
    holder.rssiText.text = "信号: ${item.rssi}dBm"
    updateSignalIcon(holder.signalIcon, item.rssi)
    holder.voltageText.text = "电压: ${item.voltage}V"
}

3. 控制数据更新频率，减少不必要刷新 #

RSSI变化极快，建议做防抖处理，合并短时间内的多次更新，避免频繁触发DiffUtil计算：

private var updateJob: Job? = null

fun updateDeviceList(newDevices: List<A>) {
    updateJob?.cancel()
    updateJob = CoroutineScope(Dispatchers.Main).launch {
        delay(150) // 延迟150毫秒，合并这段时间内的RSSI变化
        adapter.submitList(newDevices)
    }
}

内容的提问来源于stack exchange，提问作者Ron Weasley