Flow 和 LiveData 之操作符：throttleFirst、 throttleLast 、throttleLatest、debounce

Flow 和 LiveData 之操作符：throttleFirst、 throttleLast 、throttleLatest、debounce

前言

因为使用kotlin 和协程后准备移除RxJava，其中大部分功能，可以使用Flow进行替代，但是出现了部分操作符功能缺少，所有进行改进。

这是一遍没有检验的文章，部分操作操作符只是按逻辑写的，没有测试。有几个只是按自己的需求写的，可能和RxJava的存在差异

一、Flow 之操作符扩展

1. ThrottleFirst

fun <T> Flow<T>.throttleFirst(duration: Long = 1000L) = this.throttleFirstImpl(duration)

fun <T> Flow<T>.throttleFirstImpl(periodMillis: Long): Flow<T> {
    return flow {
        var lastTime = 0L
        collect { value ->
            val currentTime = System.currentTimeMillis()
            if (currentTime - lastTime >= periodMillis) {
                lastTime = currentTime
                emit(value)
            }
        }
    }
}

2. ThrottleLast

fun <T> Flow<T>.throttleLast(duration: Long = 1000L) = this.sample(duration)

3. ThrottleLatest

fun <T> Flow<T>.throttleLatest(duration: Long = 1000L) = this.throttleLatestImpl(duration)

internal fun <T> Flow<T>.throttleLatestImpl(periodMillis: Long): Flow<T> {
    return channelFlow {
        var lastValue: T?
        var timer: Timer? = null
        onCompletion { timer?.cancel() }
        collect { value ->
            lastValue = value
            if (timer == null) {
                timer = Timer()
                timer?.scheduleAtFixedRate(
                    object : TimerTask() {
                        override fun run() {
                            val value = lastValue
                            lastValue = null
                            if (value != null) {
                                launch {
                                    send(value as T)
                                }
                            } else {
                                timer?.cancel()
                                timer = null
                            }
                        }
                    },
                    0,
                    periodMillis
                )
            }
        }
    }
}

4. Debounce (Flow自带)

flow {
    emit(1)
    delay(90.milliseconds)
    emit(2)
    delay(90.milliseconds)
    emit(3)
    delay(1010.milliseconds)
    emit(4)
    delay(1010.milliseconds)
    emit(5)
}.debounce(1000.milliseconds)

一、LiveData 之操作符扩展

1. ThrottleFirst

/*** @Author stj
 * * @Date 2021/10/8-18:38
 * * @Email 375105540@qq.com
 * * 间隔固定时间内，取第一个的值
 */
fun <T> LiveData<T>.throttleFirst(duration: Long = 1000L) = MediatorLiveData<T>().also { mld ->
    val source = this
    val handler = Handler(Looper.getMainLooper())
    val isUpdate = AtomicBoolean(true)

    val runnable = Runnable {
        isUpdate.set(true)
    }

    mld.addSource(source) {
        if (isUpdate.compareAndSet(true,false)){
            mld.value = source.value
            handler.postDelayed(runnable, duration)
        }
    }
}

2. ThrottleLast

fun <T> LiveData<T>.throttleLast(duration: Long = 1000L) = MediatorLiveData<T>().also { mld ->
    val source = this
    val handler = Handler(Looper.getMainLooper())
    val isUpdate = AtomicBoolean(true)

    val runnable = Runnable {
        if (isUpdate.compareAndSet(false,true)){
            mld.value = source.value
        }
    }

    mld.addSource(source) {
        if (isUpdate.compareAndSet(true,false)) {
            handler.postDelayed(runnable, duration)
        }
    }
}

3. ThrottleLatest

fun <T> LiveData<T>.throttleLatest(duration: Long = 1000L) = MediatorLiveData<T>().also { mld ->

    val source = this
	val isFirst = AtomicBoolean(true)
    val handler =  HandlerCompat.createAsync(Looper.getMainLooper())
    val isUpdate = AtomicBoolean(true)

    val runnable = Runnable {
        if (isUpdate.compareAndSet(false,true)){
            mld.value = source.value
        }
    }

    mld.addSource(source) {
        if (isFirst.compareAndSet(true,false)){
            mld.value = source.value
        }
        if (isUpdate.compareAndSet(true,false)) {
            handler.postDelayed(runnable, duration)
        }
    }
}

4. Debounce

fun <T> LiveData<T>.debounce(duration: Long = 1000L) = MediatorLiveData<T>().also { mld ->
    val source = this
    val handler = HandlerCompat.createAsync(Looper.getMainLooper())

    val runnable = Runnable {
        mld.value = source.value
    }

    mld.addSource(source) {
        handler.removeCallbacks(runnable)
        handler.postDelayed(runnable, duration)
    }
}

Tip

有几个没有测试过，因为需求需要了，所有改了几个，其他结果是按逻辑写的，可能会有问题