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https://speakerdeck.com/hkusu/extension-functions-for-livedata で説明したコードですが https://gist.github.com/hkusu/6bdc35e75614df559135174535e3c3ce の方が新しいです
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| package io.github.hkusu.sample.ext | |
| import androidx.lifecycle.LiveData | |
| import androidx.lifecycle.MediatorLiveData | |
| import androidx.lifecycle.Observer | |
| import kotlinx.coroutines.CoroutineScope | |
| import kotlinx.coroutines.launch | |
| import kotlin.coroutines.CoroutineContext | |
| inline fun <T, U> LiveData<T>.mapNotNull( | |
| crossinline block: (T) -> U? // null または戻り値なしの return で更新をキャンセルできるように | |
| ): LiveData<U> { | |
| val result = MediatorLiveData<U>() | |
| result.addSource(this) { t -> | |
| block.invoke(t)?.takeUnless { it is Unit }?.let { result.value = it } | |
| } | |
| return result | |
| } | |
| // 現状では inline fun とすると落ちる https://github.com/Kotlin/kotlinx.coroutines/issues/1150 | |
| fun <T, U> LiveData<T>.coMap( | |
| coroutineScope: CoroutineScope, // 通常は ViewModel の viewModelScope を渡す | |
| coroutineContext: CoroutineContext = coroutineScope.coroutineContext, // context を切り替えたい場合に利用(例: Dispatchers.IO)。block 中で withContext で切り替えても可 | |
| block: suspend (T) -> U // liveData-ktx の map に合わせて T は NotNull にしているが null が渡されうる | |
| ): LiveData<U> { | |
| val result = MediatorLiveData<U>() | |
| result.addSource(this) { | |
| coroutineScope.launch(coroutineContext) { | |
| result.postValue(block.invoke(it)) // mainスレッド以外からも更新できるように | |
| } | |
| } | |
| return result | |
| } | |
| // この拡張関数を利用しない場合、 | |
| // val hogeLiveData = fugalLveData.switchMap { | |
| // liveData(viewModelScope.coroutineContext) { | |
| // emit("hoge") | |
| // } | |
| // } | |
| // のようにも書ける | |
| fun <T, U> LiveData<T>.coMapNotNull( | |
| coroutineScope: CoroutineScope, | |
| coroutineContext: CoroutineContext = coroutineScope.coroutineContext, | |
| block: suspend (T) -> U? | |
| ): LiveData<U> { | |
| val result = MediatorLiveData<U>() | |
| result.addSource(this) { t -> | |
| coroutineScope.launch(coroutineContext) { | |
| block.invoke(t)?.takeUnless { it is Unit }?.let { result.postValue(it) } | |
| } | |
| } | |
| return result | |
| } | |
| inline fun <T1, T2, U> merge( | |
| liveData1: LiveData<T1>, | |
| liveData2: LiveData<T2>, | |
| crossinline block: (T1?, T2?) -> U? | |
| ): LiveData<U> { | |
| val result = MediatorLiveData<U>() | |
| result.addSource(liveData1) { t1 -> | |
| block.invoke(t1, liveData2.value)?.takeUnless { it is Unit }?.let { result.value = it } | |
| } | |
| result.addSource(liveData2) { t2 -> | |
| block.invoke(liveData1.value, t2)?.takeUnless { it is Unit }?.let { result.value = it } | |
| } | |
| return result | |
| } | |
| inline fun <T1, T2, T3, U> merge( | |
| liveData1: LiveData<T1>, | |
| liveData2: LiveData<T2>, | |
| liveData3: LiveData<T3>, | |
| crossinline block: (T1?, T2?, T3?) -> U? | |
| ): LiveData<U> { | |
| val result = MediatorLiveData<U>() | |
| result.addSource(liveData1) { t1 -> | |
| block.invoke(t1, liveData2.value, liveData3.value)?.takeUnless { it is Unit }?.let { result.value = it } | |
| } | |
| result.addSource(liveData2) { t2 -> | |
| block.invoke(liveData1.value, t2, liveData3.value)?.takeUnless { it is Unit }?.let { result.value = it } | |
| } | |
| result.addSource(liveData3) { t3 -> | |
| block.invoke(liveData1.value, liveData2.value, t3)?.takeUnless { it is Unit }?.let { result.value = it } | |
| } | |
| return result | |
| } | |
| fun <T1, T2, U> coMerge( | |
| liveData1: LiveData<T1>, | |
| liveData2: LiveData<T2>, | |
| coroutineScope: CoroutineScope, | |
| coroutineContext: CoroutineContext = coroutineScope.coroutineContext, | |
| block: suspend (T1?, T2?) -> U? | |
| ): LiveData<U> { | |
| val result = MediatorLiveData<U>() | |
| result.addSource(liveData1) { t1 -> | |
| coroutineScope.launch(coroutineContext) { | |
| block.invoke(t1, liveData2.value)?.takeUnless { it is Unit }?.let { result.postValue(it) } | |
| } | |
| } | |
| result.addSource(liveData2) { t2 -> | |
| coroutineScope.launch(coroutineContext) { | |
| block.invoke(liveData1.value, t2)?.takeUnless { it is Unit }?.let { result.postValue(it) } | |
| } | |
| } | |
| return result | |
| } | |
| fun <T1, T2, T3, U> coMerge( | |
| liveData1: LiveData<T1>, | |
| liveData2: LiveData<T2>, | |
| liveData3: LiveData<T3>, | |
| coroutineScope: CoroutineScope, | |
| coroutineContext: CoroutineContext = coroutineScope.coroutineContext, | |
| block: suspend (T1?, T2?, T3?) -> U? | |
| ): LiveData<U> { | |
| val result = MediatorLiveData<U>() | |
| result.addSource(liveData1) { t1 -> | |
| coroutineScope.launch(coroutineContext) { | |
| block.invoke(t1, liveData2.value, liveData3.value)?.takeUnless { it is Unit }?.let { result.postValue(it) } | |
| } | |
| } | |
| result.addSource(liveData2) { t2 -> | |
| coroutineScope.launch(coroutineContext) { | |
| block.invoke(liveData1.value, t2, liveData3.value)?.takeUnless { it is Unit }?.let { result.postValue(it) } | |
| } | |
| } | |
| result.addSource(liveData3) { t3 -> | |
| coroutineScope.launch(coroutineContext) { | |
| block.invoke(liveData1.value, liveData2.value, t3)?.takeUnless { it is Unit }?.let { result.postValue(it) } | |
| } | |
| } | |
| return result | |
| } | |
| inline fun <T> LiveData<T>.filter( | |
| crossinline block: (T) -> Boolean | |
| ): LiveData<T> { | |
| val result = MediatorLiveData<T>() | |
| result.addSource(this) { | |
| if (block.invoke(it)) { | |
| result.value = it | |
| } | |
| } | |
| return result | |
| } | |
| fun <T> LiveData<T>.coFilter( | |
| coroutineScope: CoroutineScope, | |
| coroutineContext: CoroutineContext = coroutineScope.coroutineContext, | |
| block: suspend (T) -> Boolean | |
| ): LiveData<T> { | |
| val result = MediatorLiveData<T>() | |
| result.addSource(this) { | |
| coroutineScope.launch(coroutineContext) { | |
| if (block.invoke(it)) { | |
| result.postValue(it) | |
| } | |
| } | |
| } | |
| return result | |
| } | |
| class Observe<T>(private val liveData: LiveData<T>) { | |
| private val observer = Observer<T> {} | |
| fun start() { | |
| liveData.observeForever(observer) | |
| } | |
| fun cancel() { | |
| liveData.removeObserver(observer) | |
| } | |
| } | |
| fun <T> LiveData<T>.observe(): Observe<T> = Observe(this).apply { start() } |
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