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hrach/share.kt

Last active December 4, 2019 10:42
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Flow<T>.share() operator - caches the latest value
Raw
share.kt
import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
import kotlinx.coroutines.flow.*
import java.util.concurrent.atomic.AtomicInteger
fun <T> Flow<T>.share(): Flow<T> {
val channel = ConflatedBroadcastChannel<T>()
val counter = AtomicInteger()
var job: Job? = null
return channel
.asFlow()
.onStart {
if (counter.incrementAndGet() == 1) {
job = GlobalScope.launch {
this@share
.catch {
channel.close(it)
}
.collect {
channel.offer(it)
}
}
}
}
.onCompletion {
if (counter.decrementAndGet() == 0) {
job?.cancelAndJoin()
job = null
}
}
}
Raw
test_activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<TextView
android:id="@+id/tv1"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/tv2"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<Button
android:id="@+id/btn1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="JOB A" />
<Button
android:id="@+id/btn2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="JOB B" />
</LinearLayout>
Raw
test_MainActivity.kt
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.lifecycleScope
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
var jobA: Job? = null
var jobB: Job? = null
val flow: Flow<Int> = flow {
var i = 0
while (true) {
emit(i++)
delay(500)
}
}.share()
btn1.setOnClickListener {
if (jobA == null) {
jobA = lifecycleScope.launch {
flow
.collect {
tv1.text = it.toString()
}
}
} else {
jobA?.cancel()
jobA = null
}
}
btn2.setOnClickListener {
if (jobB == null) {
jobB = lifecycleScope.launch {
flow
.collect {
tv2.text = it.toString()
}
}
} else {
jobB?.cancel()
jobB = null
}
}
}
}
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