Add example to use channel for the "dropIfBusy" behaviour

Author: LukasLechnerDev

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/playground/flow/channels/3_drop_while_busy.kt

@@ -0,0 +1,66 @@
+package com.lukaslechner.coroutineusecasesonandroid.playground.flow.channels
+
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.channels.consumeEach
+import kotlinx.coroutines.channels.produce
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.consumeAsFlow
+import kotlinx.coroutines.flow.flow
+import kotlinx.coroutines.launch
+
+/**
+ UseCase: We want to trigger some processing. While the downstream is currently
+ busy, we want to drop the current trigger emission.
+
+ With a SharedFlow, this is not possible, since we need to define a buffer size of
+ > 0 for buffer strategies like "DROP_LATEST". Channels however have a buffer sice of 0
+ by default.
+
+ Another option is to use the custom operator "dropIfBusy" (see below)
+
+ See also: https://stackoverflow.com/questions/64844821/how-to-drop-latest-with-coroutine-flowt/74560222#74560222
+**/
+
+fun <T> Flow<T>.dropIfBusy(): Flow<T> = flow {
+    coroutineScope {
+        val channel = produce {
+            collect { trySend(it) }
+        }
+        channel.consumeEach { emit(it) }
+    }
+}
+
+suspend fun main(): Unit = coroutineScope {
+
+    val channel = Channel<Int>()
+
+    launch {
+        channel
+            .consumeAsFlow()
+            .collect {
+                println("Process $it")
+                delay(1000)
+                println("$it processed")
+            }
+    }
+
+    launch {
+
+        delay(100)
+
+        // 1 should be processed
+        channel.trySend(1)
+        println("sharedFlow emits 1")
+
+        // 2 should not be processed since downstream is busy
+        channel.trySend(2)
+        println("sharedFlow emits 2")
+
+        // 3 should be processed again
+        delay(2000)
+        channel.trySend(3)
+        println("sharedFlow emits 3")
+    }
+}