SharedFlow
- Kotlin course
- Advanced
- Lesson 8/83
- 5 min
Learn shared streams with SharedFlow.
What is SharedFlow?
SharedFlow is a hot flow that broadcasts to multiple collectors at once. Unlike StateFlow it has no initial value; it only delivers values that are emitted.
It is created with MutableSharedFlow<T>(); you push values with .emit(value). New collectors only receive later emissions. It fits event driven notifications: a button click, an alert when a message arrives. The replay parameter can deliver the last N values to new collectors.
Using SharedFlow
You open a MutableSharedFlow and listen with .collect inside a launch. When another coroutine calls .emit, the collector receives the value.
Example: val flow = MutableSharedFlow<Int>(). Inside a launch you open flow.collect { v -> println(v) }; in the main flow flow.emit(1) delivers 1 to the collector. A second collect open at the same time also receives each value.
Practice Emit and collect with SharedFlow
Define val flow = MutableSharedFlow<Int>(). Inside a launch, open flow.collect { value -> println("Got: $value") }. After delay(100) call flow.emit(1), wait delay(100) and stop the collector with job.cancel().
Starter code
// SharedFlow emit and collect
// write here
fun main() = runBlocking {
}Sample solution
fun main() = runBlocking {
val flow = MutableSharedFlow<Int>()
val job = launch {
flow.collect { value -> println("Got: $value") }
}
delay(100)
flow.emit(1)
delay(100)
job.cancel()
}Expected output
Got: 1
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match SharedFlow parts
| Term | Meaning |
|---|---|
MutableSharedFlow |
Broadcast holder |
.emit |
Sends a value |
.collect |
Collecting |
replay |
Last N values |
2 Does SharedFlow have an initial value?
- Yes, always
- Only with suspend
- Only for Int
- No, it does not Correct answer
Explanation: SharedFlow has no initial value.
3 Complete the SharedFlow type parameter
val flow = MutableSharedFlow<____>()val flow = MutableSharedFlow<Int>()Explanation: SharedFlow needs a type parameter.