I have a flow that I use ` collect ` on however I want to wa

Question

I have a flow that I use ` collect ` on however I want to wait for a StateFlow Boolean to be true before the collection can proceed what is the recommended way of currently handling this None of the emits can be dropped they need to wait for the StateFlow Boolean to be true and emit as soon as it changes

simon.vergauwen · Answer

```flow stateFlow first it == true originalFlow collect this ``` You can create a new flow that awaits the first `true` signal from `StateFlow` and then it collects the original flow

Joakim Forslund · Answer

Thanks for the pointer i ll check it out

Joffrey · Answer

< simon vergauwen> I think the `collect ` that is chained after the `first ` call is a mistake typo `first ` is already a terminal operator

simon.vergauwen · Answer

Thank you < Joffrey> that is indeed a mistake then I wrote this from memory

ursus · Answer

`stateFlow filter it == true take 1 flatMap originalFlow `

Joakim Forslund · Answer

Thanks people

Joakim Forslund · Answer

```suspend fun lt T gt Flow lt T gt waitForTrue stateFlow StateFlow lt Boolean gt Flow lt T gt stateFlow first it return this ``` Became the result which seems kind of silly but yeah `first` is suspending without being terminating so it is a way to solve it

Joffrey · Answer

The problem is that the operator that you created isn t cold anymore it has to suspend at the moment it s called instead of when the flow is collected

Joakim Forslund · Answer

Is it a problem though The only real effect I care about in this instance is that it block any ` collect` calls from proceeding

Joakim Forslund · Answer

The data is waiting to be collected is indeed put into a suspended state and will proceed when the stateFlow changes

simon.vergauwen · Answer

I d say it s a problem since now you re waiting on stateFlow to constructor the `Flow` which has no influence on the collection

Joakim Forslund · Answer

And doing ```suspend fun lt T gt Flow lt T gt waitForTrue2 stateFlow StateFlow lt Boolean gt Flow lt T gt return flow stateFlow first it this waitForTrue2 collect this ``` Would then adhere to this

Joakim Forslund · Answer

or must it basically be a replacement for ` collect` all together

simon.vergauwen · Answer

No this is the replacement for `collect` The lambda inside `flow ` is executd when you call `collect` So first it will await the boolean and then it ll collect the original flow

Joakim Forslund · Answer

Right it makes sense

Joffrey · Answer

Your new version is fine it s basically < simon vergauwen> s initial suggestion as an extension function however you don t need the `suspend` keyword anymore wink Calling this operator immediately constructs the new flow without waiting Collectors of this flow are the ones that will suspend when actually collecting

Joakim Forslund · Answer

Allright thanks for clearing things up slightly smiling face