How to only return a flow of list when certain condition is met?-CodePudding

I have an overriden function that returns a flow of list and if the condition is not met, I emit an emptyList() to cover up the corner case:

override fun returnFlow(): Flow<List<Item>> {
    return combine(booleanFlow()) { items, boolean ->
        if (!boolean) {
            items
        } else {
            emptyList()
        }
    }
}

I want to remove the else {} logic and change it to only emitting a list when boolean is false. Ideally I would like something similar to this:

override fun returnFlow(): Flow<List<Item>> {
    return combine(booleanFlow()) { items, boolean ->
        while (!boolean) {
            items
        }
    }
}

Can I use something like cancelFlow() or return Nothing?

I tried how to stop Kotlin flow when certain condition occurs and it doesn't work since the return type changes to Flow<Unit>.

CodePudding user response：

Use combineTransform instead of combine. Instead of always emitting the item returned by the lambda, this lets you choose whether or not to emit an item by calling emit.

override fun returnFlow(): Flow<List<Item>> {
    return combineTransform(booleanFlow()) { items, boolean ->
        if (!boolean) {
            emit(items)
        }
    }
}