In RxJava1 flatmap had a overloaded method that allowed you to retain source values and pass it down the stream.
I've gained this knowledge from the following blog post
However, moving to RxJava2, I cannot seem to find it. I checked the changes from Rx1 and Rx2 and it is not listed. I would like to know if it exists still but I am perhaps not looking in the right place.
I am using a Single by the way.
I don't think Single ever supported this operator and the Observable/Flowable operators are still there. You can accomplish this behavior by mapping the result of the inner source:
source.flatMap(originalValue ->
createInnerSource(originalValue)
.map(innerValue -> process(originalValue, innerValue))
)
The lambda of the map will capture the originalValue for you.
来源：https://stackoverflow.com/questions/48695024/rxjava-2-what-happen-the-resultselector-argument-of-flatmap