How to get the value of a Flow outside a coroutine?

Issue

How can I get the value of a Flow outside a coroutine similarly to LiveData?

// Suspend function 'first' should be called only from a coroutine or another suspend function
flowOf(1).first()

// value is null
flowOf(1).asLiveData().value

// works
MutableLiveData(1).value

Context

I'm avoiding LiveData in the repository layer in favor of Flow. Yet, I need to set, observe and collect the value for immediate consumption. The later is useful for authentication purpose in a OkHttp3 Interceptor.

Solution

Well... what you're looking for isn't really what Flow is for. Flow is just a stream. It is not a value holder, so there is nothing for you retrieve.

So, there are two major avenues to go down, depending on what your interceptor needs.

Perhaps your interceptor can live without the data from the repository. IOW, you'll use the data if it exists, but otherwise the interceptor can continue along. In that case, you can have your repository emit a stream but also maintain a "current value" cache that your interceptor can use. That could be via:

• BroadcastChannel
• LiveData
• a simple property in the repository that you update internally and expose as a val

If your interceptor needs the data, though, then none of those will work directly, because they will all result in the interceptor getting null if the data is not yet ready. What you would need is a call that can block, but perhaps evaluates quickly if the data is ready via some form of cache. The details of that will vary a lot based on the implementation of the repository and what is supplying the Flow in the first place.

Answered By - CommonsWare