MWStreamable

Overview

To start a stream, use the .stream() operators. They are available on a Publisher whose output is a MetaWear, including:

• publish()

• publishIfConnected()

• publishWhenConnected()

A .stream() operator accepts an MWStreamable instance. You can use presets that autocomplete within the operator, such as magnetometer(freq:), or construct them directly, such as init(freq:).

Some .stream() operators produce a timestamped typed output. You can collect these into an array and convert that into a String-only CSV table with aptly labeled columns by using MWDataTable, such as in the example below.

let cancel = PassthroughSubject<Void,Never>()
let config: MWStreamable = .magnetometer(freq: .hz25)
metawear
    .publishIfConnected()
    .stream(config)
    .prefix(untilOutputFrom: cancel)
    .collect()
    .map { MWDataTable(streamed: $0, config) }
    .eraseToAnyPublisher()

Multiple .stream pipelines can run independently. You can also merge the output of an arbitrary array of streams using standard operators like MergeMany, .prefix(untilOutputFrom:), and .collect() . Our open-source MetaBase 5 app provides an example in ActionVM.swift. It uses user-selected (and persisted) sensor parameters to inform the construction a container of MWStreamable configurations. Only non-nil configs are streamed. Upon cancellation, outputs merge into a single CSV file. The hyperlinked function is called as part of a loop across an arbitrary number of devices.

Unless you construct your own sensor wrappers, this protocol’s details and default methods are unlikely to be important to you.