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iOS Host Service

Host Service lets the host application register named native functions that journey JavaScript can call with await HostService.invokeFunction(name, args, callbacks). It also provides host-side utilities such as the image picker.

Functions​

registerFunction​

public func registerFunction(
    _ name: String,
    handler: @escaping HostFunctionHandler
)

Registers a named host function callable from journey JavaScript as await HostService.invokeFunction(name, args, callbacks). Re-registering the same name replaces the previous handler and logs a warning.

Parameters:

  • name: String — Unique function name as seen from JavaScript.
  • handler: HostFunctionHandler — Invoked when a script calls this function, see HostFunctionHandler.

unregisterFunction​

public func unregisterFunction(_ name: String)

Removes a registered host function. No-op if not present.

Parameters:

  • name: String — Name of the function to remove.

cancelAllFunctions​

public func cancelAllFunctions(reason: String = "journey_cancelled")

Rejects every in-flight HostService.invokeFunction call with the given reason. Called when the journey hosting the JavaScript runtime is dismissed or cancelled.

Parameters:

  • reason: String — Rejection reason delivered to the scripts. Defaults to "journey_cancelled".

pickImage​

public func pickImage(
    source: ImagePickerSource = .choose,
    maxCount: Int = 1,
    maxWidth: Int = 512,
    maxHeight: Int = 512,
    quality: Double = 0.7,
    onSuccess: @escaping ([String]) -> Void,
    onError: ((Error) -> Void)? = nil
)

Presents the system image picker (gallery, camera, or a chooser), resizes the selected images, and returns their local file paths.

Parameters:

  • source: ImagePickerSource — Image source, see ImagePickerSource. Defaults to .choose.
  • maxCount: Int — Maximum number of images the user can select. Defaults to 1.
  • maxWidth: Int — Maximum width of the resized images. Defaults to 512.
  • maxHeight: Int — Maximum height of the resized images. Defaults to 512.
  • quality: Double — JPEG compression quality between 0 and 1. Defaults to 0.7.
  • onSuccess: ([String]) -> Void — Called with local file paths of the processed images.
  • onError: ((Error) -> Void)? — Called when picking fails or the user cancels.

Classes​

HostFunctionHandler​

public typealias HostFunctionHandler = (
    _ args: HostFunctionArgs,
    _ callbacks: HostCallbacks,
    _ resolve: @escaping (Any?) -> Void,
    _ reject: @escaping (String) -> Void
) -> Void

Handler signature registered with Host Service. Exactly one of resolve / reject must be called: resolve fulfills the script's promise with the given value, reject rejects it with the given message.

HostFunctionArgs​

public struct HostFunctionArgs {
    public let raw: [String: Any]

    public subscript(key: String) -> Any? { get }
    public func value<T>(_ key: String) -> T?
    public func require<T>(_ key: String) throws -> T
    public func decode<T: Decodable>(_ key: String, as type: T.Type = T.self) throws -> T
}

Wraps the JSON args dictionary delivered to a host function handler. value returns the value cast to T or nil; require throws HostFunctionError if absent or the wrong type; decode decodes a JSON-compatible field into a Decodable type.

HostCallbacks​

public final class HostCallbacks {
    public func call(_ name: String, _ value: Any? = nil)
    public func has(_ name: String) -> Bool
}

Proxy passed to host handlers for the callback functions the script supplied. call fires a named callback with an optional value (no-op if the script did not provide it); has returns whether the script provided a callback with this name.

HostFunctionError​

public enum HostFunctionError: Error {
    case invalidArgs(String)
}

Errors a host function handler can throw before invoking resolve/reject.

ImagePickerSource​

public enum ImagePickerSource: String {
    case gallery
    case camera
    case choose
}