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Flutter Host Service

info

This documentation is for Flutter SDK 2.1.x

Host Service lets the host application register named Dart functions that journey JavaScript can call with await HostService.invokeFunction(name, args, callbacks).

Functions​

registerFunction​

Future<void> registerFunction(
    String name,
    HostFunctionHandler handler,
)

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.

Parameters:

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

unregisterFunction​

Future<void> unregisterFunction(String name)

Removes a previously registered function. No-op if it is not present.

Parameters:

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

cancelAllFunctions​

Future<void> cancelAllFunctions({String reason = 'journey_cancelled'})

Rejects all in-flight host-function calls with the given reason. Typically 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'.

Classes​

HostFunctionHandler​

typedef HostFunctionHandler = Future<Object?> Function(
  HostFunctionArgs args,
  HostCallbacks callbacks,
);

Handler signature registered with Host Service. The value returned by the future resolves the script's promise; throwing rejects it with the error's string. Stream intermediate values back to the script with HostCallbacks.call before completing.

HostFunctionArgs​

class HostFunctionArgs {
    final Map<String, Object?> raw;

    Object? operator [](String key);
    T? value<T>(String key);
    T require<T>(String key);
}

Wraps the JSON args object delivered to a host function handler. value returns the value cast to T or null; require throws if the value is absent or the wrong type.

HostCallbacks​

class HostCallbacks {
    void call(String name, [Object? value]);
    bool has(String name);
}

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