registerNumericServiceExtension method

  1. @protected
void registerNumericServiceExtension ({@required String name, @required AsyncValueGetter<double> getter, @required AsyncValueSetter<double> setter })
@protected

Registers a service extension method with the given name (full name "ext.flutter.name"), which takes a single argument with the same name as the method which, if present, must have a value that can be parsed by double.parse, and can be omitted to read the current value. (Other arguments are ignored.)

Calls the getter callback to obtain the value when responding to the service extension method being called.

Calls the setter callback with the new value when the service extension method is called with a new value.

A registered service extension can only be activated if the vm-service is included in the build, which only happens in debug and profile mode. Although a service extension cannot be used in release mode its code may still be included in the Dart snapshot and blow up binary size if it is not wrapped in a guard that allows the tree shaker to remove it (see sample code below).

Sample Code

The following code registers a service extension that is only included in debug builds:

assert(() {
  // Register your service extension here.
  return true;
}());

A service extension registered with the following code snippet is available in debug and profile mode:

if (!const bool.fromEnvironment('dart.vm.product')) {

Both guards ensure that Dart's tree shaker can remove the code for the service extension in release builds.

Implementation 

@protected
void registerNumericServiceExtension({
  @required String name,
  @required AsyncValueGetter<double> getter,
  @required AsyncValueSetter<double> setter
}) {
  assert(name != null);
  assert(getter != null);
  assert(setter != null);
  registerServiceExtension(
    name: name,
    callback: (Map<String, String> parameters) async {
      if (parameters.containsKey(name))
        await setter(double.parse(parameters[name]));
      return <String, dynamic>{ name: (await getter()).toString() };
    }
  );
}