getCallbackHandle method Null safety

CallbackHandle? getCallbackHandle(
  1. Function callback

Get a handle to a named top-level or static callback function which can be easily passed between isolates.

The callback argument must not be null.

Returns a CallbackHandle that can be provided to PluginUtilities.getCallbackFromHandle to retrieve a tear-off of the original callback. If callback is not a top-level or static function, null is returned.


static CallbackHandle? getCallbackHandle(Function callback) {
  assert(callback != null, "'callback' must not be null.");
  return _forwardCache.putIfAbsent(callback, () {
    final int? handle = _getCallbackHandle(callback);
    return handle != null ? CallbackHandle.fromRawHandle(handle) : null;