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// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// @dart = 2.12
part of dart.ui;
/// A wrapper for a raw callback handle.
/// This is the return type for [PluginUtilities.getCallbackHandle].
class CallbackHandle {
/// Create an instance using a raw callback handle.
/// Only values produced by a call to [CallbackHandle.toRawHandle] should be
/// used, otherwise this object will be an invalid handle.
: assert(_handle != null, "'_handle' must not be null.");
final int _handle;
/// Get the raw callback handle to pass over a [MethodChannel] or [SendPort]
/// (to pass to another [Isolate]).
int toRawHandle() => _handle;
bool operator ==(Object other) {
if (runtimeType != other.runtimeType)
return false;
return other is CallbackHandle
&& other._handle == _handle;
int get hashCode => _handle.hashCode;
/// Functionality for Flutter plugin authors.
/// See also:
/// * [IsolateNameServer], which provides utilities for dealing with
/// [Isolate]s.
class PluginUtilities {
// This class is only a namespace, and should not be instantiated or
// extended directly.
factory PluginUtilities._() => throw UnsupportedError('Namespace');
static Map<Function, CallbackHandle?> _forwardCache =
<Function, CallbackHandle?>{};
static Map<CallbackHandle, Function?> _backwardCache =
<CallbackHandle, Function?>{};
/// 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;
/// Get a tear-off of a named top-level or static callback represented by a
/// handle.
/// The `handle` argument must not be null.
/// If `handle` is not a valid handle returned by
/// [PluginUtilities.getCallbackHandle], null is returned. Otherwise, a
/// tear-off of the callback associated with `handle` is returned.
static Function? getCallbackFromHandle(CallbackHandle handle) {
assert(handle != null, "'handle' must not be null.");
return _backwardCache.putIfAbsent(
handle, () => _getCallbackFromHandle(handle.toRawHandle()));