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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.
import 'dart:async';
import 'dart:html' as html;
import 'dart:js_util';
import 'dart:ui_web' as ui_web;
import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'package:url_launcher_platform_interface/link.dart';
/// The unique identifier for the view type to be used for link platform views.
const String linkViewType = '__url_launcher::link';
/// The name of the property used to set the viewId on the DOM element.
const String linkViewIdProperty = '__url_launcher::link::viewId';
/// Signature for a function that takes a unique [id] and creates an HTML element.
typedef HtmlViewFactory = html.Element Function(int viewId);
/// Factory that returns the link DOM element for each unique view id.
HtmlViewFactory get linkViewFactory => LinkViewController._viewFactory;
/// The delegate for building the [Link] widget on the web.
/// It uses a platform view to render an anchor element in the DOM.
class WebLinkDelegate extends StatefulWidget {
/// Creates a delegate for the given [link].
const WebLinkDelegate(, {super.key});
/// Information about the link built by the app.
final LinkInfo link;
WebLinkDelegateState createState() => WebLinkDelegateState();
/// The link delegate used on the web platform.
/// For external URIs, it lets the browser do its thing. For app route names, it
/// pushes the route name to the framework.
class WebLinkDelegateState extends State<WebLinkDelegate> {
late LinkViewController _controller;
void didUpdateWidget(WebLinkDelegate oldWidget) {
if ( != {
if ( != {
Future<void> _followLink() {
return Future<void>.value();
Widget build(BuildContext context) {
return Stack(
fit: StackFit.passthrough,
children: <Widget>[
context, ? null : _followLink,
child: PlatformViewLink(
viewType: linkViewType,
onCreatePlatformView: (PlatformViewCreationParams params) {
_controller = LinkViewController.fromParams(params);
return _controller
(BuildContext context, PlatformViewController controller) {
return PlatformViewSurface(
controller: controller,
gestureRecognizers: const <Factory<
hitTestBehavior: PlatformViewHitTestBehavior.transparent,
/// Controls link views.
class LinkViewController extends PlatformViewController {
/// Creates a [LinkViewController] instance with the unique [viewId].
LinkViewController(this.viewId) {
if (_instances.isEmpty) {
// This is the first controller being created, attach the global click
// listener.
_clickSubscription = html.window.onClick.listen(_onGlobalClick);
_instances[viewId] = this;
/// Creates and initializes a [LinkViewController] instance with the given
/// platform view [params].
factory LinkViewController.fromParams(
PlatformViewCreationParams params,
) {
final int viewId =;
final LinkViewController controller = LinkViewController(viewId);
controller._initialize().then((_) {
/// Because _initialize is async, it can happen that [LinkViewController.dispose]
/// may get called before this `then` callback.
/// Check that the `controller` that was created by this factory is not
/// disposed before calling `onPlatformViewCreated`.
if (_instances[viewId] == controller) {
return controller;
static final Map<int, LinkViewController> _instances =
<int, LinkViewController>{};
static html.Element _viewFactory(int viewId) {
return _instances[viewId]!._element;
static int? _hitTestedViewId;
static late StreamSubscription<html.MouseEvent> _clickSubscription;
static void _onGlobalClick(html.MouseEvent event) {
final int? viewId = getViewIdFromTarget(event);
// After the DOM click event has been received, clean up the hit test state
// so we can start fresh on the next click.
/// Call this method to indicate that a hit test has been registered for the
/// given [controller].
/// The [onClick] callback is invoked when the anchor element receives a
/// `click` from the browser.
static void registerHitTest(LinkViewController controller) {
_hitTestedViewId = controller.viewId;
/// Removes all information about previously registered hit tests.
static void unregisterHitTest() {
_hitTestedViewId = null;
final int viewId;
late html.Element _element;
Future<void> _initialize() async {
_element = html.Element.tag('a');
setProperty(_element, linkViewIdProperty, viewId);
..opacity = '0'
..display = 'block'
..width = '100%'
..height = '100%'
..cursor = 'unset';
// This is recommended on MDN:
// -
_element.setAttribute('rel', 'noreferrer noopener');
final Map<String, dynamic> args = <String, dynamic>{
'id': viewId,
'viewType': linkViewType,
await SystemChannels.platform_views.invokeMethod<void>('create', args);
void _onDomClick(html.MouseEvent event) {
final bool isHitTested = _hitTestedViewId == viewId;
if (!isHitTested) {
// There was no hit test registered for this click. This means the click
// landed on the anchor element but not on the underlying widget. In this
// case, we prevent the browser from following the click.
if (_uri != null && _uri!.hasScheme) {
// External links will be handled by the browser, so we don't have to do
// anything.
// A uri that doesn't have a scheme is an internal route name. In this
// case, we push it via Flutter's navigation system instead of letting the
// browser handle it.
final String routeName = _uri.toString();
pushRouteNameToFramework(null, routeName);
Uri? _uri;
/// Set the [Uri] value for this link.
/// When Uri is null, the `href` attribute of the link is removed.
void setUri(Uri? uri) {
_uri = uri;
if (uri == null) {
} else {
String href = uri.toString();
// in case an internal uri is given, the url mus be properly encoded
// using the currently used [UrlStrategy]
if (!uri.hasScheme) {
href = ui_web.urlStrategy?.prepareExternalUrl(href) ?? href;
_element.setAttribute('href', href);
/// Set the [LinkTarget] value for this link.
void setTarget(LinkTarget target) {
_element.setAttribute('target', _getHtmlTarget(target));
String _getHtmlTarget(LinkTarget target) {
switch (target) {
case LinkTarget.defaultTarget:
case LinkTarget.self:
return '_self';
case LinkTarget.blank:
return '_blank';
// The enum comes from a different package, which could get a new value at
// any time, so provide a fallback that ensures this won't break when used
// with a version that contains new values. This is deliberately outside
// the switch rather than a `default` so that the linter will flag the
// switch as needing an update.
return '_self';
Future<void> clearFocus() async {
// Currently this does nothing on Flutter Web.
// TODO(het): Implement this. See
Future<void> dispatchPointerEvent(PointerEvent event) async {
// We do not dispatch pointer events to HTML views because they may contain
// cross-origin iframes, which only accept user-generated events.
Future<void> dispose() async {
assert(_instances[viewId] == this);
if (_instances.isEmpty) {
await _clickSubscription.cancel();
await SystemChannels.platform_views.invokeMethod<void>('dispose', viewId);
/// Finds the view id of the DOM element targeted by the [event].
int? getViewIdFromTarget(html.Event event) {
final html.Element? linkElement = getLinkElementFromTarget(event);
if (linkElement != null) {
// TODO(stuartmorgan): Remove this ignore (and change to getProperty<int>)
// once the templated version is available on stable. On master (2.8) this
// is already not necessary.
// ignore: return_of_invalid_type
return getProperty(linkElement, linkViewIdProperty);
return null;
/// Finds the targeted DOM element by the [event].
/// It handles the case where the target element is inside a shadow DOM too.
html.Element? getLinkElementFromTarget(html.Event event) {
final html.EventTarget? target =;
if (target != null && target is html.Element) {
if (isLinkElement(target)) {
return target;
if (target.shadowRoot != null) {
final html.Node? child = target.shadowRoot!.lastChild;
if (child != null && child is html.Element && isLinkElement(child)) {
return child;
return null;
/// Checks if the given [element] is a link that was created by
/// [LinkViewController].
bool isLinkElement(html.Element? element) {
return element != null &&
element.tagName == 'A' &&
hasProperty(element, linkViewIdProperty);