[web] Introduce the Link widget

packages/url_launcher/url_launcher/example/lib/main.dart

@@ -6,7 +6,8 @@
 
 import 'dart:async';
 
-import 'package:flutter/material.dart';
+import 'package:flutter/material.dart' hide Link;
+import 'package:flutter/rendering.dart';
 import 'package:url_launcher/url_launcher.dart';
 
 void main() {
@@ -21,20 +22,25 @@ class MyApp extends StatelessWidget {
       theme: ThemeData(
         primarySwatch: Colors.blue,
       ),
-      home: MyHomePage(title: 'URL Launcher'),
+      initialRoute: '/links',
+      routes: {
+        '/links': (BuildContext context) => LinksPage(title: 'Links'),
+        '/url_launcher': (BuildContext context) =>
+            UrlLauncherPage(title: 'URL Launcher'),
+      },
     );
   }
 }
 
-class MyHomePage extends StatefulWidget {
-  MyHomePage({Key key, this.title}) : super(key: key);
+class UrlLauncherPage extends StatefulWidget {
+  UrlLauncherPage({Key key, this.title}) : super(key: key);
   final String title;
 
   @override
-  _MyHomePageState createState() => _MyHomePageState();
+  _UrlLauncherPageState createState() => _UrlLauncherPageState();
 }
 
-class _MyHomePageState extends State<MyHomePage> {
+class _UrlLauncherPageState extends State<UrlLauncherPage> {
   Future<void> _launched;
   String _phone = '';
 
@@ -204,3 +210,132 @@ class _MyHomePageState extends State<MyHomePage> {
     );
   }
 }
+
+class LinksPage extends StatefulWidget {
+  LinksPage({Key key, this.title}) : super(key: key);
+  final String title;
+
+  @override
+  _LinksPageState createState() => _LinksPageState();
+}
+
+class _LinksPageState extends State<LinksPage> {
+  Future<void> _launched;
+  String _phone = '';
+
+  Widget _launchStatus(BuildContext context, AsyncSnapshot<void> snapshot) {
+    if (snapshot.hasError) {
+      return Text('Error: ${snapshot.error}');
+    } else {
+      return const Text('');
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final Uri fullUri = Uri.parse('https://www.cylog.org/headers/');
+    final Uri routeName = Uri.parse('/url_launcher');
+
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(widget.title),
+      ),
+      body: ListView(
+        children: <Widget>[
+          Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              Padding(
+                padding: const EdgeInsets.all(16.0),
+                child: TextField(
+                    onChanged: (String text) => setState(() {
+                          _phone = text;
+                        }),
+                    decoration: const InputDecoration(
+                        hintText: 'Input the phone number to launch')),
+              ),
+              Link(
+                uri: Uri.parse('tel:$_phone'),
+                builder: (BuildContext context, FollowLink followLink) =>
+                    RaisedButton(
+                  onPressed: followLink,
+                  child: const Text('Make phone call'),
+                ),
+              ),
+              Padding(
+                padding: EdgeInsets.only(top: 32.0, bottom: 16.0),
+                child: Text('fullUri: $fullUri'),
+              ),
+              Link(
+                uri: fullUri,
+                target: LinkTarget.blank,
+                builder: (BuildContext context, FollowLink followLink) {
+                  return RaisedButton(
+                    onPressed: () => setState(() {
+                      _launched = followLink();
+                    }),
+                    child: const Text('Launch in blank'),
+                  );
+                },
+              ),
+              const Padding(padding: EdgeInsets.all(16.0)),
+              Link(
+                uri: fullUri,
+                target: LinkTarget.self,
+                builder: (BuildContext context, FollowLink followLink) {
+                  return RaisedButton(
+                    onPressed: () => setState(() {
+                      _launched = followLink();
+                    }),
+                    child: const Text('Launch in self'),
+                  );
+                },
+              ),
+              Padding(
+                padding: EdgeInsets.only(top: 32.0, bottom: 16.0),
+                child: Text('routeName: $routeName'),
+              ),
+              Link(
+                uri: routeName,
+                target: LinkTarget.blank,
+                builder: (BuildContext context, FollowLink followLink) {
+                  return RaisedButton(
+                    onPressed: () => setState(() {
+                      _launched = followLink();
+                    }),
+                    child: Text('Push in blank'),
+                  );
+                },
+              ),
+              const Padding(padding: EdgeInsets.all(16.0)),
+              Link(
+                uri: routeName,
+                target: LinkTarget.self,
+                builder: (BuildContext context, FollowLink followLink) {
+                  return RaisedButton(
+                    onPressed: () => setState(() {
+                      _launched = followLink();
+                    }),
+                    child: Text('Push in self'),
+                  );
+                },
+              ),
+              const Padding(padding: EdgeInsets.all(16.0)),
+              Link(
+                uri: null,
+                builder: (BuildContext context, FollowLink followLink) {
+                  return RaisedButton(
+                    onPressed: followLink,
+                    child: Text('Disabled'),
+                  );
+                },
+              ),
+              const Padding(padding: EdgeInsets.all(16.0)),
+              FutureBuilder<void>(future: _launched, builder: _launchStatus),
+            ],
+          ),
+        ],
+      ),
+    );
+  }
+}

packages/url_launcher/url_launcher/lib/url_launcher.dart

@@ -9,6 +9,9 @@ import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 import 'package:url_launcher_platform_interface/url_launcher_platform_interface.dart';
 
+export 'package:url_launcher_platform_interface/link.dart'
+    show Link, LinkTarget, LinkWidgetBuilder, FollowLink;
+
 /// Parses the specified URL string and delegates handling of it to the
 /// underlying platform.
 ///

packages/url_launcher/url_launcher_platform_interface/lib/link.dart

@@ -0,0 +1,133 @@
+// Copyright 2017 The Chromium 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 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+
+/// Signature for a function provided by the [Link] widget that instructs it to
+/// follow the link.
+typedef FollowLink = Future<void> Function();
+
+/// Signature for a builder function passed to the [Link] widget to construct
+/// the widget tree under it.
+typedef LinkWidgetBuilder = Widget Function(
+  BuildContext context,
+  FollowLink followLink,
+);
+
+/// Signature for a delegate function to build the [Link] widget.
+typedef LinkDelegate = Widget Function(Link linkWidget);
+
+/// Defines where a Link URL should be open.
+///
+/// This is a class instead of an enum to allow future customizability e.g.
+/// opening a link in a specific iframe.
+class LinkTarget {
+  /// Const private constructor with a [debugLabel] to allow the creation of
+  /// multiple distinct const instances.
+  const LinkTarget._({this.debugLabel});
+
+  /// Used to distinguish multiple const instances of [LinkTarget].
+  final String debugLabel;
+
+  /// Use the default target for each platform.
+  ///
+  /// On Android, the default is [blank]. On the web, the default is [self].
+  ///
+  /// iOS, on the other hand, defaults to [self] for web URLs, and [blank] for
+  /// non-web URLs.
+  static const defaultTarget = LinkTarget._(debugLabel: 'defaultTarget');
+
+  /// On the web, this opens the link in the same tab where the flutter app is
+  /// running.
+  ///
+  /// On Android and iOS, this opens the link in a webview within the app.
+  static const self = LinkTarget._(debugLabel: 'self');
+
+  /// On the web, this opens the link in a new tab or window (depending on the
+  /// browser and user configuration).
+  ///
+  /// On Android and iOS, this opens the link in the browser or the relevant
+  /// app.
+  static const blank = LinkTarget._(debugLabel: 'blank');
+}
+
+/// Used to override the delegate that builds the link.
+set linkDelegate(LinkDelegate delegate) {
+  Link._linkDelegate = delegate;
+}
+
+/// A widget that renders a real link on the web, and uses WebViews in native
+/// platforms to open links.
+///
+/// Example link to an external URL:
+///
+/// ```dart
+/// Link(
+///   uri: Uri.parse('https://flutter.dev'),
+///   builder: (BuildContext context, FollowLink followLink) => RaisedButton(
+///     onPressed: followLink,
+///     // ... other properties here ...
+///   )},
+/// );
+/// ```
+///
+/// Example link to a route name within the app:
+///
+/// ```dart
+/// Link(
+///   uri: Uri.parse('/home'),
+///   builder: (BuildContext context, FollowLink followLink) => RaisedButton(
+///     onPressed: followLink,
+///     // ... other properties here ...
+///   )},
+/// );
+/// ```
+class Link extends StatelessWidget {
+  /// Called at build time to construct the widget tree under the link.
+  final LinkWidgetBuilder builder;
+
+  /// The destination that this link leads to.
+  final Uri uri;
+
+  /// The target indicating where to open the link.
+  final LinkTarget target;
+
+  /// Whether the link is disabled or not.
+  bool get isDisabled => uri == null;
+
+  static LinkDelegate _linkDelegate = (Link link) => _DefaultLinkDelegate(link);
+
+  /// Creates a widget that renders a real link on the web, and uses WebViews in
+  /// native platforms to open links.
+  Link({
+    Key key,
+    @required this.uri,
+    LinkTarget target,
+    @required this.builder,
+  })  : target = target ?? LinkTarget.defaultTarget,
+        super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return _linkDelegate(this);
+  }
+}
+
+class _DefaultLinkDelegate extends StatelessWidget {
+  const _DefaultLinkDelegate(this.link);
+
+  final Link link;
+
+  Future<void> _followLink() {
+    // The default link delegate uses url launcher to open URIs.
+    // TODO(mdebbar): use url_launcher.
+    return Future<void>.value(null);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return link.builder(context, link.isDisabled ? null : _followLink);
+  }
+}