Complete example

- Update code
- Add docs

packages/stream_chat_flutter_core/example/lib/main.dart

@@ -28,19 +28,31 @@ Future<void> main() async {
   );
 }
 
+/// Example application using Stream Chat core widgets.
+/// Stream Chat Core is a set of Flutter wrappers which provide basic functionality
+/// for building Flutter applications using Stream.
+/// If you'd prefer using pre-made UI widgets for your app, please see our other
+/// package, `stream_chat_flutter`.
 class StreamExample extends StatelessWidget {
+  /// Minimal example using Stream's core Flutter package.
+  /// If you'd prefer using pre-made UI widgets for your app, please see our other
+  /// package, `stream_chat_flutter`.
   const StreamExample({
     Key key,
     @required this.client,
   }) : super(key: key);
 
+  /// Instance of Stream Client.
+  /// Stream's [Client] can be used to connect to our servers and set the default
+  /// user for the application. Performing these actions trigger a websocket connection
+  /// allowing for real-time updates.
   final Client client;
 
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
-      title: 'Stream Chat Dart Example',
+      title: 'Stream Chat Core Example',
-      home: _HomeScreen(),
+      home: HomeScreen(),
       builder: (context, child) => StreamChatCore(
         client: client,
         child: ChannelsBloc(child: child),
@@ -49,7 +61,12 @@ class StreamExample extends StatelessWidget {
   }
 }
 
-class _HomeScreen extends StatelessWidget {
+/// Basic layout displaying a list of [Channel]s the user is a part of.
+/// This is implemented using [ChannelListCore].
+///
+/// [ChannelListCore] is a `builder` with callbacks for constructing UIs based
+/// on different scenarios.
+class HomeScreen extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -81,15 +98,21 @@ class _HomeScreen extends StatelessWidget {
             ListView.builder(
           itemCount: channels.length,
           itemBuilder: (BuildContext context, int index) {
-            final item = channels[index];
+            final _item = channels[index];
             return ListTile(
-              title: Text(item.name),
+              title: Text(_item.name),
-              subtitle: Text(item.state.lastMessage.text),
+              subtitle: Text(_item.state.lastMessage.text),
               onTap: () {
+                /// Display a list of messages when the user taps on an item.
+                /// We can use [StreamChannel] to wrap our [MessageScreen] screen
+                /// with the selected channel.
+                ///
+                /// This allows us to use a built-in inherited widget for accessing
+                /// our `channel` later on.
                 Navigator.of(context).push(
                   MaterialPageRoute(
                     builder: (context) => StreamChannel(
-                      channel: item,
+                      channel: _item,
                       child: MessageScreen(),
                     ),
                   ),
@@ -103,6 +126,12 @@ class _HomeScreen extends StatelessWidget {
   }
 }
 
+/// A list of messages sent in the current channel.
+/// When a user taps on a channel in [HomeScreen], a navigator push [MessageScreen]
+/// to display the list of messages in the selected channel.
+///
+/// This is implemented using [MessageListCore], a convenience builder with
+/// callbacks for building UIs based on different api results.
 class MessageScreen extends StatefulWidget {
   @override
   _MessageScreenState createState() => _MessageScreenState();
@@ -136,8 +165,15 @@ class _MessageScreenState extends State<MessageScreen> {
 
   @override
   Widget build(BuildContext context) {
+    /// To access the current channel, we can use the `.of()` method on [StreamChannel]
+    /// to fetch the closest instance.
+    final channel = StreamChannel.of(context).channel;
     return Scaffold(
-      body: Column(
+      appBar: AppBar(
+        title: Text(channel.name),
+      ),
+      body: SafeArea(
+        child: Column(
           children: [
             Expanded(
               child: MessageListCore(
@@ -155,8 +191,10 @@ class _MessageScreenState extends State<MessageScreen> {
                     ),
                   );
                 },
-              messageListBuilder:
+                messageListBuilder: (
-                  (BuildContext context, List<Message> messages) {
+                  BuildContext context,
+                  List<Message> messages,
+                ) {
                   return ListView.builder(
                     controller: _scrollController,
                     itemCount: messages.length,
@@ -205,10 +243,9 @@ class _MessageScreenState extends State<MessageScreen> {
                     child: InkWell(
                       onTap: () async {
                         if (_controller.value.text.isNotEmpty) {
-                        //TODO(Nash): Send Message
+                          await channel.sendMessage(
-                        // await widget.channel.sendMessage(
+                            Message(text: _controller.value.text),
-                        //   Message(text: _controller.value.text),
+                          );
-                        // );
                           _controller.clear();
                           _updateList();
                         }
@@ -229,15 +266,20 @@ class _MessageScreenState extends State<MessageScreen> {
             )
           ],
         ),
+      ),
     );
   }
 }
 
+/// Extensions can be used to add functionality to the SDK. In the examples
+/// below, we add two simple extensions to the [Client] and [Channel].
 extension on Client {
+  /// Fetches the current user id.
   String get uid => state.user.id;
 }
 
 extension on Channel {
+  /// Fetches the name of the channel by accessing [extraData] or [cid].
   String get name {
     final _channelName = extraData['name'];
     if (_channelName != null) {