fix for #12

Wrapped the TextField in a LimitedBox, gavethe MessageInput a new property for that which defaults to 150p

lib/src/message_input.dart

@@ -56,12 +56,13 @@ import 'stream_channel.dart';
 /// The widget renders the ui based on the first ancestor of type [StreamChatTheme].
 /// Modify it to change the widget appearance.
 class MessageInput extends StatefulWidget {
-  MessageInput({
-    Key key,
+  MessageInput(
+      {Key key,
       this.onMessageSent,
       this.parentMessage,
       this.editMessage,
-  }) : super(key: key);
+      this.maxHeight = 150})
+      : super(key: key);
 
   /// Message to edit
   final Message editMessage;
@@ -72,6 +73,9 @@ class MessageInput extends StatefulWidget {
   /// Parent message in case of a thread
   final Message parentMessage;
 
+  /// Maximum Height for the TextField to grow before it starts scrolling
+  final double maxHeight;
+
   @override
   _MessageInputState createState() => _MessageInputState();
 }
@@ -111,6 +115,7 @@ class _MessageInputState extends State<MessageInput> {
   Flex _buildTextField(BuildContext context) {
     return Flex(
       direction: Axis.horizontal,
+      crossAxisAlignment: CrossAxisAlignment.end,
       children: <Widget>[
         _buildAttachmentButton(),
         _buildTextInput(context),
@@ -133,6 +138,8 @@ class _MessageInputState extends State<MessageInput> {
 
   Expanded _buildTextInput(BuildContext context) {
     return Expanded(
+      child: LimitedBox(
+        maxHeight: widget.maxHeight,
         child: TextField(
           key: Key('messageInputText'),
           minLines: null,
@@ -183,6 +190,7 @@ class _MessageInputState extends State<MessageInput> {
             border: InputBorder.none,
           ),
         ),
+      ),
     );
   }