Make full-screen dialog text editable in gallery (#13690) (#15732)

Make the full-screen dialog text editable in gallery (#13690)

examples/flutter_gallery/lib/demo/material/full_screen_dialog_demo.dart

diff --git a/examples/flutter_gallery/lib/demo/material/full_screen_dialog_demo.dart b/examples/flutter_gallery/lib/demo/material/full_screen_dialog_demo.dart
index d44263b..91d5802 100644
--- a/examples/flutter_gallery/lib/demo/material/full_screen_dialog_demo.dart
+++ b/examples/flutter_gallery/lib/demo/material/full_screen_dialog_demo.dart
@@ -106,8 +106,12 @@
   DateTime _toDateTime = new DateTime.now();
   bool _allDayValue = false;
   bool _saveNeeded = false;
+  bool _hasLocation = false;
+  bool _hasName = false;
+  String _eventName;
 
   Future<bool> _onWillPop() async {
+    _saveNeeded = _hasLocation || _hasName || _saveNeeded;
     if (!_saveNeeded)
       return true;
 
@@ -147,7 +151,7 @@
 
     return new Scaffold(
       appBar: new AppBar(
-        title: const Text('New event'),
+        title: new Text(_hasName ? _eventName : 'Event Name TBD'),
         actions: <Widget> [
           new FlatButton(
             child: new Text('SAVE', style: theme.textTheme.body1.copyWith(color: Colors.white)),
@@ -164,19 +168,38 @@
           children: <Widget>[
             new Container(
               padding: const EdgeInsets.symmetric(vertical: 8.0),
-              decoration: new BoxDecoration(
-                border: new Border(bottom: new BorderSide(color: theme.dividerColor))
-              ),
               alignment: Alignment.bottomLeft,
-              child: new Text('Event name', style: theme.textTheme.display2)
+              child: new TextField(
+                decoration: const InputDecoration(
+                  labelText: 'Event name',
+                  filled: true
+                ),
+                style: theme.textTheme.headline,
+                onChanged: (String value) {
+                  setState(() {
+                    _hasName = value.isNotEmpty;
+                    if (_hasName) {
+                      _eventName = value;
+                    }
+                  });
+                }
+              )
             ),
             new Container(
               padding: const EdgeInsets.symmetric(vertical: 8.0),
-              decoration: new BoxDecoration(
-                border: new Border(bottom: new BorderSide(color: theme.dividerColor))
-              ),
               alignment: Alignment.bottomLeft,
-              child: new Text('Location', style: theme.textTheme.title.copyWith(color: Colors.black54))
+              child: new TextField(
+                decoration: const InputDecoration(
+                  labelText: 'Location',
+                  hintText: 'Where is the event?',
+                  filled: true
+                ),
+                onChanged: (String value) {
+                  setState(() {
+                    _hasLocation = value.isNotEmpty;
+                  });
+                }
+              )
             ),
             new Column(
               crossAxisAlignment: CrossAxisAlignment.start,