snackbar fix

Runtime/material/scaffold.cs

         Timer _snackBarTimer;
         bool _accessibleNavigation;
 
-        ScaffoldFeatureController<SnackBar, SnackBarClosedReason> showSnackBar(SnackBar snackbar) {
-            this._snackBarController = this._snackBarController ?? SnackBar.createAnimationController(vsync: this);
-            this._snackBarController.addStatusListener(this._handleSnackBarStatusChange);
+        public ScaffoldFeatureController<SnackBar, SnackBarClosedReason> showSnackBar(SnackBar snackbar) {
+            if (this._snackBarController == null) {
+                this._snackBarController = SnackBar.createAnimationController(vsync: this);
+                this._snackBarController.addStatusListener(this._handleSnackBarStatusChange);
+            }
+            
             if (this._snackBars.isEmpty()) {
                 D.assert(this._snackBarController.isDismissed);
                 this._snackBarController.forward();
         }
     }
 
-    class ScaffoldFeatureController<T, U> where T : Widget {
+    public class ScaffoldFeatureController<T, U> where T : Widget {
         public ScaffoldFeatureController(
             T _widget,
             Promise<U> _completer,

Samples/UIWidgetSample/MaterialSample.cs

                         crossAxisAlignment: CrossAxisAlignment.center,
                         children: new List<Widget> {
                             new Icon(this.choice.icon, size: 128.0f, color: textStyle.color),
-                            new Text(this.choice.title, style: textStyle)
+                            new RaisedButton(
+                                child: new Text(this.choice.title, style: textStyle),
+                                onPressed: () => {
+                                    SnackBar snackBar = new SnackBar(
+                                        content: new Text(this.choice.title + " is chosen !"),
+                                        action: new SnackBarAction(
+                                            label: "Ok",
+                                            onPressed: () => { }));
+
+                                    Scaffold.of(context).showSnackBar(snackBar);
+                                })
                         }
                     )
                 )