implements a ctor

BookAStar/BookAStar/Pages/EstimatePages/BookQueriesPage.xaml.cs

@@ -14,14 +14,28 @@ namespace BookAStar.Pages
         public BookQueriesPage()
         {
             InitializeComponent();
-            var model = new BookQueriesViewModel();
+            BindingContext = new BookQueriesViewModel();
+        }
+
+        public BookQueriesPage(BookQueriesViewModel model)
+        {
+            InitializeComponent();
+            BindingContext = model;
+        }
+
+        protected override void OnBindingContextChanged()
+        {
+            BookQueriesViewModel model = (BookQueriesViewModel) BindingContext;
+            if (model!=null)
+            {
                 model.RefreshQueries =
-                new Command( () => {
+                    new Command(() =>
+                    {
                         DataManager.Instance.BookQueries.Execute(null);
                         this.list.EndRefresh();
                     });
-            
+            }
-            BindingContext = model;
+            base.OnBindingContextChanged();
         }
 
         private void OnViewDetail(object sender, ItemTappedEventArgs e)