Initial commit

Author: XAML-Knight

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/ViewportBehavior/ViewportBehaviorPage.xaml

@@ -7,7 +7,7 @@
       xmlns:behaviors="using:Microsoft.Toolkit.Uwp.UI.Behaviors"
       mc:Ignorable="d">
     <Page.Resources>
-        <behaviors:ViewportBehavior x:Key="ViewportBehavior" />
+        <behaviors:ViewportBehavior x:Key="ViewportBehavior" IsAlwaysOn="True"/>
     </Page.Resources>
 
     <Grid>

Microsoft.Toolkit.Uwp.UI.Behaviors/Viewport/ViewportBehavior.Properties.cs

@@ -0,0 +1,19 @@
+using Windows.UI.Xaml;
+
+namespace Microsoft.Toolkit.Uwp.UI.Behaviors
+{
+    public partial class ViewportBehavior
+    {
+        public static readonly DependencyProperty IsAlwaysOnProperty =
+            DependencyProperty.Register(nameof(IsAlwaysOn), typeof(bool), typeof(ViewportBehavior), new PropertyMetadata(true));
+
+        /// <summary>
+        /// Gets or sets a value indicating whether this behavior will remain attached after the associated element enters the viewport. When false, the behavior will remove itself after entering.
+        /// </summary>
+        public bool IsAlwaysOn
+        {
+            get { return (bool)GetValue(IsAlwaysOnProperty); }
+            set { SetValue(IsAlwaysOnProperty, value); }
+        }
+    }
+}

Microsoft.Toolkit.Uwp.UI.Behaviors/Viewport/ViewportBehavior.cs

@@ -14,7 +14,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Behaviors
     /// <summary>
     /// A class for listening element enter or exit the ScrollViewer viewport
     /// </summary>
-    public class ViewportBehavior : BehaviorBase<FrameworkElement>
+    public partial class ViewportBehavior : BehaviorBase<FrameworkElement>
     {
         /// <summary>
         /// The ScrollViewer hosting this element.
@@ -36,8 +36,8 @@ public class ViewportBehavior : BehaviorBase<FrameworkElement>
         /// <summary>
         /// The IsAlwaysOn value of the associated element
         /// </summary>
-        public static readonly DependencyProperty IsAlwaysOnProperty =
-            DependencyProperty.Register(nameof(IsAlwaysOn), typeof(bool), typeof(ViewportBehavior), new PropertyMetadata(default(bool)));
+        //public static readonly DependencyProperty IsAlwaysOnProperty =
+        //    DependencyProperty.Register(nameof(IsAlwaysOn), typeof(bool), typeof(ViewportBehavior), new PropertyMetadata(true));
 
         /// <summary>
         /// Associated element fully enter the ScrollViewer viewport event
@@ -59,14 +59,14 @@ public class ViewportBehavior : BehaviorBase<FrameworkElement>
         /// </summary>
         public event EventHandler ExitingViewport;
 
-        /// <summary>
-        /// Gets or sets a value indicating whether this behavior will remain attached after the associated element enters the viewport. When false, the behavior will remove itself after entering.
-        /// </summary>
-        public bool IsAlwaysOn
-        {
-            get { return (bool)GetValue(IsAlwaysOnProperty); }
-            set { SetValue(IsAlwaysOnProperty, value); }
-        }
+        ///// <summary>
+        ///// Gets or sets a value indicating whether this behavior will remain attached after the associated element enters the viewport. When false, the behavior will remove itself after entering.
+        ///// </summary>
+        //public bool IsAlwaysOn
+        //{
+        //    get { return (bool)GetValue(IsAlwaysOnProperty); }
+        //    set { SetValue(IsAlwaysOnProperty, value); }
+        //}
 
         /// <summary>
         /// Gets a value indicating whether associated element is fully in the ScrollViewer viewport