Added InverseTrigger and matching sample

src/TestApp/MainPage.xaml

@@ -31,6 +31,10 @@
 				<local:SampleContainer Title="IsNullOrEmptyStateTrigger">
 					<samples:IsNullOrEmptySample />
 				</local:SampleContainer>
+
+                <local:SampleContainer Title="InverseTrigger">
+                    <samples:InverseSample />
+                </local:SampleContainer>
 
 				<local:SampleContainer Title="IsTypePresentStateTrigger">
 					<samples:IsTypePresentSample />

src/TestApp/Samples/InverseSample.xaml

@@ -0,0 +1,114 @@
+<UserControl x:Class="TestApp.Samples.InverseSample"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="using:TestApp.Samples"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:triggers="using:WindowsStateTriggers"
+             mc:Ignorable="d">
+    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
+        <VisualStateManager.VisualStateGroups>
+            <VisualStateGroup x:Name="textboxstates">
+                <VisualState x:Name="textboxnotemptystate">
+                    <VisualState.StateTriggers>
+                        <triggers:InverseTrigger>
+                            <triggers:InverseTrigger.StateTrigger>
+                                <triggers:IsNullOrEmptyStateTrigger Value="{x:Bind textbox.Text, Mode=OneWay}" />
+                            </triggers:InverseTrigger.StateTrigger>
+                        </triggers:InverseTrigger>
+                    </VisualState.StateTriggers>
+                    <VisualState.Setters>
+                        <Setter Target="textbox.BorderBrush"
+                                Value="Green" />
+                    </VisualState.Setters>
+                </VisualState>
+                <VisualState x:Name="textboxemptystate">
+                    <VisualState.StateTriggers>
+                        <triggers:IsNullOrEmptyStateTrigger Value="{x:Bind textbox.Text, Mode=OneWay}" />
+                    </VisualState.StateTriggers>
+                    <VisualState.Setters>
+                        <Setter Target="textbox.Background"
+                                Value="BlanchedAlmond" />
+                        <Setter Target="textbox.BorderBrush"
+                                Value="Red" />
+                        <Setter Target="textboxError.Visibility"
+                                Value="Visible" />
+                    </VisualState.Setters>
+                </VisualState>
+            </VisualStateGroup>
+            <VisualStateGroup x:Name="listboxstates">
+                <VisualState x:Name="listnotemptystate">
+                    <VisualState.StateTriggers>
+                        <triggers:InverseTrigger>
+                            <triggers:InverseTrigger.StateTrigger>
+                                <triggers:IsNullOrEmptyStateTrigger Value="{x:Bind list.Items, Mode=OneWay}" />
+                            </triggers:InverseTrigger.StateTrigger>
+                        </triggers:InverseTrigger>
+                    </VisualState.StateTriggers>
+                    <VisualState.Setters>
+                        <Setter Target="list.Visibility"
+                                Value="Visible" />
+                    </VisualState.Setters>
+                </VisualState>
+                <VisualState x:Name="listemptystate">
+                    <VisualState.StateTriggers>
+                        <triggers:IsNullOrEmptyStateTrigger Value="{x:Bind list.Items, Mode=OneWay}" />
+                    </VisualState.StateTriggers>
+                    <VisualState.Setters>
+                        <Setter Target="remove.IsEnabled"
+                                Value="False" />
+                        <Setter Target="listEmptyMessage.Visibility"
+                                Value="Visible" />
+                    </VisualState.Setters>
+                </VisualState>
+            </VisualStateGroup>
+        </VisualStateManager.VisualStateGroups>
+        <StackPanel VerticalAlignment="Center">
+            <TextBlock Text="The TextBox will be green if not empty." />
+            <StackPanel Orientation="Horizontal"
+                        Margin="0 0 0 20">
+                <TextBox x:Name="textbox"
+                         Text=""
+                         Width="200" />
+                <TextBlock x:Name="textboxError"
+                           Text="* Required"
+                           Foreground="Red"
+                           Margin="10 0 0 0"
+                           Visibility="Collapsed" />
+            </StackPanel>
+            <StackPanel Orientation="Horizontal">
+                <Button x:Name="add"
+                        Content="Add"
+                        Margin="0 0 10 0"
+                        Click="add_Click" />
+                <Button x:Name="remove"
+                        Content="Remove"
+                        Click="remove_Click" />
+            </StackPanel>
+            <TextBlock x:Name="listEmptyMessage"
+                       Text="List is empty, add some items"
+                       Visibility="Collapsed" />
+            <ListBox x:Name="list"
+                     HorizontalAlignment="Left"
+                     Visibility="Collapsed">
+                <ListBox.ItemsPanel>
+                    <ItemsPanelTemplate>
+                        <StackPanel Orientation="Horizontal" />
+                    </ItemsPanelTemplate>
+                </ListBox.ItemsPanel>
+                <ListBox.ItemContainerStyle>
+                    <Style TargetType="ListBoxItem">
+                        <Setter Property="Padding"
+                                Value="3" />
+                        <Setter Property="Margin"
+                                Value="3" />
+                        <Setter Property="Background"
+                                Value="Red" />
+                        <Setter Property="Foreground"
+                                Value="White" />
+                    </Style>
+                </ListBox.ItemContainerStyle>
+            </ListBox>
+        </StackPanel>
+    </Grid>
+</UserControl>

src/TestApp/Samples/InverseSample.xaml.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+
+// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234238
+
+namespace TestApp.Samples
+{
+	/// <summary>
+	/// An empty page that can be used on its own or navigated to within a Frame.
+	/// </summary>
+	public sealed partial class InverseSample : UserControl
+	{
+		public InverseSample()
+		{
+			this.InitializeComponent();
+		}
+
+		private void add_Click(object sender, RoutedEventArgs e)
+		{
+			list.Items.Add("Item");
+		}
+
+		private void remove_Click(object sender, RoutedEventArgs e)
+		{
+			list.Items.RemoveAt(0);
+		}
+	}
+}

src/TestApp/Samples/IsNullOrEmptySample.xaml

@@ -13,8 +13,13 @@
 		<VisualStateManager.VisualStateGroups>
 
 			<VisualStateGroup x:Name="textboxstates">
-				<VisualState x:Name="textboxnotemptystate" />
-				<VisualState x:Name="textboxemptystate">
+                <VisualState x:Name="textboxnotemptystate">
+                    <VisualState.Setters>
+                        <Setter Target="textbox.BorderBrush"
+                                Value="Green" />
+                    </VisualState.Setters>
+                </VisualState>
+                <VisualState x:Name="textboxemptystate">
 					<VisualState.StateTriggers>
 						<triggers:IsNullOrEmptyStateTrigger Value="{x:Bind textbox.Text, Mode=OneWay}"/>
 					</VisualState.StateTriggers>

src/TestApp/TestApp.csproj

@@ -106,6 +106,9 @@
     <Compile Include="Samples\IsHostedSample.xaml.cs">
       <DependentUpon>IsHostedSample.xaml</DependentUpon>
     </Compile>
+    <Compile Include="Samples\InverseSample.xaml.cs">
+      <DependentUpon>InverseSample.xaml</DependentUpon>
+    </Compile>
     <Compile Include="Samples\IsNullOrEmptySample.xaml.cs">
       <DependentUpon>IsNullOrEmptySample.xaml</DependentUpon>
     </Compile>
@@ -186,6 +189,10 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
+    <Page Include="Samples\InverseSample.xaml">
+      <Generator>MSBuild:Compile</Generator>
+      <SubType>Designer</SubType>
+    </Page>
     <Page Include="Samples\IsNullOrEmptySample.xaml">
       <Generator>MSBuild:Compile</Generator>
       <SubType>Designer</SubType>

src/WindowsStateTriggers/InverseTrigger.cs

@@ -0,0 +1,81 @@
+// Copyright (c) Morten Nielsen. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Windows.UI.Xaml;
+
+namespace WindowsStateTriggers
+{
+    /// <summary>
+    /// Inverts another State Trigger that is using ITriggerValue
+    /// </summary>
+    public class InverseTrigger : StateTriggerBase, ITriggerValue
+    {
+        /// <summary>
+        /// Gets or sets the State Trigger to invert.
+        /// </summary>
+        public ITriggerValue StateTrigger
+        {
+            get { return (ITriggerValue)GetValue(StateTriggerProperty); }
+            set { SetValue(StateTriggerProperty, value); }
+        }
+
+        /// <summary>
+        /// Identifies the <see cref="StateTrigger"/> DependencyProperty
+        /// </summary>
+        public static readonly DependencyProperty StateTriggerProperty =
+            DependencyProperty.Register("StateTrigger", typeof(ITriggerValue), typeof(InverseTrigger),
+            new PropertyMetadata(null, OnStateTriggerPropertyChanged));
+
+        private static void OnStateTriggerPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+        {
+            var obj = (InverseTrigger)d;
+            var val = (ITriggerValue)e.NewValue;
+            if (val != null)
+            {
+                obj.IsActive = !val.IsActive;
+                WeakEventListener<ITriggerValue, object, EventArgs> weakEvent = new WeakEventListener<ITriggerValue, object, EventArgs>(val)
+                {
+                    OnEventAction = (instance, source, args) => obj.IsActive = !instance.IsActive,
+                    OnDetachAction = (instance, weakEventListener) => instance.IsActiveChanged -= weakEventListener.OnEvent
+                };
+                val.IsActiveChanged += weakEvent.OnEvent;
+            }
+            else
+            {
+                obj.IsActive = false;
+            }
+        }
+        #region ITriggerValue
+
+        private bool m_IsActive;
+
+        /// <summary>
+        /// Gets a value indicating whether this trigger is active.
+        /// </summary>
+        /// <value><c>true</c> if this trigger is active; otherwise, <c>false</c>.</value>
+        public bool IsActive
+        {
+            get { return m_IsActive; }
+            private set
+            {
+                if (m_IsActive != value)
+                {
+                    m_IsActive = value;
+                    base.SetActive(value);
+                    if (IsActiveChanged != null)
+                        IsActiveChanged(this, EventArgs.Empty);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Occurs when the <see cref="IsActive" /> property has changed.
+        /// </summary>
+        public event EventHandler IsActiveChanged;
+
+        #endregion ITriggerValue
+    }
+}

src/WindowsStateTriggers/WindowsStateTriggers.csproj

@@ -126,6 +126,7 @@
     <Compile Include="CompositeStateTrigger.cs" />
     <Compile Include="FullScreenModeTrigger.cs" />
     <Compile Include="HostedStateTrigger.cs" />
+    <Compile Include="InverseTrigger.cs" />
     <Compile Include="UserHandPreferenceStateTrigger.cs" />
     <Compile Include="RegexStateTrigger.cs" />
     <Compile Include="InputTypeTrigger.cs" />