added a sticky sample

src/Elmish.WPF.sln

@@ -64,6 +64,10 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution
 		..\TUTORIAL.md = ..\TUTORIAL.md
 	EndProjectSection
 EndProject
+Project("{6EC3EE1D-3C4E-46DD-8F32-0CC8E7565705}") = "Sticky.Core", "Samples\Sticky.Core\Sticky.Core.fsproj", "{F251BEA3-6AD1-4C14-9F3D-87FCFA4292EB}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Sticky", "Samples\Sticky\Sticky.csproj", "{668E3AAD-B2AA-4934-804E-234C4F502038}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -174,6 +178,14 @@ Global
 		{F095E7E4-28ED-4223-A92F-4E86922E34EF}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{F095E7E4-28ED-4223-A92F-4E86922E34EF}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{F095E7E4-28ED-4223-A92F-4E86922E34EF}.Release|Any CPU.Build.0 = Release|Any CPU
+		{F251BEA3-6AD1-4C14-9F3D-87FCFA4292EB}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F251BEA3-6AD1-4C14-9F3D-87FCFA4292EB}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F251BEA3-6AD1-4C14-9F3D-87FCFA4292EB}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F251BEA3-6AD1-4C14-9F3D-87FCFA4292EB}.Release|Any CPU.Build.0 = Release|Any CPU
+		{668E3AAD-B2AA-4934-804E-234C4F502038}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{668E3AAD-B2AA-4934-804E-234C4F502038}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{668E3AAD-B2AA-4934-804E-234C4F502038}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{668E3AAD-B2AA-4934-804E-234C4F502038}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -203,6 +215,8 @@ Global
 		{36A4AEAF-8282-47EC-B751-BB3D16AB1A20} = {BBAFEB1E-93C0-4C7E-8E0A-026BB05C88EC}
 		{F66F6E21-357E-4CE8-9807-042C5171AB06} = {BBAFEB1E-93C0-4C7E-8E0A-026BB05C88EC}
 		{F095E7E4-28ED-4223-A92F-4E86922E34EF} = {BBAFEB1E-93C0-4C7E-8E0A-026BB05C88EC}
+		{F251BEA3-6AD1-4C14-9F3D-87FCFA4292EB} = {BBAFEB1E-93C0-4C7E-8E0A-026BB05C88EC}
+		{668E3AAD-B2AA-4934-804E-234C4F502038} = {BBAFEB1E-93C0-4C7E-8E0A-026BB05C88EC}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {3125D461-08F4-4071-AAE5-1038EF84A360}

src/Elmish.WPF/Binding.fs

@@ -866,7 +866,7 @@ module Binding =
     BindingData.subModelSelectedItemLast a.Data b.Data
 
   ///Creates a one-way binding with the model as the value.
-  let internal id<'model, 'msg when 'model : equality> : string -> Binding<'model, 'msg> =
+  let id<'model, 'msg when 'model : equality> : string -> Binding<'model, 'msg> =
     { Get = id }
     |> BindingData.OneWay.box
     |> OneWayData

src/Samples/Sticky.Core/Program.fs

@@ -0,0 +1,57 @@
+module Elmish.WPF.Samples.Sticky.Program
+
+open Serilog
+open Serilog.Extensions.Logging
+open Elmish.WPF
+
+type Model =
+  { Count: int
+    StepSize: int }
+
+type Msg =
+  | Increment
+  | Decrement
+  | SetStepSize of int
+  | Reset
+
+let init =
+  { Count = 0
+    StepSize = 1 }
+
+let canReset = (<>) init
+
+let update msg m =
+  match msg with
+  | Increment -> { m with Count = m.Count + m.StepSize }
+  | Decrement -> { m with Count = m.Count - m.StepSize }
+  | SetStepSize x -> { m with StepSize = x }
+  | Reset -> init
+
+let bindings () : Binding<Model, Msg> list = [
+  "CounterValue"
+    |> Binding.id
+    |> Binding.sticky (fun v -> v % 2 = 0)
+    |> Binding.mapModel (fun m -> m.Count)
+  "Increment" |> Binding.cmd Increment
+  "Decrement" |> Binding.cmd Decrement
+  "StepSize" |> Binding.twoWay(
+    (fun m -> float m.StepSize),
+    int >> SetStepSize)
+  "Reset" |> Binding.cmdIf(Reset, canReset)
+]
+
+let designVm = ViewModel.designInstance init (bindings ())
+
+let main window =
+
+  let logger =
+    LoggerConfiguration()
+      .MinimumLevel.Override("Elmish.WPF.Update", Events.LogEventLevel.Verbose)
+      .MinimumLevel.Override("Elmish.WPF.Bindings", Events.LogEventLevel.Verbose)
+      .MinimumLevel.Override("Elmish.WPF.Performance", Events.LogEventLevel.Verbose)
+      .WriteTo.Console()
+      .CreateLogger()
+
+  WpfProgram.mkSimple (fun () -> init) update bindings
+  |> WpfProgram.withLogger (new SerilogLoggerFactory(logger))
+  |> WpfProgram.startElmishLoop window

src/Samples/Sticky.Core/Sticky.Core.fsproj

@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net5.0-windows</TargetFramework>
+    <UseWpf>true</UseWpf>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="Program.fs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Serilog" Version="2.9.0" />
+    <PackageReference Include="Serilog.Extensions.Logging" Version="3.0.1" />
+    <PackageReference Include="Serilog.Sinks.Console" Version="3.1.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\Elmish.WPF\Elmish.WPF.fsproj" />
+  </ItemGroup>
+
+</Project>

src/Samples/Sticky/App.xaml

@@ -0,0 +1,7 @@
+<Application x:Class="Elmish.WPF.Samples.Sticky.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             StartupUri="MainWindow.xaml">
+  <Application.Resources>
+  </Application.Resources>
+</Application>

src/Samples/Sticky/App.xaml.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Windows;
+
+namespace Elmish.WPF.Samples.Sticky
+{
+  public partial class App : Application
+  {
+    public App()
+    {
+      this.Activated += StartElmish;
+    }
+
+    private void StartElmish(object sender, EventArgs e)
+    {
+      this.Activated -= StartElmish;
+      Program.main(MainWindow);
+    }
+
+  }
+}

src/Samples/Sticky/MainWindow.xaml

@@ -0,0 +1,24 @@
+<Window x:Class="Elmish.WPF.Samples.Sticky.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:vm="clr-namespace:Elmish.WPF.Samples.Sticky;assembly=Sticky.Core"
+        Title="Sticky"
+        Height="120"
+        Width="500"
+        WindowStartupLocation="CenterScreen"
+        mc:Ignorable="d"
+        d:DataContext="{x:Static vm:Program.designVm}">
+  <StackPanel Orientation="Vertical">
+    <TextBlock Text="The counter value binding is sticky to even numbers"/>
+    <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Top" Margin="0,25,0,0">
+      <TextBlock Text="{Binding CounterValue, StringFormat='Counter value: {0}'}" Width="110" Margin="0,5,10,5" />
+      <Button Command="{Binding Decrement}" Content="-" Margin="0,5,10,5" Width="30" />
+      <Button Command="{Binding Increment}" Content="+" Margin="0,5,10,5" Width="30" />
+      <TextBlock Text="{Binding StepSize, StringFormat='Step size: {0}'}" Width="70" Margin="0,5,10,5" />
+      <Slider Value="{Binding StepSize}" TickFrequency="1" Maximum="10" Minimum="1" IsSnapToTickEnabled="True" Width="100" Margin="0,5,10,5" />
+      <Button Command="{Binding Reset}" Content="Reset" Margin="0,5,10,5" Width="50" />
+    </StackPanel>
+  </StackPanel>
+</Window>

src/Samples/Sticky/MainWindow.xaml.cs

@@ -0,0 +1,11 @@
+using System.Windows;
+
+namespace Elmish.WPF.Samples.Sticky {
+    public partial class MainWindow : Window
+    {
+        public MainWindow()
+        {
+            InitializeComponent();
+        }
+    }
+}

src/Samples/Sticky/Sticky.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net5.0-windows</TargetFramework>
+    <UseWpf>true</UseWpf>
+    <OutputType>Exe</OutputType>
+    <DisableWinExeOutputInference>true</DisableWinExeOutputInference>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Sticky.Core\Sticky.Core.fsproj" />
+  </ItemGroup>
+
+</Project>