From 4ef5dd9430a5096702f7e965fd74a672059c34e0 Mon Sep 17 00:00:00 2001
From: Markus Ewald <cygon@nuclex.org>
Date: Wed, 6 Feb 2019 07:00:27 +0000
Subject: [PATCH] Cleaned and added a base class for view models with
 background processing tha uses the new ThreadedAction class to do its
 background processing; added a view binding interface for WinForms that
 emulates the WPF design

git-svn-id: file:///srv/devel/repo-conversion/nuwi@41 d2e56fa2-650e-0410-a79f-9358c0239efd
---
 Nuclex.Windows.Forms (net-4.0).csproj       |  12 +
 Source/ViewModels/ThreadedViewModel.Test.cs | 208 +++++++++++++++++
 Source/ViewModels/ThreadedViewModel.cs      | 243 ++++++++++++++++++++
 Source/Views/IView.cs                       |  37 +++
 Source/Views/ViewControl.cs                 |  87 +++++++
 Source/Views/ViewForm.cs                    |  87 +++++++
 6 files changed, 674 insertions(+)
 create mode 100644 Source/ViewModels/ThreadedViewModel.Test.cs
 create mode 100644 Source/ViewModels/ThreadedViewModel.cs
 create mode 100644 Source/Views/IView.cs
 create mode 100644 Source/Views/ViewControl.cs
 create mode 100644 Source/Views/ViewForm.cs

diff --git a/Nuclex.Windows.Forms (net-4.0).csproj b/Nuclex.Windows.Forms (net-4.0).csproj
index e52bd25..b77720e 100644
--- a/Nuclex.Windows.Forms (net-4.0).csproj	
+++ b/Nuclex.Windows.Forms (net-4.0).csproj	
@@ -55,6 +55,17 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="Source\ViewModels\ThreadedViewModel.cs" />
+    <Compile Include="Source\ViewModels\ThreadedViewModel.Test.cs">
+      <DependentUpon>ThreadedViewModel.cs</DependentUpon>
+    </Compile>
+    <Compile Include="Source\Views\IView.cs" />
+    <Compile Include="Source\Views\ViewControl.cs">
+      <SubType>UserControl</SubType>
+    </Compile>
+    <Compile Include="Source\Views\ViewForm.cs">
+      <SubType>Form</SubType>
+    </Compile>
     <EmbeddedResource Include="Source\ProgressReporter\ProgressReporterForm.resx">
       <DependentUpon>ProgressReporterForm.cs</DependentUpon>
       <SubType>Designer</SubType>
@@ -109,6 +120,7 @@
       <Link>Foundation.snk</Link>
     </None>
   </ItemGroup>
+  <ItemGroup />
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
diff --git a/Source/ViewModels/ThreadedViewModel.Test.cs b/Source/ViewModels/ThreadedViewModel.Test.cs
new file mode 100644
index 0000000..902886e
--- /dev/null
+++ b/Source/ViewModels/ThreadedViewModel.Test.cs
@@ -0,0 +1,208 @@
+#if UNITTEST
+
+using System;
+using System.ComponentModel;
+using System.Threading;
+using NUnit.Framework;
+
+namespace Nuclex.Windows.Forms.ViewModels {
+
+  /// <summary>Unit test for the threaded view model base class</summary>
+  [TestFixture]
+  public class ThreadedViewModelTest {
+
+    #region class DummyContext
+
+    /// <summary>Synchronization context that does absolutely nothing</summary>
+    private class DummyContext : ISynchronizeInvoke {
+
+      #region class SimpleAsyncResult
+
+      /// <summary>Barebones implementation of an asynchronous result</summary>
+      private class SimpleAsyncResult : IAsyncResult {
+
+        /// <summary>Ehether the asynchronous operation is complete</summary>
+        /// <remarks>
+        ///   Always true because it completes synchronously
+        /// </remarks>
+        public bool IsCompleted { get { return true; } }
+
+        /// <summary>
+        ///   Wait handle that can be used to wait for the asynchronous operation
+        /// </summary>
+        public WaitHandle AsyncWaitHandle {
+          get { throw new NotImplementedException("Not implemented"); }
+        }
+
+        /// <summary>Custom state that can be used to pass information around</summary>
+        public object AsyncState {
+          get { throw new NotImplementedException("Not implemented"); }
+        }
+
+        /// <summary>Whether the asynchronous operation completed synchronously</summary>
+        public bool CompletedSynchronously { get { return true; } }
+
+        /// <summary>The value returned from the asynchronous operation</summary>
+        public object ReturnedValue;
+
+      }
+
+      #endregion // class SimpleAsyncResult
+
+      /// <summary>Whether the calling thread needs to use Invoke()</summary>
+      public bool InvokeRequired {
+        get { return true; }
+      }
+
+      /// <summary>Schedules the specified method for execution in the target thread</summary>
+      /// <param name="method">Method the target thread will execute when it is idle</param>
+      /// <param name="arguments">Arguments that will be passed to the method</param>
+      /// <returns>
+      ///   An asynchronous result handle that can be used to check on the status of
+      ///   the call and wait for its completion
+      /// </returns>
+      public IAsyncResult BeginInvoke(Delegate method, object[] arguments) {
+        var asyncResult = new SimpleAsyncResult();
+        asyncResult.ReturnedValue = method.Method.Invoke(method.Target, arguments);
+        return asyncResult;
+      }
+
+      /// <summary>Waits for the asychronous call to complete</summary>
+      /// <param name="result">
+      ///   Asynchronous result handle returned by the <see cref="BeginInvoke" /> method
+      /// </param>
+      /// <returns>The original result returned by the asychronously called method</returns>
+      public object EndInvoke(IAsyncResult result) {
+        return ((SimpleAsyncResult)result).ReturnedValue;
+      }
+
+      /// <summary>
+      ///   Schedules the specified method for execution in the target thread and waits
+      ///   for it to complete
+      /// </summary>
+      /// <param name="method">Method that will be executed by the target thread</param>
+      /// <param name="arguments">Arguments that will be passed to the method</param>
+      /// <returns>The result returned by the specified method</returns>
+      public object Invoke(Delegate method, object[] arguments) {
+        return method.Method.Invoke(method.Target, arguments);
+      }
+
+    }
+
+    #endregion // class DummyContext
+
+    #region class TestViewModel
+
+    /// <summary>View model used to unit test the threaded view model base class</summary>
+    private class TestViewModel : ThreadedViewModel {
+
+      /// <summary>
+      ///   Initializes a new view model, letting the base class figure out the UI thread
+      /// </summary>
+      public TestViewModel() : base() {
+        this.finishedGate = new ManualResetEvent(initialState: false);
+      }
+
+      /// <summary>
+      ///   Initializes a new view model, using the specified context for the UI thread
+      /// </summary>
+      /// <param name="uiContext">Synchronization context of the UI thread</param>
+      public TestViewModel(ISynchronizeInvoke uiContext) : base(uiContext) {
+        this.finishedGate = new ManualResetEvent(initialState: false);
+      }
+
+      /// <summary>Immediately releases all resources owned by the instance</summary>
+      public override void Dispose() {
+        base.Dispose();
+
+        if(this.finishedGate != null) {
+          this.finishedGate.Dispose();
+          this.finishedGate = null;
+        }
+      }
+
+      /// <summary>Waits until the first background operation is finished</summary>
+      /// <returns>
+      ///   True if the background operation is finished, false if it is ongoing
+      /// </returns>
+      public bool WaitUntilFinished() {
+        return this.finishedGate.WaitOne(100);
+      }
+
+      /// <summary>Runs a background process that causes the specified error</summary>
+      /// <param name="error">Error that will be caused in the background process</param>
+      public void CauseErrorInBackgroundThread(Exception error) {
+        RunInBackground(() => throw error);
+      }
+
+      /// <summary>Last error that was reported by the threaded view model</summary>
+      public Exception ReportedError {
+        get { return this.reportedError; }
+      }
+
+      /// <summary>Called when an error occurs in the background thread</summary>
+      /// <param name="exception">Exception that was thrown in the background thread</param>
+      protected override void ReportError(Exception exception) {
+        this.reportedError = exception;
+        this.finishedGate.Set();
+      }
+
+      /// <summary>Last error that was reported by the threaded view model</summary>
+      private Exception reportedError;
+      /// <summary>Triggered when the </summary>
+      private ManualResetEvent finishedGate;
+
+    }
+
+    #endregion // class TestViewModel
+
+    /// <summary>Verifies that the threaded view model has a default constructor</summary>
+    [Test]
+    public void HasDefaultConstructor() {
+      using(var mainForm = new System.Windows.Forms.Form()) {
+        mainForm.Show();
+        try {
+          mainForm.Visible = false;
+          using(new TestViewModel()) { }
+        }
+        finally {
+          mainForm.Close();
+        }
+      }
+    }
+
+    /// <summary>
+    ///   Verifies that the threaded view model can be constructed with a custom UI context
+    /// </summary>
+    [Test]
+    public void HasCustomSychronizationContextConstructor() {
+      using(new TestViewModel(new DummyContext())) { }
+    }
+
+    /// <summary>Checks that a new view model starts out idle and not busy</summary>
+    [Test]
+    public void NewInstanceIsNotBusy() {
+      using(var viewModel = new TestViewModel(new DummyContext())) {
+        Assert.IsFalse(viewModel.IsBusy);
+      }
+    }
+
+    /// <summary>
+    ///   Verifies that errors happening in the background processing threads are
+    ///   reported to the main thread
+    /// </summary>
+    [Test]
+    public void ErrorsInBackgroundThreadAreReported() {
+      using(var viewModel = new TestViewModel(new DummyContext())) {
+        var testError = new ArgumentException("Mooh");
+        viewModel.CauseErrorInBackgroundThread(testError);
+        viewModel.WaitUntilFinished();
+        Assert.AreSame(testError, viewModel.ReportedError);
+      }
+    }
+
+  }
+
+} // namespace Nuclex.Windows.Forms.ViewModels
+
+#endif // UNITTEST
\ No newline at end of file
diff --git a/Source/ViewModels/ThreadedViewModel.cs b/Source/ViewModels/ThreadedViewModel.cs
new file mode 100644
index 0000000..b321ded
--- /dev/null
+++ b/Source/ViewModels/ThreadedViewModel.cs
@@ -0,0 +1,243 @@
+#region CPL License
+/*
+Nuclex Framework
+Copyright (C) 2002-2019 Nuclex Development Labs
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the IBM Common Public License as
+published by the IBM Corporation; either version 1.0 of the
+License, or (at your option) any later version.
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+IBM Common Public License for more details.
+
+You should have received a copy of the IBM Common Public
+License along with this library
+*/
+#endregion
+
+using System;
+using System.ComponentModel;
+using System.Windows.Forms;
+
+using Nuclex.Support;
+using Nuclex.Support.Threading;
+
+namespace Nuclex.Windows.Forms.ViewModels {
+
+  /// <summary>View model that can execute tasks in a background thread</summary>
+  public abstract class ThreadedViewModel : Observable, IDisposable {
+
+    #region class ViewModelThreadRunner
+
+    /// <summary>Thread runner for the threaded view model</summary>
+    private class ViewModelThreadRunner : ThreadRunner {
+
+      /// <summary>Initializes a new thread runner for the threaded view model</summary>
+      public ViewModelThreadRunner(ThreadedViewModel viewModel) {
+        this.viewModel = viewModel;
+      }
+
+      /// <summary>Reports an error</summary>
+      /// <param name="exception">Error that will be reported</param>
+      protected override void ReportError(Exception exception) {
+        this.viewModel.reportErrorFromThread(exception);
+      }
+
+      /// <summary>Called when the status of the busy flag changes</summary>
+      protected override void BusyChanged() {
+        this.viewModel.OnIsBusyChanged();
+      }
+
+      /// <summary>View model the thread runner belongs to</summary>
+      private ThreadedViewModel viewModel;
+
+    }
+
+    #endregion // class ViewModelThreadRunner
+
+    /// <summary>Initializes a new view model for background processing</summary>
+    /// <param name="uiContext">
+    ///   UI dispatcher that can be used to run callbacks in the UI thread
+    /// </param>
+    protected ThreadedViewModel(ISynchronizeInvoke uiContext = null) {
+      if(uiContext == null) {
+        this.uiContext = getMainWindow();
+      } else {
+        this.uiContext = uiContext;
+      }
+
+      this.reportErrorDelegate = new Action<Exception>(ReportError);
+
+      this.threadRunner = new ViewModelThreadRunner(this);
+    }
+
+    /// <summary>Immediately releases all resources owned by the instance</summary>
+    public virtual void Dispose() {
+      if(this.threadRunner != null) {
+        this.threadRunner.Dispose();
+        this.threadRunner = null;
+      }
+    }
+
+    /// <summary>Whether the view model is currently busy executing a task</summary>
+    public bool IsBusy {
+      get { return this.threadRunner.IsBusy; }
+    }
+
+    /// <summary>Reports an error to the user</summary>
+    /// <param name="exception">Error that will be reported</param>
+    /// <remarks>
+    ///   <para>
+    ///     You can use this method as a default handling method for your own error reporting
+    ///     (displaying the error to the user, logging it or whatever else is appropriate).
+    ///   </para>
+    ///   <para>
+    ///     When <see cref="RunInBackground(System.Action)" /> is used, this method will also
+    ///     be called in case an exception within the asynchronously running code goes unhandled.
+    ///     This choice was made because, in the context of UI code, you would wrap any
+    ///     operations that might fail in a try..catch pair anyway in order to inform
+    ///     the user instead of aborting the entire application.
+    ///   </para>
+    /// </remarks>
+    protected abstract void ReportError(Exception exception);
+
+    /// <summary>Executes the specified operation in the background</summary>
+    /// <param name="action">Action that will be executed in the background</param>
+    protected void RunInBackground(Action action) {
+      this.threadRunner.RunInBackground(action);
+    }
+
+    /// <summary>Executes the specified operation in the background</summary>
+    /// <param name="action">Action that will be executed in the background</param>
+    protected void RunInBackground(CancellableAction action) {
+      this.threadRunner.RunInBackground(action);
+    }
+
+    /// <summary>Executes the specified operation in the background</summary>
+    /// <param name="action">Action that will be executed in the background</param>
+    /// <param name="parameter1">Parameter that will be passed to the action</param>
+    protected void RunInBackground<P1>(Action<P1> action, P1 parameter1) {
+      this.threadRunner.RunInBackground(action, parameter1);
+    }
+
+    /// <summary>Executes the specified operation in the background</summary>
+    /// <param name="action">Action that will be executed in the background</param>
+    /// <param name="parameter1">Parameter that will be passed to the action</param>
+    protected void RunInBackground<P1>(CancellableAction<P1> action, P1 parameter1) {
+      this.threadRunner.RunInBackground(action, parameter1);
+    }
+
+    /// <summary>Executes the specified operation in the background</summary>
+    /// <param name="action">Action that will be executed in the background</param>
+    /// <param name="parameter1">First parameter that will be passed to the action</param>
+    /// <param name="parameter2">Second parameter that will be passed to the action</param>
+    protected void RunInBackground<P1, P2>(Action<P1, P2> action, P1 parameter1, P2 parameter2) {
+      this.threadRunner.RunInBackground(action, parameter1, parameter2);
+    }
+
+    /// <summary>Executes the specified operation in the background</summary>
+    /// <param name="action">Action that will be executed in the background</param>
+    /// <param name="parameter1">First parameter that will be passed to the action</param>
+    /// <param name="parameter2">Second parameter that will be passed to the action</param>
+    protected void RunInBackground<P1, P2>(
+      CancellableAction<P1, P2> action, P1 parameter1, P2 parameter2
+    ) {
+      this.threadRunner.RunInBackground(action, parameter1, parameter2);
+    }
+
+    /// <summary>Cancels the currently running background operation</summary>
+    protected void CancelBackgroundOperation() {
+      this.threadRunner.CancelBackgroundOperation();
+    }
+
+    /// <summary>Cancels all queued and the currently running background operation</summary>
+    protected void CancelAllBackgroundOperations() {
+      this.threadRunner.CancelAllBackgroundOperations();
+    }
+
+    /// <summary>Whether the background operation has been cancelled</summary>
+    //[Obsolete("Please use a method accepting a cancellation token instead of using this")]
+    protected bool IsBackgroundOperationCancelled {
+      get { return this.threadRunner.IsBackgroundOperationCancelled; }
+    }
+
+    /// <summary>Throws an exception if the background operation was cancelled</summary>
+    //[Obsolete("Please use a method accepting a cancellation token instead of using this")]
+    protected void ThrowIfBackgroundOperationCancelled() {
+      this.threadRunner.ThrowIfBackgroundOperationCancelled();
+    }
+
+    /// <summary>Executes the specified action in the UI thread</summary>
+    /// <param name="action">Action that will be executed in the UI thread</param>
+    protected void RunInUIThread(Action action) {
+      this.uiContext.Invoke(action, EmptyObjectArray);
+    }
+
+    /// <summary>Executes the specified action in the UI thread</summary>
+    /// <param name="action">Action that will be executed in the UI thread</param>
+    /// <param name="parameter1">Parameter that will be passed to the action</param>
+    protected void RunInUIThread<P1>(Action<P1> action, P1 parameter1) {
+      this.uiContext.Invoke(action, new object[1] { parameter1 });
+    }
+
+    /// <summary>Executes the specified action in the UI thread</summary>
+    /// <param name="action">Action that will be executed in the UI thread</param>
+    /// <param name="parameter1">First parameter that will be passed to the action</param>
+    /// <param name="parameter2">Second parameter that will be passed to the action</param>
+    protected void RunInUIThread<P1, P2>(Action<P1, P2> action, P1 parameter1, P2 parameter2) {
+      this.uiContext.Invoke(action, new object[2] { parameter1, parameter2 });
+    }
+
+    /// <summary>Called when the thread runner's busy flag changes</summary>
+    protected virtual void OnIsBusyChanged() {
+      OnPropertyChanged(nameof(IsBusy));
+    }
+
+    /// <summary>Reports an error that occurred in the runner's background thread</summary>
+    /// <param name="exception">Exception that the thread has encountered</param>
+    private void reportErrorFromThread(Exception exception) {
+      this.uiContext.Invoke(this.reportErrorDelegate, new object[1] { exception });
+    }
+
+    /// <summary>Finds the application's main window</summary>
+    /// <returns>Main window of the application</returns>
+    private static Form getMainWindow() {
+      IntPtr mainWindowHandle = System.Diagnostics.Process.GetCurrentProcess().MainWindowHandle;
+
+      // We can get two things: a list of all open windows and the handle of
+      // the window that the process has registered as main window. Use the latter
+      // to pick the correct window from the former.
+      FormCollection openForms = Application.OpenForms;
+      int openFormCount = openForms.Count;
+      for(int index = 0; index < openFormCount; ++index) {
+        if(openForms[index].IsHandleCreated) {
+          if(openForms[index].Handle == mainWindowHandle) {
+            return openForms[index];
+          }
+        }
+      }
+
+      // No matching main window found: use the first one in good faith or fail.
+      if(openFormCount > 0) {
+        return openForms[0];
+      } else {
+        return null;
+      }
+    }
+
+    /// <summary>An array of zero objects</summary>
+    private static readonly object[] EmptyObjectArray = new object[0];
+
+    /// <summary>UI dispatcher of the thread in which the view runs</summary>
+    private ISynchronizeInvoke uiContext;
+    /// <summary>Delegate for the ReportError() method</summary>
+    private Action<Exception> reportErrorDelegate;
+    /// <summary>Thread runner that manages the view model's thread</summary>
+    private ViewModelThreadRunner threadRunner;
+
+  }
+
+} // namespace Nuclex.Windows.Forms.ViewModels
diff --git a/Source/Views/IView.cs b/Source/Views/IView.cs
new file mode 100644
index 0000000..67221f1
--- /dev/null
+++ b/Source/Views/IView.cs
@@ -0,0 +1,37 @@
+#region CPL License
+/*
+Nuclex Framework
+Copyright (C) 2002-2019 Nuclex Development Labs
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the IBM Common Public License as
+published by the IBM Corporation; either version 1.0 of the
+License, or (at your option) any later version.
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+IBM Common Public License for more details.
+
+You should have received a copy of the IBM Common Public
+License along with this library
+*/
+#endregion
+
+using System;
+
+namespace Nuclex.Windows.Forms.Views {
+
+  /// <summary>View with support for data binding</summary>
+  public interface IView {
+
+    /// <summary>Provides the data binding target for the view</summary>
+    /// <remarks>
+    ///   This property is identical to the same-named one in WPF, it provides
+    ///   the view model to which the view should bind its controls.
+    /// </remarks>
+    object DataContext { get; set; }
+
+  }
+
+} // namespace Nuclex.Windows.Forms.Views
diff --git a/Source/Views/ViewControl.cs b/Source/Views/ViewControl.cs
new file mode 100644
index 0000000..e8ea3b9
--- /dev/null
+++ b/Source/Views/ViewControl.cs
@@ -0,0 +1,87 @@
+#region CPL License
+/*
+Nuclex Framework
+Copyright (C) 2002-2019 Nuclex Development Labs
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the IBM Common Public License as
+published by the IBM Corporation; either version 1.0 of the
+License, or (at your option) any later version.
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+IBM Common Public License for more details.
+
+You should have received a copy of the IBM Common Public
+License along with this library
+*/
+#endregion
+
+using System;
+using System.ComponentModel;
+using System.Windows.Forms;
+
+using Nuclex.Support;
+
+namespace Nuclex.Windows.Forms.Views {
+
+  /// <summary>
+  ///   Base class for MVVM user controls that act as views connected to a view model
+  /// </summary>
+  public class ViewControl : UserControl, IView {
+
+    /// <summary>Initializes a new view control</summary>
+    public ViewControl() {
+      this.onViewModelPropertyChangedDelegate = OnViewModelPropertyChanged;
+    }
+
+		/// <summary>Called when the control's data context is changed</summary>
+		/// <param name="sender">Control whose data context was changed</param>
+		/// <param name="oldDataContext">Data context that was previously used</param>
+		/// <param name="newDataContext">Data context that will be used from now on</param>
+		protected virtual void OnDataContextChanged(
+      object sender, object oldDataContext, object newDataContext
+    ) {
+      var oldViewModel = oldDataContext as INotifyPropertyChanged;
+      if(oldViewModel != null) {
+        oldViewModel.PropertyChanged -= this.onViewModelPropertyChangedDelegate;
+      }
+
+      var newViewModel = newDataContext as INotifyPropertyChanged;
+      if(newViewModel != null) {
+        newViewModel.PropertyChanged += this.onViewModelPropertyChangedDelegate;
+        InvalidateAllViewModelProperties();
+      }
+    }
+
+    /// <summary>Refreshes all properties from the view model</summary>
+    protected void InvalidateAllViewModelProperties() {
+      OnViewModelPropertyChanged(this.dataContext, PropertyChangedEventArgsHelper.Wildcard);
+    }
+
+    /// <summary>Called when a property of the view model is changed</summary>
+    /// <param name="sender">View model in which a property was changed</param>
+    /// <param name="arguments">Contains the name of the property that has changed</param>
+    protected virtual void OnViewModelPropertyChanged(
+      object sender, PropertyChangedEventArgs arguments
+    ) { }
+
+    /// <summary>Provides the data binding target for the view</summary>
+    public object DataContext {
+      get { return this.dataContext; }
+      set {
+        if(value != this.dataContext) {
+          this.dataContext = value;
+        }
+      }
+    }
+
+    /// <summary>Active data binding target, can be null</summary>
+    private object dataContext;
+    /// <summary>Delegate for the OnViewModelPropertyChanged() method</summary>
+    private PropertyChangedEventHandler onViewModelPropertyChangedDelegate;
+
+  }
+
+} // namespace Nuclex.Windows.Forms.Views
diff --git a/Source/Views/ViewForm.cs b/Source/Views/ViewForm.cs
new file mode 100644
index 0000000..f9aa329
--- /dev/null
+++ b/Source/Views/ViewForm.cs
@@ -0,0 +1,87 @@
+#region CPL License
+/*
+Nuclex Framework
+Copyright (C) 2002-2019 Nuclex Development Labs
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the IBM Common Public License as
+published by the IBM Corporation; either version 1.0 of the
+License, or (at your option) any later version.
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+IBM Common Public License for more details.
+
+You should have received a copy of the IBM Common Public
+License along with this library
+*/
+#endregion
+
+using System;
+using System.ComponentModel;
+using System.Windows.Forms;
+
+using Nuclex.Support;
+
+namespace Nuclex.Windows.Forms.Views {
+
+  /// <summary>
+  ///   Base class for MVVM windows that act as views connected to a view model
+  /// </summary>
+  public class ViewForm : Form, IView {
+
+    /// <summary>Initializes a new view control</summary>
+    public ViewForm() {
+      this.onViewModelPropertyChangedDelegate = OnViewModelPropertyChanged;
+    }
+
+		/// <summary>Called when the window's data context is changed</summary>
+		/// <param name="sender">Window whose data context was changed</param>
+		/// <param name="oldDataContext">Data context that was previously used</param>
+		/// <param name="newDataContext">Data context that will be used from now on</param>
+		protected virtual void OnDataContextChanged(
+      object sender, object oldDataContext, object newDataContext
+    ) {
+      var oldViewModel = oldDataContext as INotifyPropertyChanged;
+      if(oldViewModel != null) {
+        oldViewModel.PropertyChanged -= this.onViewModelPropertyChangedDelegate;
+      }
+
+      var newViewModel = newDataContext as INotifyPropertyChanged;
+      if(newViewModel != null) {
+        newViewModel.PropertyChanged += this.onViewModelPropertyChangedDelegate;
+        InvalidateAllViewModelProperties();
+      }
+    }
+
+    /// <summary>Refreshes all properties from the view model</summary>
+    protected void InvalidateAllViewModelProperties() {
+      OnViewModelPropertyChanged(this.dataContext, PropertyChangedEventArgsHelper.Wildcard);
+    }
+
+    /// <summary>Called when a property of the view model is changed</summary>
+    /// <param name="sender">View model in which a property was changed</param>
+    /// <param name="arguments">Contains the name of the property that has changed</param>
+    protected virtual void OnViewModelPropertyChanged(
+      object sender, PropertyChangedEventArgs arguments
+    ) { }
+
+    /// <summary>Provides the data binding target for the view</summary>
+    public object DataContext {
+      get { return this.dataContext; }
+      set {
+        if(value != this.dataContext) {
+          this.dataContext = value;
+        }
+      }
+    }
+
+    /// <summary>Active data binding target, can be null</summary>
+    private object dataContext;
+    /// <summary>Delegate for the OnViewModelPropertyChanged() method</summary>
+    private PropertyChangedEventHandler onViewModelPropertyChangedDelegate;
+
+  }
+
+} // namespace Nuclex.Windows.Forms.Views