Nuclex.Windows.Forms/Source/Views/MultiPageViewForm.cs

#region Apache License 2.0
/*
Nuclex .NET Framework
Copyright (C) 2002-2024 Markus Ewald / Nuclex Development Labs

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#endregion // Apache License 2.0

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Windows.Forms;

using Nuclex.Support;
using Nuclex.Windows.Forms.ViewModels;

namespace Nuclex.Windows.Forms.Views {

  /// <summary>Special view form that can display different child views</summary>
  public class MultiPageViewForm : ViewForm {

    #region struct RedrawLockScope

    /// <summary>Prevents controls from redrawing themselves for a while</summary>
    private struct RedrawLockScope : IDisposable {

      /// <summary>Window message that enables or disables control redraw</summary>
      private const int WM_SETREDRAW = 11;

      /// <summary>Sends a window message to the specified window</summary>
      /// <param name="windowHandle">Window a message will be sent to</param>
      /// <param name="messageId">ID of the message that will be sent</param>
      /// <param name="firstArgument">First argument to the window procedure</param>
      /// <param name="secondArgument">Second argument to the window procedure</param>
      /// <returns>The return value of the window procedure</returns>
      [DllImport("user32")]
      public static extern int SendMessage(
        IntPtr windowHandle, int messageId, bool firstArgument, int secondArgument
      );

      /// <summary>Stops redrawing the specified control</summary>
      /// <param name="control">Control to stop redrawing</param>
      public RedrawLockScope(Control control) {
        if(Environment.OSVersion.Platform == PlatformID.Win32NT) {
          SendMessage(control.Handle, WM_SETREDRAW, false, 0);
          this.control = control;
        } else {
          this.control = null;
        }
      }

      /// <summary>Enables redrawing again when the lock scope is disposed</summary>
      public void Dispose() {
        if(this.control != null) {
          SendMessage(this.control.Handle, WM_SETREDRAW, true, 0);
          this.control.Invalidate(true);
        }
      }

      /// <summary>Control that has been stopped from redrawing itself</summary>
      private Control control;

    }

    #endregion // struct RedrawLockScope

    /// <summary>Initializes a new multi page view window for the windows forms designer</summary>
    public MultiPageViewForm() {
      this.createViewMethod = typeof(IWindowManager).GetMethod(nameof(IWindowManager.CreateView));
    }

    /// <summary>Initializes a new multi page view window</summary>
    /// <param name="windowManager">
    ///   Window manager that is used to set up the child views
    /// </param>
    /// <param name="cachePageViews">Whether page views should be kept alive and reused</param>
    public MultiPageViewForm(IWindowManager windowManager, bool cachePageViews = false) {
      this.windowManager = windowManager;
      this.createViewMethod = typeof(IWindowManager).GetMethod(nameof(IWindowManager.CreateView));

      if(cachePageViews) {
        this.cachedViews = new Dictionary<Type, Control>();
      }
    }

    /// <summary>Called when the control is being disposed</summary>
    /// <param name="calledExplicitly">
    ///   Whether the call was made by user code (vs. the garbage collector)
    /// </param>
    protected override void Dispose(bool calledExplicitly) {
      if(calledExplicitly) {

        // Disable the active view, if any
        if(this.activePageView != null) {
          if(this.childViewContainer != null) {
            this.childViewContainer.Controls.Remove(this.activePageView);
          }
        }

        // If caching is disabled, dispose of the active child view, if any
        if(this.cachedViews == null) {
          if(this.activePageView != null) {
            disposeIfSupported(this.activePageView);
            this.activePageView = null;
          }
        } else { // Caching is enabled, dispose of any cached child views
          foreach(Control childView in this.cachedViews.Values) {
            disposeIfSupported(childView);
          }
          this.cachedViews.Clear();
          this.cachedViews = null;
          this.activePageView = null;
        }
      }

      base.Dispose(calledExplicitly);
    }

    /// <summary>Discovers the container control used to host the child views</summary>
    /// <returns>The container control is which the child views will be hosted</returns>
    /// <remarks>
    ///   This is supposed to be overriden by the user, simply returning the container
    ///   control that should host the page views. If it isn't, however, we use some
    ///   heuristics to figure out the most likely candidate: it should be a container,
    ///   and it should cover most of the window's client area.
    /// </remarks>
    protected virtual Control IdentifyPageContainer() {
      Size halfWindowSize = Size;
      halfWindowSize.Width /= 2;
      halfWindowSize.Height /= 2;

      // First container control we found -- if we find no likely candidate,
      // we simply use the first
      Control firstContainer = null;

      // Check all top-level controls in the window. If there's a container that
      // covers most of the window, it's our best bet
      int controlCount = Controls.Count;
      for(int index = 0; index < controlCount; ++index) {
        Control control = Controls[index];

        // Only check container controls
        if((control is ContainerControl) || (control is Panel)) {
          if(firstContainer == null) {
            firstContainer = control;
          }

          // If this control covers most of the view, it's our candidate!
          Size controlSize = control.Size;
          bool goodCandidate = (
            (controlSize.Width > halfWindowSize.Width) &&
            (controlSize.Height > halfWindowSize.Height)
          );
          if(goodCandidate) {
            return control;
          }
        }
      }

      // If no candidate was found, return the first container control we encountered
      // or create a new UserControl as the container if nothing was found at all.
      if(firstContainer == null) {
        firstContainer = new Panel();
        Controls.Add(firstContainer);
        firstContainer.Dock = DockStyle.Fill;
      }

      return firstContainer;
    }

    /// <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 override void OnDataContextChanged(
      object sender, object oldDataContext, object newDataContext
    ) {

      // Kill the currently active view if there was an old view model.
      if(oldDataContext != null) {
        disableActivePageView();
      }

      base.OnDataContextChanged(sender, oldDataContext, newDataContext);

      // If a valid view model was assigned, create a new view its active page view model
      if(newDataContext != null) {
        var dataContextAsMultiPageViewModel = newDataContext as IMultiPageViewModel;
        if(dataContextAsMultiPageViewModel != null) {
          activatePageView(dataContextAsMultiPageViewModel.GetActivePageViewModel());
        }
      }

    }

    /// <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 override void OnViewModelPropertyChanged(
      object sender, PropertyChangedEventArgs arguments
    ) {
      base.OnViewModelPropertyChanged(sender, arguments);

      if(arguments.AreAffecting(nameof(MultiPageViewModel<object>.ActivePage))) {
        var viewModelAsMultiPageviewModel = DataContext as IMultiPageViewModel;
        if(viewModelAsMultiPageviewModel != null) {
          if(InvokeRequired) {
            Invoke(
              new Action<object>(activatePageView),
              viewModelAsMultiPageviewModel.GetActivePageViewModel()
            );
          } else {
            activatePageView(viewModelAsMultiPageviewModel.GetActivePageViewModel());
          }
        }
      }
    }

    /// <summary>Currently active page view control</summary>
    protected Control ActivePageView {
      get { return this.activePageView; }
    }

    /// <summary>The view model running the currently active page</summary>
    protected object ActivePageViewModel {
      get {
        var activePageViewAsView = this.activePageView as IView;
        if(activePageViewAsView == null) {
          return null;
        } else {
          return activePageViewAsView.DataContext;
        }
      }
    }

    /// <summary>Activates the page view for the specified page view model</summary>
    /// <param name="pageViewModel">
    ///   Page view model for which the page view will be activated
    /// </param>
    private void activatePageView(object pageViewModel) {
      object activePageViewModel = null;
      {
        var activePageViewAsView = this.activePageView as IView;
        if(activePageViewAsView != null) {
          activePageViewModel = activePageViewAsView.DataContext;
        }
      }

      // Try from the cheapest to the most expensive way to get to our goal,
      // an activated view suiting the specified view model.

      // If we already have the target view model selected, do nothing
      if(activePageViewModel == pageViewModel) {
        return;
      }

      // If the page view model for the old and the new page are of the same
      // type, we can reuse the currently active page view
      if((activePageViewModel != null) && (pageViewModel != null)) {
        if(pageViewModel.GetType() == this.activePageView.GetType()) {
          var activePageViewAsView = this.activePageView as IView;
          if(activePageViewAsView != null) {
            activePageViewAsView.DataContext = pageViewModel;
          }

          return;
        }
      }

      // Worst, but usual, case: the new page view model might require
      // a different view. Create or look up the new view and put it in the container
      {
        if(pageViewModel == null) {
          disableActivePageView();
        } else {
          Control pageViewContainer = getPageViewContainer();
          using(new RedrawLockScope(pageViewContainer)) {
            disableActivePageView();

            this.activePageView = getOrCreatePageView(pageViewModel);
            pageViewContainer.Controls.Add(this.activePageView);
            this.activePageView.Dock = DockStyle.Fill;
          }
        }
      }
    }

    /// <summary>Gets the cached child view or creates a new one if not cached</summary>
    /// <param name="viewModel">View model for which a child view will be returned</param>
    /// <returns>A child view suitable for the specified view model</returns>
    private Control getOrCreatePageView(object viewModel) {
      Type viewModelType = viewModel.GetType();

      Control view;

      // If caching is enabled, check if we have a cached view
      if(this.cachedViews != null) {
        if(this.cachedViews.TryGetValue(viewModelType, out view)) {
          return view;
        }
      }

      // Otherwise, call the window manager's CreateView() method
      MethodInfo specializedCreateViewMethod = (
        this.createViewMethod.MakeGenericMethod(viewModelType)
      );
      view = (Control)specializedCreateViewMethod.Invoke(
        this.windowManager, new object[1] { viewModel }
      );

      // If caching is enabled, register the view in the cache
      if(this.cachedViews != null) {
        this.cachedViews.Add(viewModelType, view);
      }

      return view;
    }

    /// <summary>Disables the currently active page view control</summary>
    private void disableActivePageView() {
      if(this.activePageView != null) {
        Control container = getPageViewContainer();
        container.Controls.Remove(this.activePageView);

        // If we don't reuse views, kill it now
        if(this.cachedViews == null) {
          disposeIfSupported(this.activePageView);
          this.activePageView = null;
        } else {
          var activePageViewAsView = this.activePageView as IView;
          if(activePageViewAsView != null) {
            activePageViewAsView.DataContext = null;
          }
        }
      }
    }

    /// <summary>Fetches the container that holds the child views</summary>
    /// <returns>The container for the child views</returns>
    private Control getPageViewContainer() {
      if(this.childViewContainer == null) {
        this.childViewContainer = IdentifyPageContainer();
      }

      return this.childViewContainer;
    }

    /// <summary>Disposes the specified object if it is disposable</summary>
    /// <param name="potentiallyDisposable">Object that will be disposed if supported</param>
    private static void disposeIfSupported(object potentiallyDisposable) {
      var disposable = potentiallyDisposable as IDisposable;
      if(disposable != null) {
        disposable.Dispose();
      }
    }

    /// <summary>Window manager through which the child views are created</summary>
    private IWindowManager windowManager;
    /// <summary>Reflection info for the createView() method of the window manager</summary>
    private MethodInfo createViewMethod;

    /// <summary>Container in which the child views will be hosted</summary>
    private Control childViewContainer;
    /// <summary>Cached views that will be reused when the view model activates them</summary>
    private Dictionary<Type, Control> cachedViews;
    /// <summary>The currently active child view</summary>
    private Control activePageView;

  }

} // namespace Nuclex.Windows.Forms.Views