Stylet/Stylet/WindowManager.cs

using Stylet.Logging;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows;
using System.Windows.Data;

namespace Stylet
{
    /// <summary>
    /// Manager capable of taking a ViewModel instance, instantiating its View and showing it as a dialog or window
    /// </summary>
    public interface IWindowManager
    {
        /// <summary>
        /// Given a ViewModel, show its corresponding View as a window
        /// </summary>
        /// <param name="viewModel">ViewModel to show the View for</param>
        void ShowWindow(object viewModel);

        /// <summary>
        /// Given a ViewModel, show its corresponding View as a Dialog
        /// </summary>
        /// <param name="viewModel">ViewModel to show the View for</param>
        /// <returns>DialogResult of the View</returns>
        bool? ShowDialog(object viewModel);

        /// <summary>
        /// Display a MessageBox
        /// </summary>
        /// <param name="messageBoxText">A <see cref="System.String"/> that specifies the text to display.</param>
        /// <param name="caption">A <see cref="System.String"/> that specifies the title bar caption to display.</param>
        /// <param name="buttons">A <see cref="System.Windows.MessageBoxButton"/> value that specifies which button or buttons to display.</param>
        /// <param name="icon">A <see cref="System.Windows.MessageBoxImage"/> value that specifies the icon to display.</param>
        /// <param name="defaultResult">A <see cref="System.Windows.MessageBoxResult"/> value that specifies the default result of the message box.</param>
        /// <param name="cancelResult">A <see cref="System.Windows.MessageBoxResult"/> value that specifies the cancel result of the message box</param>
        /// <param name="buttonLabels">A dictionary specifying the button labels, if desirable</param>
        /// <param name="flowDirection">The <see cref="System.Windows.FlowDirection"/> to use, overrides the <see cref="MessageBoxViewModel.DefaultFlowDirection"/></param>
        /// <param name="textAlignment">The <see cref="System.Windows.TextAlignment"/> to use, overrides the <see cref="MessageBoxViewModel.DefaultTextAlignment"/></param>
        /// <returns>The result chosen by the user</returns>
        MessageBoxResult ShowMessageBox(string messageBoxText, string caption = "",
            MessageBoxButton buttons = MessageBoxButton.OK,
            MessageBoxImage icon = MessageBoxImage.None,
            MessageBoxResult defaultResult = MessageBoxResult.None,
            MessageBoxResult cancelResult = MessageBoxResult.None,
            IDictionary<MessageBoxResult, string> buttonLabels = null,
            FlowDirection? flowDirection = null,
            TextAlignment? textAlignment = null);
    }

    /// <summary>
    /// Configuration passed to WindowManager (normally implemented by BootstrapperBase)
    /// </summary>
    public interface IWindowManagerConfig
    {
        /// <summary>
        /// Returns the currently-displayed window, or null if there is none (or it can't be determined)
        /// </summary>
        /// <returns>The currently-displayed window, or null</returns>
        Window GetActiveWindow();
    }

    /// <summary>
    /// Default implementation of IWindowManager, is capable of showing a ViewModel's View as a dialog or a window
    /// </summary>
    public class WindowManager : IWindowManager
    {
        private static readonly ILogger logger = LogManager.GetLogger(typeof(WindowManager));
        private readonly IViewManager viewManager;
        private readonly Func<IMessageBoxViewModel> messageBoxViewModelFactory;
        private readonly Func<Window> getActiveWindow;

        /// <summary>
        /// Initialises a new instance of the <see cref="WindowManager"/> class, using the given <see cref="IViewManager"/>
        /// </summary>
        /// <param name="viewManager">IViewManager to use when creating views</param>
        /// <param name="messageBoxViewModelFactory">Delegate which returns a new IMessageBoxViewModel instance when invoked</param>
        /// <param name="config">Configuration object</param>
        public WindowManager(IViewManager viewManager, Func<IMessageBoxViewModel> messageBoxViewModelFactory, IWindowManagerConfig config)
        {
            this.viewManager = viewManager;
            this.messageBoxViewModelFactory = messageBoxViewModelFactory;
            this.getActiveWindow = config.GetActiveWindow;
        }

        /// <summary>
        /// Given a ViewModel, show its corresponding View as a window
        /// </summary>
        /// <param name="viewModel">ViewModel to show the View for</param>
        public void ShowWindow(object viewModel)
        {
            this.ShowWindow(viewModel, null);
        }

        /// <summary>
        /// Given a ViewModel, show its corresponding View as a window, and set its owner
        /// </summary>
        /// <param name="viewModel">ViewModel to show the View for</param>
        /// <param name="ownerViewModel">The ViewModel for the View which should own this window</param>
        public void ShowWindow(object viewModel, IViewAware ownerViewModel)
        {
            this.CreateWindow(viewModel, false, ownerViewModel).Show();
        }

        /// <summary>
        /// Given a ViewModel, show its corresponding View as a Dialog
        /// </summary>
        /// <param name="viewModel">ViewModel to show the View for</param>
        /// <returns>DialogResult of the View</returns>
        public bool? ShowDialog(object viewModel)
        {
            return this.ShowDialog(viewModel, null);
        }

        /// <summary>
        /// Given a ViewModel, show its corresponding View as a Dialog, and set its owner
        /// </summary>
        /// <param name="viewModel">ViewModel to show the View for</param>
        /// <param name="ownerViewModel">The ViewModel for the View which should own this dialog</param>
        /// <returns>DialogResult of the View</returns>
        public bool? ShowDialog(object viewModel, IViewAware ownerViewModel)
        {
            return this.CreateWindow(viewModel, true, ownerViewModel).ShowDialog();
        }

        /// <summary>
        /// Display a MessageBox
        /// </summary>
        /// <param name="messageBoxText">A <see cref="System.String"/> that specifies the text to display.</param>
        /// <param name="caption">A <see cref="System.String"/> that specifies the title bar caption to display.</param>
        /// <param name="buttons">A <see cref="System.Windows.MessageBoxButton"/> value that specifies which button or buttons to display.</param>
        /// <param name="icon">A <see cref="System.Windows.MessageBoxImage"/> value that specifies the icon to display.</param>
        /// <param name="defaultResult">A <see cref="System.Windows.MessageBoxResult"/> value that specifies the default result of the message box.</param>
        /// <param name="cancelResult">A <see cref="System.Windows.MessageBoxResult"/> value that specifies the cancel result of the message box</param>
        /// <param name="buttonLabels">A dictionary specifying the button labels, if desirable</param>
        /// <param name="flowDirection">The <see cref="System.Windows.FlowDirection"/> to use, overrides the <see cref="MessageBoxViewModel.DefaultFlowDirection"/></param>
        /// <param name="textAlignment">The <see cref="System.Windows.TextAlignment"/> to use, overrides the <see cref="MessageBoxViewModel.DefaultTextAlignment"/></param>
        /// <returns>The result chosen by the user</returns>
        public MessageBoxResult ShowMessageBox(string messageBoxText, string caption = "",
            MessageBoxButton buttons = MessageBoxButton.OK,
            MessageBoxImage icon = MessageBoxImage.None,
            MessageBoxResult defaultResult = MessageBoxResult.None,
            MessageBoxResult cancelResult = MessageBoxResult.None,
            IDictionary<MessageBoxResult, string> buttonLabels = null,
            FlowDirection? flowDirection = null,
            TextAlignment? textAlignment = null)
        {
            var vm = this.messageBoxViewModelFactory();
            vm.Setup(messageBoxText, caption, buttons, icon, defaultResult, cancelResult, buttonLabels, flowDirection, textAlignment);
            this.ShowDialog(vm);
            return vm.ClickedButton;
        }

        /// <summary>
        /// Given a ViewModel, create its View, ensure that it's a Window, and set it up
        /// </summary>
        /// <param name="viewModel">ViewModel to create the window for</param>
        /// <param name="isDialog">True if the window will be used as a dialog</param>
        /// <param name="ownerViewModel">Optionally the ViewModel which owns the view which should own this window</param>
        /// <returns>Window which was created and set up</returns>
        protected virtual Window CreateWindow(object viewModel, bool isDialog, IViewAware ownerViewModel)
        {
            var view = this.viewManager.CreateAndBindViewForModelIfNecessary(viewModel);
            var window = view as Window;
            if (window == null)
            {
                var e = new StyletInvalidViewTypeException(String.Format("WindowManager.ShowWindow or .ShowDialog tried to show a View of type '{0}', but that View doesn't derive from the Window class. " +
                    "Make sure any Views you display using WindowManager.ShowWindow or .ShowDialog derive from Window (not UserControl, etc)",
                    view == null ? "(null)" : view.GetType().Name));
                logger.Error(e);
                throw e;
            }

            // Only set this it hasn't been set / bound to anything
            var haveDisplayName = viewModel as IHaveDisplayName;
            if (haveDisplayName != null && (String.IsNullOrEmpty(window.Title) || window.Title == view.GetType().Name) && BindingOperations.GetBindingBase(window, Window.TitleProperty) == null)
            {
                var binding = new Binding("DisplayName") { Mode = BindingMode.TwoWay };
                window.SetBinding(Window.TitleProperty, binding);
            }

            if (ownerViewModel?.View is Window explicitOwner)
            {
                window.Owner = explicitOwner;
            }
            else if (isDialog)
            {
                var owner = this.InferOwnerOf(window);
                if (owner != null)
                {
                    // We can end up in a really weird situation if they try and display more than one dialog as the application's closing
                    // Basically the MainWindow's no long active, so the second dialog chooses the first dialog as its owner... But the first dialog
                    // hasn't yet been shown, so we get an exception ("cannot set owner property to a Window which has not been previously shown").
                    try
                    {
                        window.Owner = owner;
                    }
                    catch (InvalidOperationException e)
                    {
                        logger.Error(e, "This can occur when the application is closing down");
                    }
                }
            }

            if (isDialog)
            {
                logger.Info("Displaying ViewModel {0} with View {1} as a Dialog", viewModel, window);
            }
            else
            {
                logger.Info("Displaying ViewModel {0} with View {1} as a Window", viewModel, window);
            }

            // If and only if they haven't tried to position the window themselves...
            // Has to be done after we're attempted to set the owner
            if (window.WindowStartupLocation == WindowStartupLocation.Manual && Double.IsNaN(window.Top) && Double.IsNaN(window.Left) &&
                BindingOperations.GetBinding(window, Window.TopProperty) == null && BindingOperations.GetBinding(window, Window.LeftProperty) == null)
            {
                window.WindowStartupLocation = window.Owner == null ? WindowStartupLocation.CenterScreen : WindowStartupLocation.CenterOwner;
            }

            // This gets itself retained by the window, by registering events
            // ReSharper disable once ObjectCreationAsStatement
            new WindowConductor(window, viewModel);

            return window;
        }

        private Window InferOwnerOf(Window window)
        {
            var active = this.getActiveWindow();
            return ReferenceEquals(active, window) ? null : active;
        }

        private class WindowConductor : IChildDelegate
        {
            private readonly Window window;
            private readonly object viewModel;

            public WindowConductor(Window window, object viewModel)
            {
                this.window = window;
                this.viewModel = viewModel;

                // They won't be able to request a close unless they implement IChild anyway...
                var viewModelAsChild = this.viewModel as IChild;
                if (viewModelAsChild != null)
                    viewModelAsChild.Parent = this;

                ScreenExtensions.TryActivate(this.viewModel);

                var viewModelAsScreenState = this.viewModel as IScreenState;
                if (viewModelAsScreenState != null)
                {
                    window.StateChanged += this.WindowStateChanged;
                    window.Closed += this.WindowClosed;
                }

                if (this.viewModel is IGuardClose)
                    window.Closing += this.WindowClosing;
            }

            private void WindowStateChanged(object sender, EventArgs e)
            {
                switch (this.window.WindowState)
                {
                    case WindowState.Maximized:
                    case WindowState.Normal:
                        logger.Info("Window {0} maximized/restored: activating", this.window);
                        ScreenExtensions.TryActivate(this.viewModel);
                        break;

                    case WindowState.Minimized:
                        logger.Info("Window {0} minimized: deactivating", this.window);
                        ScreenExtensions.TryDeactivate(this.viewModel);
                        break;
                }
            }

            private void WindowClosed(object sender, EventArgs e)
            {
                // Logging was done in the Closing handler

                this.window.StateChanged -= this.WindowStateChanged;
                this.window.Closed -= this.WindowClosed;
                this.window.Closing -= this.WindowClosing; // Not sure this is required

                ScreenExtensions.TryClose(this.viewModel);
            }

            private async void WindowClosing(object sender, CancelEventArgs e)
            {
                if (e.Cancel)
                    return;

                logger.Info("ViewModel {0} close requested because its View was closed", this.viewModel);

                // See if the task completed synchronously
                var task = ((IGuardClose)this.viewModel).CanCloseAsync();
                if (task.IsCompleted)
                {
                    // The closed event handler will take things from here if we don't cancel
                    if (!task.Result)
                        logger.Info("Close of ViewModel {0} cancelled because CanCloseAsync returned false", this.viewModel);
                    e.Cancel = !task.Result;
                }
                else
                {
                    e.Cancel = true;
                    logger.Info("Delaying closing of ViewModel {0} because CanCloseAsync is completing asynchronously", this.viewModel);
                    if (await task)
                    {
                        this.window.Closing -= this.WindowClosing;
                        this.window.Close();
                        // The Closed event handler handles unregistering the events, and closing the ViewModel
                    }
                    else
                    {
                        logger.Info("Close of ViewModel {0} cancelled because CanCloseAsync returned false", this.viewModel);
                    }
                }
            }

            /// <summary>
            /// Close was requested by the child
            /// </summary>
            /// <param name="item">Item to close</param>
            /// <param name="dialogResult">DialogResult to close with, if it's a dialog</param>
            async void IChildDelegate.CloseItem(object item, bool? dialogResult)
            {
                if (item != this.viewModel)
                {
                    logger.Warn("IChildDelegate.CloseItem called with item {0} which is _not_ our ViewModel {1}", item, this.viewModel);
                    return;
                }

                var guardClose = this.viewModel as IGuardClose;
                if (guardClose != null && !await guardClose.CanCloseAsync())
                {
                    logger.Info("Close of ViewModel {0} cancelled because CanCloseAsync returned false", this.viewModel);
                    return;
                }

                logger.Info("ViewModel {0} close requested with DialogResult {1} because it called RequestClose", this.viewModel, dialogResult);

                this.window.StateChanged -= this.WindowStateChanged;
                this.window.Closed -= this.WindowClosed;
                this.window.Closing -= this.WindowClosing;

                // Need to call this after unregistering the event handlers, as it causes the window
                // to be closed
                if (dialogResult != null)
                    this.window.DialogResult = dialogResult;

                ScreenExtensions.TryClose(this.viewModel);

                this.window.Close();
            }
        }
    }
}