dialog sessions, and opening event. thoroughly untested right now :)

Author: ButchersBoy

MainDemo.Wpf/Domain/DialogsViewModel.cs

@@ -20,7 +20,7 @@ private async void ExecuteRunDialog(object o)
             {
                 DataContext = new object()
             };
-
+            
             //show the dialog
             var result = await DialogHost.Show(view, "RootDialog", ClosingEventHandler);
 

MaterialDesignThemes.Wpf/DialogClosingEventArgs.cs

@@ -1,42 +1,61 @@
-using System.Windows;
+using System;
+using System.Windows;
 
 namespace MaterialDesignThemes.Wpf
 {
     public class DialogClosingEventArgs : RoutedEventArgs
     {
-        public DialogClosingEventArgs(object parameter, object content)
+        public DialogClosingEventArgs(DialogSession session, object parameter)
         {
-            Parameter = parameter;
-            Content = content;
+            if (session == null) throw new ArgumentNullException(nameof(session));
+            Session = session;
+
+            Parameter = parameter;         
         }
 
-        public DialogClosingEventArgs(object parameter, object content, RoutedEvent routedEvent) : base(routedEvent)
+        public DialogClosingEventArgs(DialogSession session, object parameter, RoutedEvent routedEvent) : base(routedEvent)
         {
-            Parameter = parameter;
-            Content = content;
+            if (session == null) throw new ArgumentNullException(nameof(session));
+            Session = session;
+
+            Parameter = parameter;            
         }
 
-        public DialogClosingEventArgs(object parameter, object content, RoutedEvent routedEvent, object source) : base(routedEvent, source)
+        public DialogClosingEventArgs(DialogSession session, object parameter, RoutedEvent routedEvent, object source) : base(routedEvent, source)
         {
-            Parameter = parameter;
-            Content = content;
+            if (session == null) throw new ArgumentNullException(nameof(session));
+            Session = session;
+
+            Parameter = parameter;            
         }
 
+        /// <summary>
+        /// Cancel the close.
+        /// </summary>
         public void Cancel()
         {
             IsCancelled = true;
         }
 
+        /// <summary>
+        /// Indicates if the close has already been cancelled.
+        /// </summary>
         public bool IsCancelled { get; private set; }
 
         /// <summary>
         /// Gets the paramter originally provided to <see cref="DialogHost.CloseDialogCommand"/>/
         /// </summary>
         public object Parameter { get; }
 
+        /// <summary>
+        /// Allows interation with the current dialog session.
+        /// </summary>
+        public DialogSession Session { get; }
+
         /// <summary>
         /// Gets the <see cref="DialogHost.DialogContent"/> which is currently displayed, so this could be a view model or a UI element.
         /// </summary>
-        public object Content { get; }
+        [Obsolete("Prefer Session.Content")]
+        public object Content => Session.Content;
     }
 }

MaterialDesignThemes.Wpf/DialogHost.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Windows;
+
+namespace MaterialDesignThemes.Wpf
+{
+    public class DialogOpenedEventArgs : RoutedEventArgs
+    {
+        public DialogOpenedEventArgs(DialogSession session, RoutedEvent routedEvent)
+        {
+            if (session == null) throw new ArgumentNullException(nameof(session));
+
+            Session = session;
+            RoutedEvent = routedEvent;
+        }
+
+        /// <summary>
+        /// Allows interation with the current dialog session.
+        /// </summary>
+        public DialogSession Session { get; }
+    }
+}

MaterialDesignThemes.Wpf/DialogOpenedEventArgs.cs

@@ -0,0 +1,4 @@
+namespace MaterialDesignThemes.Wpf
+{
+    public delegate void DialogOpenedEventHandler(object sender, DialogOpenedEventArgs eventArgs);
+}

MaterialDesignThemes.Wpf/DialogOpenedEventHandler.cs

@@ -0,0 +1,69 @@
+using System;
+
+namespace MaterialDesignThemes.Wpf
+{
+    /// <summary>
+    /// Allows an open dialog to be managed. Use is only permitted during a single display operation.
+    /// </summary>
+    public class DialogSession
+    {
+        private readonly DialogHost _owner;
+        internal bool IsDisabled;
+
+        internal DialogSession(DialogHost owner)
+        {
+            if (owner == null) throw new ArgumentNullException(nameof(owner));
+
+            _owner = owner;
+        }
+
+        /// <summary>
+        /// Gets the <see cref="DialogHost.DialogContent"/> which is currently displayed, so this could be a view model or a UI element.
+        /// </summary>
+        /// <exception cref="InvalidOperationException">Thrown if the dialog session has ended.</exception>
+        public object Content
+        {
+            get
+            {
+                if (IsDisabled) throw new InvalidOperationException("Dialog session has ended.");
+
+                return _owner.DialogContent;
+            }
+        }
+
+        /// <summary>
+        /// Update the currrent content in the dialog.
+        /// </summary>
+        /// <param name="content"></param>
+        /// <exception cref="InvalidOperationException">Thrown if the dialog content is currently set via a binding, or if the dialog session has ended.</exception>
+        public void UpdateContent(object content)
+        {
+            if (content == null) throw new ArgumentNullException(nameof(content));
+            if (IsDisabled) throw new InvalidOperationException("Dialog session has ended.");
+
+            _owner.AssertTargetableContent();
+            _owner.DialogContent = content;
+        }
+
+        /// <summary>
+        /// Closes the dialog.
+        /// </summary>
+        /// <exception cref="InvalidOperationException">Thrown if the dialog session has ended, or a close operation is currently in progress.</exception>
+        public void Close()
+        {
+            if (IsDisabled) throw new InvalidOperationException("Dialog session has ended.");
+
+        }
+
+        /// <summary>
+        /// Closes the dialog.
+        /// </summary>
+        /// <param name="parameter">Result parameter which will be returned in <see cref="DialogClosingEventArgs.Parameter"/> or from <see cref="DialogHost.Show(object)"/> method.</param>
+        /// <exception cref="InvalidOperationException">Thrown if the dialog session has ended, or a close operation is currently in progress.</exception>
+        public void Close(object parameter)
+        {
+            if (IsDisabled) throw new InvalidOperationException("Dialog session has ended.");
+
+        }
+    }
+}

MaterialDesignThemes.Wpf/DialogSession.cs

@@ -229,6 +229,9 @@
     <Compile Include="DateTimeEx.cs" />
     <Compile Include="DialogClosingEventArgs.cs" />
     <Compile Include="DialogClosingEventHandler.cs" />
+    <Compile Include="DialogOpenedEventArgs.cs" />
+    <Compile Include="DialogOpenedEventHandler.cs" />
+    <Compile Include="DialogSession.cs" />
     <Compile Include="DialogHost.cs" />
     <Compile Include="DrawerHost.cs" />
     <Compile Include="ListSortDirectionIndicator.cs" />