Added a Mdi Container feature.

Terminal.Gui/Core/Application.cs

@@ -10,7 +10,7 @@
 //   - "Colors" type or "Attributes" type?
 //   - What to surface as "BackgroundCOlor" when clearing a window, an attribute or colors?
 //
-// Optimziations
+// Optimizations
 //   - Add rendering limitation to the exposed area
 using System;
 using System.Collections;
@@ -23,7 +23,7 @@ using System.ComponentModel;
 namespace Terminal.Gui {
 
 	/// <summary>
-	/// A static, singelton class provding the main application driver for Terminal.Gui apps. 
+	/// A static, singleton class providing the main application driver for Terminal.Gui apps. 
 	/// </summary>
 	/// <example>
 	/// <code>
@@ -55,11 +55,36 @@ namespace Terminal.Gui {
 	///   </para>
 	/// </remarks>
 	public static class Application {
+		static Stack<Toplevel> toplevels = new Stack<Toplevel> ();
+
 		/// <summary>
 		/// The current <see cref="ConsoleDriver"/> in use.
 		/// </summary>
 		public static ConsoleDriver Driver;
 
+		/// <summary>
+		/// Gets all the Mdi childes which represent all the not modal <see cref="Toplevel"/> from the <see cref="MdiTop"/>.
+		/// </summary>
+		public static List<Toplevel> MdiChildes {
+			get {
+				if (MdiTop != null) {
+					List<Toplevel> mdiChildes = new List<Toplevel> ();
+					foreach (var top in toplevels) {
+						if (top != MdiTop && !top.Modal) {
+							mdiChildes.Add (top);
+						}
+					}
+					return mdiChildes;
+				}
+				return null;
+			}
+		}
+
+		/// <summary>
+		/// The <see cref="Toplevel"/> object used for the application on startup which <see cref="Toplevel.IsMdiContainer"/> is true.
+		/// </summary>
+		public static Toplevel MdiTop { get; private set; }
+
 		/// <summary>
 		/// The <see cref="Toplevel"/> object used for the application on startup (<seealso cref="Application.Top"/>)
 		/// </summary>
@@ -125,8 +150,6 @@ namespace Terminal.Gui {
 		/// <value>The main loop.</value>
 		public static MainLoop MainLoop { get; private set; }
 
-		static Stack<Toplevel> toplevels = new Stack<Toplevel> ();
-
 		/// <summary>
 		///   This event is raised on each iteration of the <see cref="MainLoop"/> 
 		/// </summary>
@@ -252,6 +275,9 @@ namespace Terminal.Gui {
 				SynchronizationContext.SetSynchronizationContext (new MainLoopSyncContext (MainLoop));
 			}
 			Top = topLevelFactory ();
+			if (Top.IsMdiContainer) {
+				MdiTop = Top;
+			}
 			Current = Top;
 			_initialized = true;
 		}
@@ -349,6 +375,72 @@ namespace Terminal.Gui {
 			}
 		}
 
+		static View FindDeepestTop (Toplevel start, int x, int y, out int resx, out int resy)
+		{
+			var startFrame = start.Frame;
+
+			if (!startFrame.Contains (x, y)) {
+				resx = 0;
+				resy = 0;
+				return null;
+			}
+
+			if (toplevels != null) {
+				int count = toplevels.Count;
+				if (count > 0) {
+					var rx = x - startFrame.X;
+					var ry = y - startFrame.Y;
+					foreach (var t in toplevels) {
+						if (t != Current) {
+							if (t != start && t.Visible && t.Frame.Contains (rx, ry)) {
+								start = t;
+								break;
+							}
+						}
+					}
+				}
+			}
+			resx = x - startFrame.X;
+			resy = y - startFrame.Y;
+			return start;
+		}
+
+		static View FindDeepestMdiView (View start, int x, int y, out int resx, out int resy)
+		{
+			if (start.GetType ().BaseType != typeof (Toplevel)
+				&& !((Toplevel)start).IsMdiContainer) {
+				resx = 0;
+				resy = 0;
+				return null;
+			}
+
+			var startFrame = start.Frame;
+
+			if (!startFrame.Contains (x, y)) {
+				resx = 0;
+				resy = 0;
+				return null;
+			}
+
+			int count = toplevels.Count;
+			for (int i = count - 1; i >= 0; i--) {
+				foreach (var top in toplevels) {
+					var rx = x - startFrame.X;
+					var ry = y - startFrame.Y;
+					if (top.Visible && top.Frame.Contains (rx, ry)) {
+						var deep = FindDeepestView (top, rx, ry, out resx, out resy);
+						if (deep == null)
+							return FindDeepestMdiView (top, rx, ry, out resx, out resy);
+						if (deep != MdiTop)
+							return deep;
+					}
+				}
+			}
+			resx = x - startFrame.X;
+			resy = y - startFrame.Y;
+			return start;
+		}
+
 		static View FindDeepestView (View start, int x, int y, out int resx, out int resy)
 		{
 			var startFrame = start.Frame;
@@ -380,6 +472,18 @@ namespace Terminal.Gui {
 			return start;
 		}
 
+		static View FindTopFromView (View view)
+		{
+			View top = view?.SuperView != null ? view.SuperView : view;
+
+			while (top?.SuperView != null) {
+				if (top?.SuperView != null) {
+					top = top.SuperView;
+				}
+			}
+			return top;
+		}
+
 		internal static View mouseGrabView;
 
 		/// <summary>
@@ -441,6 +545,17 @@ namespace Terminal.Gui {
 				}
 			}
 
+			if ((view == null || view == MdiTop) && !Current.Modal && MdiTop != null
+				&& me.Flags != MouseFlags.ReportMousePosition && me.Flags != 0) {
+
+				var top = FindDeepestTop (Top, me.X, me.Y, out _, out _);
+				view = FindDeepestView (top, me.X, me.Y, out rx, out ry);
+
+				if (view != null && view != MdiTop && top != Current) {
+					MoveCurrent ((Toplevel)top);
+				}
+			}
+
 			if (view != null) {
 				var nme = new MouseEvent () {
 					X = rx,
@@ -473,6 +588,56 @@ namespace Terminal.Gui {
 			}
 		}
 
+		// Only return true if the Current has changed.
+		static bool MoveCurrent (Toplevel top)
+		{
+			// The Current is modal and the top is not modal toplevel then
+			// the Current must be moved above the first not modal toplevel.
+			if (MdiTop != null && top != MdiTop && top != Current && Current?.Modal == true && !toplevels.Peek ().Modal) {
+				lock (toplevels) {
+					toplevels.MoveTo (Current, 0, new ToplevelEqualityComparer ());
+				}
+				var index = 0;
+				var savedToplevels = toplevels.ToArray ();
+				foreach (var t in savedToplevels) {
+					if (!t.Modal && t != Current && t != top && t != savedToplevels [index]) {
+						lock (toplevels) {
+							toplevels.MoveTo (top, index, new ToplevelEqualityComparer ());
+						}
+					}
+					index++;
+				}
+				return false;
+			}
+			// The Current and the top are both not running toplevel then
+			// the top must be moved above the first not running toplevel.
+			if (MdiTop != null && top != MdiTop && top != Current && Current?.Running == false && !top.Running) {
+				lock (toplevels) {
+					toplevels.MoveTo (Current, 0, new ToplevelEqualityComparer ());
+				}
+				var index = 0;
+				foreach (var t in toplevels.ToArray ()) {
+					if (!t.Running && t != Current && index > 0) {
+						lock (toplevels) {
+							toplevels.MoveTo (top, index - 1, new ToplevelEqualityComparer ());
+						}
+					}
+					index++;
+				}
+				return false;
+			}
+			if ((MdiTop != null && top?.Modal == true && toplevels.Peek () != top)
+				|| (MdiTop != null && Current != MdiTop && Current?.Modal == false && top == MdiTop)
+				|| (MdiTop != null && Current?.Modal == false && top != Current)
+				|| (MdiTop != null && Current?.Modal == true && top == MdiTop)) {
+				lock (toplevels) {
+					toplevels.MoveTo (top, 0, new ToplevelEqualityComparer ());
+					Current = top;
+				}
+			}
+			return true;
+		}
+
 		static bool OutsideFrame (Point p, Rect r)
 		{
 			return p.X < 0 || p.X > r.Width - 1 || p.Y < 0 || p.Y > r.Height - 1;
@@ -493,8 +658,12 @@ namespace Terminal.Gui {
 		/// </remarks>
 		public static RunState Begin (Toplevel toplevel)
 		{
-			if (toplevel == null)
+			if (toplevel == null) {
 				throw new ArgumentNullException (nameof (toplevel));
+			} else if (toplevel.IsMdiContainer && MdiTop != null) {
+				throw new InvalidOperationException ("Only one Mdi Container is allowed.");
+			}
+
 			var rs = new RunState (toplevel);
 
 			Init ();
@@ -506,18 +675,68 @@ namespace Terminal.Gui {
 				initializable.BeginInit ();
 				initializable.EndInit ();
 			}
-			toplevels.Push (toplevel);
-			Current = toplevel;
-			SetCurrentAsTop ();
+
+			lock (toplevels) {
+				if (string.IsNullOrEmpty (toplevel.Id.ToString ())) {
+					var count = 1;
+					var id = (toplevels.Count + count).ToString ();
+					while (toplevels.Count > 0 && toplevels.FirstOrDefault (x => x.Id.ToString () == id) != null) {
+						count++;
+						id = (toplevels.Count + count).ToString ();
+					}
+					toplevel.Id = (toplevels.Count + count).ToString ();
+
+					toplevels.Push (toplevel);
+				} else {
+					var dup = toplevels.FirstOrDefault (x => x.Id.ToString () == toplevel.Id);
+					if (dup == null) {
+						toplevels.Push (toplevel);
+					}
+				}
+
+				if (toplevels.FindDuplicates (new ToplevelEqualityComparer ()).Count > 0) {
+					throw new ArgumentException ("There are duplicates toplevels Id's");
+				}
+			}
+			if (toplevel.IsMdiContainer) {
+				MdiTop = toplevel;
+				Top = MdiTop;
+			}
+
+			var refreshDriver = true;
+			if (MdiTop == null || toplevel.IsMdiContainer || (Current?.Modal == false && toplevel.Modal)
+				|| (Current?.Modal == false && !toplevel.Modal) || (Current?.Modal == true && toplevel.Modal)) {
+
+				if (toplevel.Visible) {
+					Current = toplevel;
+					SetCurrentAsTop ();
+				} else {
+					refreshDriver = false;
+				}
+			} else if ((MdiTop != null && toplevel != MdiTop && Current?.Modal == true && !toplevels.Peek ().Modal)
+				|| (MdiTop != null && toplevel != MdiTop && Current?.Running == false)) {
+				refreshDriver = false;
+				MoveCurrent (toplevel);
+			} else {
+				refreshDriver = false;
+				MoveCurrent (Current);
+			}
+
 			Driver.PrepareToRun (MainLoop, ProcessKeyEvent, ProcessKeyDownEvent, ProcessKeyUpEvent, ProcessMouseEvent);
 			if (toplevel.LayoutStyle == LayoutStyle.Computed)
 				toplevel.SetRelativeLayout (new Rect (0, 0, Driver.Cols, Driver.Rows));
+			toplevel.PositionToplevels ();
 			toplevel.LayoutSubviews ();
 			toplevel.WillPresent ();
-			toplevel.OnLoaded ();
-			Redraw (toplevel);
-			toplevel.PositionCursor ();
-			Driver.Refresh ();
+			if (refreshDriver) {
+				if (MdiTop != null) {
+					MdiTop.OnChildLoaded (toplevel);
+				}
+				toplevel.OnLoaded ();
+				Redraw (toplevel);
+				toplevel.PositionCursor ();
+				Driver.Refresh ();
+			}
 
 			return rs;
 		}
@@ -531,7 +750,11 @@ namespace Terminal.Gui {
 			if (runState == null)
 				throw new ArgumentNullException (nameof (runState));
 
-			runState.Toplevel.OnUnloaded ();
+			if (MdiTop != null) {
+				MdiTop.OnChildUnloaded (runState.Toplevel);
+			} else {
+				runState.Toplevel.OnUnloaded ();
+			}
 			runState.Dispose ();
 		}
 
@@ -560,6 +783,7 @@ namespace Terminal.Gui {
 			toplevels.Clear ();
 			Current = null;
 			Top = null;
+			MdiTop = null;
 
 			MainLoop = null;
 			Driver?.End ();
@@ -597,8 +821,10 @@ namespace Terminal.Gui {
 			Driver.UpdateScreen ();
 			View last = null;
 			foreach (var v in toplevels.Reverse ()) {
-				v.SetNeedsDisplay ();
-				v.Redraw (v.Bounds);
+				if (v.Visible) {
+					v.SetNeedsDisplay ();
+					v.Redraw (v.Bounds);
+				}
 				last = v;
 			}
 			last?.PositionCursor ();
@@ -611,6 +837,19 @@ namespace Terminal.Gui {
 				throw new ArgumentException ("The view that you end with must be balanced");
 			toplevels.Pop ();
 
+			(view as Toplevel)?.OnClosed ((Toplevel)view);
+
+			if (MdiTop != null && !((Toplevel)view).Modal && view != MdiTop) {
+				MdiTop.OnChildClosed (view as Toplevel);
+			}
+
+			if (toplevels.Count == 1 && Current == MdiTop) {
+				MdiTop.OnAllChildClosed ();
+				if (!MdiTop.IsMdiContainer) {
+					MdiTop = null;
+				}
+			}
+
 			if (toplevels.Count == 0) {
 				Current = null;
 			} else {
@@ -648,17 +887,28 @@ namespace Terminal.Gui {
 					MainLoop.MainIteration ();
 					Iteration?.Invoke ();
 
+					EnsureModalAlwaysOnTop (state.Toplevel);
+					if ((state.Toplevel != Current && Current?.Modal == true)
+						|| (state.Toplevel != Current && Current?.Modal == false)) {
+						MdiTop?.OnDeactivate (state.Toplevel);
+						state.Toplevel = Current;
+						MdiTop?.OnActivate (state.Toplevel);
+						Top.SetChildNeedsDisplay ();
+						Refresh ();
+					}
 					if (Driver.EnsureCursorVisibility ()) {
 						state.Toplevel.SetNeedsDisplay ();
 					}
 				} else if (!wait) {
 					return;
 				}
-				if (state.Toplevel != Top && (!Top.NeedDisplay.IsEmpty || Top.ChildNeedsDisplay || Top.LayoutNeeded)) {
+				if (state.Toplevel != Top
+					&& (!Top.NeedDisplay.IsEmpty || Top.ChildNeedsDisplay || Top.LayoutNeeded)) {
 					Top.Redraw (Top.Bounds);
 					state.Toplevel.SetNeedsDisplay (state.Toplevel.Bounds);
 				}
-				if (!state.Toplevel.NeedDisplay.IsEmpty || state.Toplevel.ChildNeedsDisplay || state.Toplevel.LayoutNeeded) {
+				if (!state.Toplevel.NeedDisplay.IsEmpty || state.Toplevel.ChildNeedsDisplay || state.Toplevel.LayoutNeeded
+					|| MdiChildNeedsDisplay ()) {
 					state.Toplevel.Redraw (state.Toplevel.Bounds);
 					if (DebugDrawBounds) {
 						DrawBounds (state.Toplevel);
@@ -668,7 +918,40 @@ namespace Terminal.Gui {
 				} else {
 					Driver.UpdateCursor ();
 				}
+				if (state.Toplevel != Top && !state.Toplevel.Modal
+					&& (!Top.NeedDisplay.IsEmpty || Top.ChildNeedsDisplay || Top.LayoutNeeded)) {
+					Top.Redraw (Top.Bounds);
+				}
+			}
+		}
+
+		static void EnsureModalAlwaysOnTop (Toplevel toplevel)
+		{
+			if (!toplevel.Running || toplevel == Current || MdiTop == null || toplevels.Peek ().Modal) {
+				return;
+			}
+
+			foreach (var top in toplevels.Reverse ()) {
+				if (top.Modal && top != Current) {
+					MoveCurrent (top);
+					return;
+				}
+			}
+		}
+
+		static bool MdiChildNeedsDisplay ()
+		{
+			if (MdiTop == null) {
+				return false;
+			}
+
+			foreach (var top in toplevels) {
+				if (top != Current && top.Visible && (!top.NeedDisplay.IsEmpty || top.ChildNeedsDisplay || top.LayoutNeeded)) {
+					MdiTop.SetChildNeedsDisplay ();
+					return true;
+				}
 			}
+			return false;
 		}
 
 		internal static bool DebugDrawBounds = false;
@@ -698,14 +981,17 @@ namespace Terminal.Gui {
 			if (_initialized && Driver != null) {
 				var top = new T ();
 				if (top.GetType ().BaseType == typeof (Toplevel)) {
-					Top = top;
+					if (MdiTop == null) {
+						Top = top;
+					}
 				} else {
 					throw new ArgumentException (top.GetType ().BaseType.Name);
 				}
+				Run (top, errorHandler);
 			} else {
 				Init (() => new T ());
+				Run (Top, errorHandler);
 			}
-			Run (Top, errorHandler);
 		}
 
 		/// <summary>
@@ -735,7 +1021,7 @@ namespace Terminal.Gui {
 		///     When <paramref name="errorHandler"/> is null the exception is rethrown, when it returns true the application is resumed and when false method exits gracefully.
 		///   </para>
 		/// </remarks>
-		/// <param name="view">The <see cref="Toplevel"/> tu run modally.</param>
+		/// <param name="view">The <see cref="Toplevel"/> to run modally.</param>
 		/// <param name="errorHandler">Handler for any unhandled exceptions (resumes when returns true, rethrows when null).</param>
 		public static void Run (Toplevel view, Func<Exception, bool> errorHandler = null)
 		{
@@ -763,19 +1049,74 @@ namespace Terminal.Gui {
 		}
 
 		/// <summary>
-		/// Stops running the most recent <see cref="Toplevel"/>. 
+		/// Stops running the most recent <see cref="Toplevel"/> or the <paramref name="top"/> if provided.
 		/// </summary>
+		/// <param name="top">The toplevel to request stop.</param>
 		/// <remarks>
 		///   <para>
 		///   This will cause <see cref="Application.Run(Func{Exception, bool})"/> to return.
 		///   </para>
 		///   <para>
-		///     Calling <see cref="Application.RequestStop"/> is equivalent to setting the <see cref="Toplevel.Running"/> property on the curently running <see cref="Toplevel"/> to false.
+		///     Calling <see cref="Application.RequestStop"/> is equivalent to setting the <see cref="Toplevel.Running"/> property on the currently running <see cref="Toplevel"/> to false.
 		///   </para>
 		/// </remarks>
-		public static void RequestStop ()
+		public static void RequestStop (Toplevel top = null)
 		{
-			Current.Running = false;
+			if (MdiTop == null || top == null || (MdiTop == null && top != null)) {
+				top = Current;
+			}
+
+			if (MdiTop != null && top.IsMdiContainer && top?.Running == true
+				&& (Current?.Modal == false || (Current?.Modal == true && Current?.Running == false))) {
+
+				MdiTop.RequestStop ();
+			} else if (MdiTop != null && top != Current && Current?.Running == true && Current?.Modal == true
+				&& top.Modal && top.Running) {
+
+				var ev = new ToplevelClosingEventArgs (Current);
+				Current.OnClosing (ev);
+				if (ev.Cancel) {
+					return;
+				}
+				ev = new ToplevelClosingEventArgs (top);
+				top.OnClosing (ev);
+				if (ev.Cancel) {
+					return;
+				}
+				Current.Running = false;
+				top.Running = false;
+			} else if ((MdiTop != null && top != MdiTop && top != Current && Current?.Modal == false
+				&& Current?.Running == true && !top.Running)
+				|| (MdiTop != null && top != MdiTop && top != Current && Current?.Modal == false
+				&& Current?.Running == false && !top.Running && toplevels.ToArray () [1].Running)) {
+
+				MoveCurrent (top);
+			} else if (MdiTop != null && Current != top && Current?.Running == true && !top.Running
+				&& Current?.Modal == true && top.Modal) {
+				// The Current and the top are both modal so needed to set the Current.Running to false too.
+				Current.Running = false;
+			} else if (MdiTop != null && Current == top && MdiTop?.Running == true && Current?.Running == true && top.Running
+				&& Current?.Modal == true && top.Modal) {
+				// The MdiTop was requested to stop inside a modal toplevel which is the Current and top,
+				// both are the same, so needed to set the Current.Running to false too.
+				Current.Running = false;
+			} else {
+				Toplevel currentTop;
+				if (top == Current || (Current?.Modal == true && !top.Modal)) {
+					currentTop = Current;
+				} else {
+					currentTop = top;
+				}
+				if (!currentTop.Running) {
+					return;
+				}
+				var ev = new ToplevelClosingEventArgs (currentTop);
+				currentTop.OnClosing (ev);
+				if (ev.Cancel) {
+					return;
+				}
+				currentTop.Running = false;
+			}
 		}
 
 		/// <summary>
@@ -804,8 +1145,8 @@ namespace Terminal.Gui {
 			Resized?.Invoke (new ResizedEventArgs () { Cols = full.Width, Rows = full.Height });
 			Driver.Clip = full;
 			foreach (var t in toplevels) {
-				t.PositionToplevels ();
 				t.SetRelativeLayout (full);
+				t.PositionToplevels ();
 				t.LayoutSubviews ();
 			}
 			Refresh ();
@@ -813,22 +1154,74 @@ namespace Terminal.Gui {
 
 		static void SetToplevelsSize (Rect full)
 		{
-			foreach (var t in toplevels) {
-				if (t?.SuperView == null && !t.Modal) {
-					t.Frame = full;
-					t.Width = full.Width;
-					t.Height = full.Height;
+			if (MdiTop == null) {
+				foreach (var t in toplevels) {
+					if (t?.SuperView == null && !t.Modal) {
+						t.Frame = full;
+						t.Width = full.Width;
+						t.Height = full.Height;
+					}
 				}
+			} else {
+				Top.Frame = full;
+				Top.Width = full.Width;
+				Top.Height = full.Height;
 			}
 		}
 
 		static bool SetCurrentAsTop ()
 		{
-			if (Current != Top && Current?.SuperView == null && !Current.Modal) {
+			if (MdiTop == null && Current != Top && Current?.SuperView == null && Current?.Modal == false) {
 				Top = Current;
 				return true;
 			}
 			return false;
 		}
+
+		/// <summary>
+		/// Move to the next Mdi child from the <see cref="MdiTop"/>.
+		/// </summary>
+		public static void MoveNext ()
+		{
+			if (MdiTop != null && !Current.Modal) {
+				lock (toplevels) {
+					toplevels.MoveNext ();
+					while (toplevels.Peek () == MdiTop || !toplevels.Peek ().Visible) {
+						toplevels.MoveNext ();
+					}
+					Current = toplevels.Peek ();
+				}
+			}
+		}
+
+		/// <summary>
+		/// Move to the previous Mdi child from the <see cref="MdiTop"/>.
+		/// </summary>
+		public static void MovePrevious ()
+		{
+			if (MdiTop != null && !Current.Modal) {
+				lock (toplevels) {
+					toplevels.MovePrevious ();
+					while (toplevels.Peek () == MdiTop || !toplevels.Peek ().Visible) {
+						lock (toplevels) {
+							toplevels.MovePrevious ();
+						}
+					}
+					Current = toplevels.Peek ();
+				}
+			}
+		}
+
+		internal static bool ShowChild (Toplevel top)
+		{
+			if (top.Visible && MdiTop != null && Current?.Modal == false) {
+				lock (toplevels) {
+					toplevels.MoveTo (top, 0, new ToplevelEqualityComparer ());
+					Current = top;
+				}
+				return true;
+			}
+			return false;
+		}
 	}
 }

Terminal.Gui/Core/StackExtensions.cs

@@ -0,0 +1,196 @@
+using System;
+using System.Collections.Generic;
+
+namespace Terminal.Gui {
+	/// <summary>
+	/// Extension of <see cref="Stack{T}"/> helper to work with specific <see cref="IEqualityComparer{T}"/>
+	/// </summary>
+	public static class StackExtensions {
+		/// <summary>
+		/// Replaces an stack object values that match with the value to replace.
+		/// </summary>
+		/// <typeparam name="T">The stack object type.</typeparam>
+		/// <param name="stack">The stack object.</param>
+		/// <param name="valueToReplace">Value to replace.</param>
+		/// <param name="valueToReplaceWith">Value to replace with to what matches the value to replace.</param>
+		/// <param name="comparer">The comparison object.</param>
+		public static void Replace<T> (this Stack<T> stack, T valueToReplace,
+			T valueToReplaceWith, IEqualityComparer<T> comparer = null)
+		{
+			comparer = comparer ?? EqualityComparer<T>.Default;
+
+			var temp = new Stack<T> ();
+			while (stack.Count > 0) {
+				var value = stack.Pop ();
+				if (comparer.Equals (value, valueToReplace)) {
+					stack.Push (valueToReplaceWith);
+					break;
+				}
+				temp.Push (value);
+			}
+
+			while (temp.Count > 0)
+				stack.Push (temp.Pop ());
+		}
+
+		/// <summary>
+		/// Swap two stack objects values that matches with the both values.
+		/// </summary>
+		/// <typeparam name="T">The stack object type.</typeparam>
+		/// <param name="stack">The stack object.</param>
+		/// <param name="valueToSwapFrom">Value to swap from.</param>
+		/// <param name="valueToSwapTo">Value to swap to.</param>
+		/// <param name="comparer">The comparison object.</param>
+		public static void Swap<T> (this Stack<T> stack, T valueToSwapFrom,
+			T valueToSwapTo, IEqualityComparer<T> comparer = null)
+		{
+			comparer = comparer ?? EqualityComparer<T>.Default;
+
+			int index = stack.Count - 1;
+			T [] stackArr = new T [stack.Count];
+			while (stack.Count > 0) {
+				var value = stack.Pop ();
+				if (comparer.Equals (value, valueToSwapFrom)) {
+					stackArr [index] = valueToSwapTo;
+				} else if (comparer.Equals (value, valueToSwapTo)) {
+					stackArr [index] = valueToSwapFrom;
+				} else {
+					stackArr [index] = value;
+				}
+				index--;
+			}
+
+			for (int i = 0; i < stackArr.Length; i++)
+				stack.Push (stackArr [i]);
+		}
+
+		/// <summary>
+		/// Move the first stack object value to the end.
+		/// </summary>
+		/// <typeparam name="T">The stack object type.</typeparam>
+		/// <param name="stack">The stack object.</param>
+		public static void MoveNext<T> (this Stack<T> stack)
+		{
+			var temp = new Stack<T> ();
+			var last = stack.Pop ();
+			while (stack.Count > 0) {
+				var value = stack.Pop ();
+				temp.Push (value);
+			}
+			temp.Push (last);
+
+			while (temp.Count > 0)
+				stack.Push (temp.Pop ());
+		}
+
+		/// <summary>
+		/// Move the last stack object value to the top.
+		/// </summary>
+		/// <typeparam name="T">The stack object type.</typeparam>
+		/// <param name="stack">The stack object.</param>
+		public static void MovePrevious<T> (this Stack<T> stack)
+		{
+			var temp = new Stack<T> ();
+			T first = default;
+			while (stack.Count > 0) {
+				var value = stack.Pop ();
+				temp.Push (value);
+				if (stack.Count == 1) {
+					first = stack.Pop ();
+				}
+			}
+
+			while (temp.Count > 0)
+				stack.Push (temp.Pop ());
+			stack.Push (first);
+		}
+
+		/// <summary>
+		/// Find all duplicates stack objects values.
+		/// </summary>
+		/// <typeparam name="T">The stack object type.</typeparam>
+		/// <param name="stack">The stack object.</param>
+		/// <param name="comparer">The comparison object.</param>
+		/// <returns>The duplicates stack object.</returns>
+		public static Stack<T> FindDuplicates<T> (this Stack<T> stack, IEqualityComparer<T> comparer = null)
+		{
+			comparer = comparer ?? EqualityComparer<T>.Default;
+
+			var dup = new Stack<T> ();
+			T [] stackArr = stack.ToArray ();
+			for (int i = 0; i < stackArr.Length; i++) {
+				var value = stackArr [i];
+				for (int j = i + 1; j < stackArr.Length; j++) {
+					var valueToFind = stackArr [j];
+					if (comparer.Equals (value, valueToFind) && !Contains (dup, valueToFind)) {
+						dup.Push (value);
+					}
+				}
+			}
+
+			return dup;
+		}
+
+		/// <summary>
+		/// Check if the stack object contains the value to find.
+		/// </summary>
+		/// <typeparam name="T">The stack object type.</typeparam>
+		/// <param name="stack">The stack object.</param>
+		/// <param name="valueToFind">Value to find.</param>
+		/// <param name="comparer">The comparison object.</param>
+		/// <returns><c>true</c> If the value was found.<c>false</c> otherwise.</returns>
+		public static bool Contains<T> (this Stack<T> stack, T valueToFind, IEqualityComparer<T> comparer = null)
+		{
+			comparer = comparer ?? EqualityComparer<T>.Default;
+
+			foreach (T obj in stack) {
+				if (comparer.Equals (obj, valueToFind)) {
+					return true;
+				}
+			}
+			return false;
+		}
+
+		/// <summary>
+		/// Move the stack object value to the index.
+		/// </summary>
+		/// <typeparam name="T">The stack object type.</typeparam>
+		/// <param name="stack">The stack object.</param>
+		/// <param name="valueToMove">Value to move.</param>
+		/// <param name="index">The index where to move.</param>
+		/// <param name="comparer">The comparison object.</param>
+		public static void MoveTo<T> (this Stack<T> stack, T valueToMove, int index = 0,
+			IEqualityComparer<T> comparer = null)
+		{
+			if (index < 0) {
+				return;
+			}
+
+			comparer = comparer ?? EqualityComparer<T>.Default;
+
+			var temp = new Stack<T> ();
+			var toMove = default (T);
+			var stackCount = stack.Count;
+			var count = 0;
+			while (stack.Count > 0) {
+				var value = stack.Pop ();
+				if (comparer.Equals (value, valueToMove)) {
+					toMove = value;
+					break;
+				}
+				temp.Push (value);
+				count++;
+			}
+
+			int idx = 0;
+			while (stack.Count < stackCount) {
+				if (count - idx == index) {
+					stack.Push (toMove);
+				} else {
+					stack.Push (temp.Pop ());
+				}
+				idx++;
+			}
+		}
+	}
+}

Terminal.Gui/Core/Toplevel.cs

@@ -16,11 +16,11 @@ namespace Terminal.Gui {
 	/// <remarks>
 	///   <para>
 	///     Toplevels can be modally executing views, started by calling <see cref="Application.Run(Toplevel, Func{Exception, bool})"/>. 
-	///     They return control to the caller when <see cref="Application.RequestStop()"/> has 
+	///     They return control to the caller when <see cref="Application.RequestStop(Toplevel)"/> has 
 	///     been called (which sets the <see cref="Toplevel.Running"/> property to false). 
 	///   </para>
 	///   <para>
-	///     A Toplevel is created when an application initialzies Terminal.Gui by callling <see cref="Application.Init(ConsoleDriver, IMainLoopDriver)"/>.
+	///     A Toplevel is created when an application initializes Terminal.Gui by calling <see cref="Application.Init(ConsoleDriver, IMainLoopDriver)"/>.
 	///     The application Toplevel can be accessed via <see cref="Application.Top"/>. Additional Toplevels can be created 
 	///     and run (e.g. <see cref="Dialog"/>s. To run a Toplevel, create the <see cref="Toplevel"/> and 
 	///     call <see cref="Application.Run(Toplevel, Func{Exception, bool})"/>.
@@ -67,6 +67,90 @@ namespace Terminal.Gui {
 		/// </summary>
 		public event Action Unloaded;
 
+		/// <summary>
+		/// Invoked once the Toplevel's <see cref="Application.RunState"/> becomes the <see cref="Application.Current"/>.
+		/// </summary>
+		public event Action<Toplevel> Activate;
+
+		/// <summary>
+		/// Invoked once the Toplevel's <see cref="Application.RunState"/> ceases to be the <see cref="Application.Current"/>.
+		/// </summary>
+		public event Action<Toplevel> Deactivate;
+
+		/// <summary>
+		/// Invoked once the child Toplevel's <see cref="Application.RunState"/> is closed from the <see cref="Application.End(View)"/>
+		/// </summary>
+		public event Action<Toplevel> ChildClosed;
+
+		/// <summary>
+		/// Invoked once the last child Toplevel's <see cref="Application.RunState"/> is closed from the <see cref="Application.End(View)"/>
+		/// </summary>
+		public event Action AllChildClosed;
+
+		/// <summary>
+		/// Invoked once the Toplevel's <see cref="Application.RunState"/> is being closing from the <see cref="Application.RequestStop(Toplevel)"/>
+		/// </summary>
+		public event Action<ToplevelClosingEventArgs> Closing;
+
+		/// <summary>
+		/// Invoked once the Toplevel's <see cref="Application.RunState"/> is closed from the <see cref="Application.End(View)"/>
+		/// </summary>
+		public event Action<Toplevel> Closed;
+
+		/// <summary>
+		/// Invoked once the child Toplevel's <see cref="Application.RunState"/> has begin loaded.
+		/// </summary>
+		public event Action<Toplevel> ChildLoaded;
+
+		/// <summary>
+		/// Invoked once the child Toplevel's <see cref="Application.RunState"/> has begin unloaded.
+		/// </summary>
+		public event Action<Toplevel> ChildUnloaded;
+
+		internal virtual void OnChildUnloaded (Toplevel top)
+		{
+			ChildUnloaded?.Invoke (top);
+		}
+
+		internal virtual void OnChildLoaded (Toplevel top)
+		{
+			ChildLoaded?.Invoke (top);
+		}
+
+		internal virtual void OnClosed (Toplevel top)
+		{
+			Closed?.Invoke (top);
+		}
+
+		internal virtual bool OnClosing (ToplevelClosingEventArgs ev)
+		{
+			Closing?.Invoke (ev);
+			return ev.Cancel;
+		}
+
+		internal virtual void OnAllChildClosed ()
+		{
+			AllChildClosed?.Invoke ();
+		}
+
+		internal virtual void OnChildClosed (Toplevel top)
+		{
+			if (IsMdiContainer) {
+				SetChildNeedsDisplay ();
+			}
+			ChildClosed?.Invoke (top);
+		}
+
+		internal virtual void OnDeactivate (Toplevel activated)
+		{
+			Deactivate?.Invoke (activated);
+		}
+
+		internal virtual void OnActivate (Toplevel deactivated)
+		{
+			Activate?.Invoke (deactivated);
+		}
+
 		/// <summary>
 		/// Called from <see cref="Application.Begin(Toplevel)"/> before the <see cref="Toplevel"/> is redraws for the first time.
 		/// </summary>
@@ -149,6 +233,20 @@ namespace Terminal.Gui {
 		/// </summary>
 		public virtual StatusBar StatusBar { get; set; }
 
+		/// <summary>
+		/// Gets or sets if this Toplevel is a Mdi container.
+		/// </summary>
+		public bool IsMdiContainer { get; set; }
+
+		/// <summary>
+		/// Gets or sets if this Toplevel is a Mdi child.
+		/// </summary>
+		public bool IsMdiChild {
+			get {
+				return Application.MdiTop != null && Application.MdiTop != this && !Modal;
+			}
+		}
+
 		///<inheritdoc/>
 		public override bool OnKeyDown (KeyEvent keyEvent)
 		{
@@ -198,7 +296,11 @@ namespace Terminal.Gui {
 			switch (ShortcutHelper.GetModifiersKey (keyEvent)) {
 			case Key.Q | Key.CtrlMask:
 				// FIXED: stop current execution of this container
-				Application.RequestStop ();
+				if (Application.MdiTop != null) {
+					Application.MdiTop.RequestStop ();
+				} else {
+					Application.RequestStop ();
+				}
 				break;
 			case Key.Z | Key.CtrlMask:
 				Driver.Suspend ();
@@ -239,16 +341,26 @@ namespace Terminal.Gui {
 				return true;
 			case Key.Tab | Key.CtrlMask:
 			case Key key when key == Application.AlternateForwardKey: // Needed on Unix
-				Application.Top.FocusNext ();
-				if (Application.Top.Focused == null) {
+				if (Application.MdiTop == null) {
 					Application.Top.FocusNext ();
+					if (Application.Top.Focused == null) {
+						Application.Top.FocusNext ();
+					}
+					Application.Top.SetNeedsDisplay ();
+				} else {
+					MoveNext ();
 				}
 				return true;
 			case Key.Tab | Key.ShiftMask | Key.CtrlMask:
 			case Key key when key == Application.AlternateBackwardKey: // Needed on Unix
-				Application.Top.FocusPrev ();
-				if (Application.Top.Focused == null) {
+				if (Application.MdiTop == null) {
 					Application.Top.FocusPrev ();
+					if (Application.Top.Focused == null) {
+						Application.Top.FocusPrev ();
+					}
+					Application.Top.SetNeedsDisplay ();
+				} else {
+					MovePrevious ();
 				}
 				return true;
 			case Key.L | Key.CtrlMask:
@@ -383,7 +495,7 @@ namespace Terminal.Gui {
 			//System.Diagnostics.Debug.WriteLine ($"nx:{nx}, rWidth:{rWidth}");
 			bool m, s;
 			if (SuperView == null || SuperView.GetType () != typeof (Toplevel)) {
-				m = Application.Top.MenuBar != null;
+				m = Application.MdiTop?.MenuBar != null || Application.Top.MenuBar != null;
 			} else {
 				m = ((Toplevel)SuperView).MenuBar != null;
 			}
@@ -394,7 +506,9 @@ namespace Terminal.Gui {
 			}
 			ny = Math.Max (y, l);
 			if (SuperView == null || SuperView.GetType () != typeof (Toplevel)) {
-				s = Application.Top.StatusBar != null && Application.Top.StatusBar.Visible;
+				s = (Application.MdiTop != null && Application.MdiTop.StatusBar != null
+					&& Application.MdiTop.StatusBar.Visible)
+					|| (Application.Top.StatusBar != null && Application.Top.StatusBar.Visible);
 			} else {
 				s = ((Toplevel)SuperView).StatusBar != null && ((Toplevel)SuperView).StatusBar.Visible;
 			}
@@ -429,7 +543,8 @@ namespace Terminal.Gui {
 		public virtual void PositionToplevel (Toplevel top)
 		{
 			EnsureVisibleBounds (top, top.Frame.X, top.Frame.Y, out int nx, out int ny);
-			if (top?.SuperView != null && (nx != top.Frame.X || ny != top.Frame.Y) && top.LayoutStyle == LayoutStyle.Computed) {
+			if ((top?.SuperView != null || Application.MdiTop != null && top != Application.MdiTop)
+				&& (nx > top.Frame.X || ny > top.Frame.Y) && top.LayoutStyle == LayoutStyle.Computed) {
 				if ((top.X == null || top.X is Pos.PosAbsolute) && top.Bounds.X != nx) {
 					top.X = nx;
 				}
@@ -437,16 +552,28 @@ namespace Terminal.Gui {
 					top.Y = ny;
 				}
 			}
-			var statusBar = top?.SuperView != null && top.SuperView is Toplevel toplevel
-				? toplevel.StatusBar : null;
 
+			View superView = null;
+			StatusBar statusBar = null;
+
+			if (top != Application.MdiTop && Application.MdiTop != null && Application.MdiTop.StatusBar != null) {
+				superView = Application.MdiTop;
+				statusBar = Application.MdiTop.StatusBar;
+			} else if (top?.SuperView != null && top.SuperView is Toplevel toplevel) {
+				superView = top.SuperView;
+				statusBar = toplevel.StatusBar;
+			}
 			if (statusBar != null) {
-				if (ny + top.Frame.Height != top.SuperView.Frame.Height - (statusBar.Visible ? 1 : 0)) {
+				if (ny + top.Frame.Height >= superView.Frame.Height - (statusBar.Visible ? 1 : 0)) {
 					if (top.Height is Dim.DimFill) {
 						top.Height = Dim.Fill (statusBar.Visible ? 1 : 0);
 					}
 				}
-				top.SuperView.LayoutSubviews ();
+				if (superView == Application.MdiTop) {
+					top.SetRelativeLayout (superView.Frame);
+				} else {
+					superView.LayoutSubviews ();
+				}
 			}
 			if (top.StatusBar != null) {
 				if (top.StatusBar.Frame.Y != top.Frame.Height - (top.StatusBar.Visible ? 1 : 0)) {
@@ -460,30 +587,151 @@ namespace Terminal.Gui {
 		///<inheritdoc/>
 		public override void Redraw (Rect bounds)
 		{
-			if (IsCurrentTop || this == Application.Top || Application.Current.GetType ().BaseType == typeof (Toplevel)) {
-				if (!NeedDisplay.IsEmpty || LayoutNeeded) {
-					Driver.SetAttribute (Colors.TopLevel.Normal);
+			if (this == Application.MdiTop) {
+				RedrawMdi (bounds);
+			} else {
+				if (!CanBeVisible (this)) {
+					return;
+				}
+
+				if (!NeedDisplay.IsEmpty || ChildNeedsDisplay || LayoutNeeded) {
+					Driver.SetAttribute (ColorScheme.Normal);
 
 					// This is the Application.Top. Clear just the region we're being asked to redraw 
 					// (the bounds passed to us).
 					// Must be the screen-relative region to clear, not the bounds.
 					Clear (Frame);
 					Driver.SetAttribute (Colors.Base.Normal);
-					PositionToplevels ();
+				}
+			}
 
-					foreach (var view in Subviews) {
-						if (view.Frame.IntersectsWith (bounds)) {
-							view.SetNeedsLayout ();
-							view.SetNeedsDisplay (view.Bounds);
+			if (LayoutStyle == LayoutStyle.Computed)
+				SetRelativeLayout (Bounds);
+			PositionToplevels ();
+			LayoutSubviews ();
+
+			foreach (var view in Subviews) {
+				if (view.Frame.IntersectsWith (bounds) && !OutsideTopFrame (this)) {
+					view.SetNeedsLayout ();
+					view.SetNeedsDisplay (view.Bounds);
+					view.Redraw (view.Bounds);
+				}
+			}
+
+			ClearLayoutNeeded ();
+			ClearNeedsDisplay ();
+		}
+
+		void RedrawMdi (Rect bounds)
+		{
+			if (!IsMdiContainer) {
+				return;
+			}
+
+			if (!NeedDisplay.IsEmpty || ChildNeedsDisplay || LayoutNeeded) {
+				Driver.SetAttribute (ColorScheme.Normal);
+
+				Clear (Frame);
+
+				Driver.SetAttribute (Colors.Base.Normal);
+
+				if (LayoutStyle == LayoutStyle.Computed)
+					SetRelativeLayout (Bounds);
+				PositionToplevels ();
+				LayoutSubviews ();
+
+				foreach (var top in Application.MdiChildes.AsEnumerable ().Reverse ()) {
+					if (top.Frame.IntersectsWith (bounds)) {
+						if (top != this && !top.IsCurrentTop && !OutsideTopFrame (top) && top.Visible) {
+							top.SetNeedsLayout ();
+							top.SetNeedsDisplay (top.Bounds);
+							top.Redraw (top.Bounds);
 						}
 					}
+				}
+
+				ClearLayoutNeeded ();
+				ClearNeedsDisplay ();
+			}
+		}
+
+		bool OutsideTopFrame (Toplevel top)
+		{
+			if (top.Frame.X > Driver.Cols || top.Frame.Y > Driver.Rows) {
+				return true;
+			}
+			return false;
+		}
+
+		//
+		// FIXED:It does not look like the event is raised on clicked-drag
+		// need to figure that out.
+		//
+		internal static Point? dragPosition;
+		Point start;
+
+		///<inheritdoc/>
+		public override bool MouseEvent (MouseEvent mouseEvent)
+		{
+			// FIXED:The code is currently disabled, because the
+			// Driver.UncookMouse does not seem to have an effect if there is
+			// a pending mouse event activated.
+
+			int nx, ny;
+			if (!dragPosition.HasValue && mouseEvent.Flags == (MouseFlags.Button1Pressed)) {
+				// Only start grabbing if the user clicks on the title bar.
+				if (mouseEvent.Y == 0) {
+					start = new Point (mouseEvent.X, mouseEvent.Y);
+					dragPosition = new Point ();
+					nx = mouseEvent.X - mouseEvent.OfX;
+					ny = mouseEvent.Y - mouseEvent.OfY;
+					dragPosition = new Point (nx, ny);
+					Application.GrabMouse (this);
+				}
+
+				//System.Diagnostics.Debug.WriteLine ($"Starting at {dragPosition}");
+				return true;
+			} else if (mouseEvent.Flags == (MouseFlags.Button1Pressed | MouseFlags.ReportMousePosition) ||
+				mouseEvent.Flags == MouseFlags.Button3Pressed) {
+				if (dragPosition.HasValue) {
+					if (SuperView == null) {
+						// Redraw the entire app window using just our Frame. Since we are 
+						// Application.Top, and our Frame always == our Bounds (Location is always (0,0))
+						// our Frame is actually view-relative (which is what Redraw takes).
+						// We need to pass all the view bounds because since the windows was 
+						// moved around, we don't know exactly what was the affected region.
+						Application.Top.SetNeedsDisplay ();
+					} else {
+						SuperView.SetNeedsDisplay ();
+					}
+					EnsureVisibleBounds (this, mouseEvent.X + (SuperView == null ? mouseEvent.OfX - start.X : Frame.X - start.X),
+						mouseEvent.Y + (SuperView == null ? mouseEvent.OfY : Frame.Y), out nx, out ny);
+
+					dragPosition = new Point (nx, ny);
+					LayoutSubviews ();
+					Frame = new Rect (nx, ny, Frame.Width, Frame.Height);
+					if (X == null || X is Pos.PosAbsolute) {
+						X = nx;
+					}
+					if (Y == null || Y is Pos.PosAbsolute) {
+						Y = ny;
+					}
+					//System.Diagnostics.Debug.WriteLine ($"nx:{nx},ny:{ny}");
 
-					ClearLayoutNeeded ();
-					ClearNeedsDisplay ();
+					// FIXED: optimize, only SetNeedsDisplay on the before/after regions.
+					SetNeedsDisplay ();
+					return true;
 				}
 			}
 
-			base.Redraw (base.Bounds);
+			if (mouseEvent.Flags == MouseFlags.Button1Released && dragPosition.HasValue) {
+				Application.UngrabMouse ();
+				Driver.UncookMouse ();
+				dragPosition = null;
+			}
+
+			//System.Diagnostics.Debug.WriteLine (mouseEvent.ToString ());
+			return false;
 		}
 
 		/// <summary>
@@ -494,5 +742,209 @@ namespace Terminal.Gui {
 		{
 			FocusFirst ();
 		}
+
+		/// <summary>
+		/// Move to the next Mdi child from the <see cref="Application.MdiTop"/>.
+		/// </summary>
+		public virtual void MoveNext ()
+		{
+			Application.MoveNext ();
+		}
+
+		/// <summary>
+		/// Move to the previous Mdi child from the <see cref="Application.MdiTop"/>.
+		/// </summary>
+		public virtual void MovePrevious ()
+		{
+			Application.MovePrevious ();
+		}
+
+		/// <summary>
+		/// Stops running this <see cref="Toplevel"/>.
+		/// </summary>
+		public virtual void RequestStop ()
+		{
+			if (IsMdiContainer && Running
+				&& (Application.Current == this
+				|| Application.Current?.Modal == false
+				|| Application.Current?.Modal == true && Application.Current?.Running == false)) {
+
+				foreach (var child in Application.MdiChildes) {
+					var ev = new ToplevelClosingEventArgs (this);
+					if (child.OnClosing (ev)) {
+						return;
+					}
+					child.Running = false;
+					Application.RequestStop (child);
+				}
+				Running = false;
+				Application.RequestStop (this);
+			} else if (IsMdiContainer && Running && Application.Current?.Modal == true && Application.Current?.Running == true) {
+				var ev = new ToplevelClosingEventArgs (Application.Current);
+				if (OnClosing (ev)) {
+					return;
+				}
+				Application.RequestStop (Application.Current);
+			} else if (!IsMdiContainer && Running && (!Modal || (Modal && Application.Current != this))) {
+				var ev = new ToplevelClosingEventArgs (this);
+				if (OnClosing (ev)) {
+					return;
+				}
+				Running = false;
+				Application.RequestStop (this);
+			} else {
+				Application.RequestStop (Application.Current);
+			}
+		}
+
+		/// <summary>
+		/// Stops running the <paramref name="top"/> <see cref="Toplevel"/>.
+		/// </summary>
+		/// <param name="top">The toplevel to request stop.</param>
+		public virtual void RequestStop (Toplevel top)
+		{
+			top.RequestStop ();
+		}
+
+		///<inheritdoc/>
+		public override void PositionCursor ()
+		{
+			if (!IsMdiContainer) {
+				base.PositionCursor ();
+				return;
+			}
+
+			if (Focused == null) {
+				foreach (var top in Application.MdiChildes) {
+					if (top != this && top.Visible) {
+						top.SetFocus ();
+						return;
+					}
+				}
+			}
+			base.PositionCursor ();
+		}
+
+		/// <summary>
+		/// Gets the current visible toplevel Mdi child that match the arguments pattern.
+		/// </summary>
+		/// <param name="type">The type.</param>
+		/// <param name="exclude">The strings to exclude.</param>
+		/// <returns>The matched view.</returns>
+		public View GetTopMdiChild (Type type = null, string [] exclude = null)
+		{
+			if (Application.MdiTop == null) {
+				return null;
+			}
+
+			foreach (var top in Application.MdiChildes) {
+				if (type != null && top.GetType () == type
+					&& exclude?.Contains (top.Data.ToString ()) == false) {
+					return top;
+				} else if ((type != null && top.GetType () != type)
+					|| (exclude?.Contains (top.Data.ToString ()) == true)) {
+					continue;
+				}
+				return top;
+			}
+			return null;
+		}
+
+		/// <summary>
+		/// Shows the Mdi child indicated by the <paramref name="top"/> setting as <see cref="Application.Current"/>.
+		/// </summary>
+		/// <param name="top">The toplevel.</param>
+		/// <returns><see langword="true"/> if the toplevel can be showed.<see langword="false"/> otherwise.</returns>
+		public virtual bool ShowChild (Toplevel top = null)
+		{
+			if (Application.MdiTop != null) {
+				return Application.ShowChild (top == null ? this : top);
+			}
+			return false;
+		}
+	}
+
+	/// <summary>
+	/// Implements the <see cref="IEqualityComparer{T}"/> to comparing two <see cref="Toplevel"/> used by <see cref="StackExtensions"/>.
+	/// </summary>
+	public class ToplevelEqualityComparer : IEqualityComparer<Toplevel> {
+		/// <summary>Determines whether the specified objects are equal.</summary>
+		/// <param name="x">The first object of type <see cref="Toplevel" /> to compare.</param>
+		/// <param name="y">The second object of type <see cref="Toplevel" /> to compare.</param>
+		/// <returns>
+		///     <see langword="true" /> if the specified objects are equal; otherwise, <see langword="false" />.</returns>
+		public bool Equals (Toplevel x, Toplevel y)
+		{
+			if (y == null && x == null)
+				return true;
+			else if (x == null || y == null)
+				return false;
+			else if (x.Id == y.Id)
+				return true;
+			else
+				return false;
+		}
+
+		/// <summary>Returns a hash code for the specified object.</summary>
+		/// <param name="obj">The <see cref="Toplevel" /> for which a hash code is to be returned.</param>
+		/// <returns>A hash code for the specified object.</returns>
+		/// <exception cref="ArgumentNullException">The type of <paramref name="obj" /> is a reference type and <paramref name="obj" /> is <see langword="null" />.</exception>
+		public int GetHashCode (Toplevel obj)
+		{
+			if (obj == null)
+				throw new ArgumentNullException ();
+
+			int hCode = 0;
+			if (int.TryParse (obj.Id.ToString (), out int result)) {
+				hCode = result;
+			}
+			return hCode.GetHashCode ();
+		}
+	}
+
+	/// <summary>
+	/// Implements the <see cref="IComparer{T}"/> to sort the <see cref="Toplevel"/> from the <see cref="Application.MdiChildes"/> if needed.
+	/// </summary>
+	public sealed class ToplevelComparer : IComparer<Toplevel> {
+		/// <summary>Compares two objects and returns a value indicating whether one is less than, equal to, or greater than the other.</summary>
+		/// <param name="x">The first object to compare.</param>
+		/// <param name="y">The second object to compare.</param>
+		/// <returns>A signed integer that indicates the relative values of <paramref name="x" /> and <paramref name="y" />, as shown in the following table.Value Meaning Less than zero
+		///             <paramref name="x" /> is less than <paramref name="y" />.Zero
+		///             <paramref name="x" /> equals <paramref name="y" />.Greater than zero
+		///             <paramref name="x" /> is greater than <paramref name="y" />.</returns>
+		public int Compare (Toplevel x, Toplevel y)
+		{
+			if (ReferenceEquals (x, y))
+				return 0;
+			else if (x == null)
+				return -1;
+			else if (y == null)
+				return 1;
+			else
+				return string.Compare (x.Id.ToString (), y.Id.ToString ());
+		}
+	}
+	/// <summary>
+	/// <see cref="EventArgs"/> implementation for the <see cref="Toplevel.Closing"/> event.
+	/// </summary>
+	public class ToplevelClosingEventArgs : EventArgs {
+		/// <summary>
+		/// The toplevel requesting stop.
+		/// </summary>
+		public View RequestingTop { get; }
+		/// <summary>
+		/// Provides an event cancellation option.
+		/// </summary>
+		public bool Cancel { get; set; }
+
+		/// <summary>
+		/// Initializes the event arguments with the requesting toplevel.
+		/// </summary>
+		/// <param name="requestingTop">The <see cref="RequestingTop"/>.</param>
+		public ToplevelClosingEventArgs (Toplevel requestingTop)
+		{
+			RequestingTop = requestingTop;
+		}
 	}
 }

Terminal.Gui/Core/View.cs

@@ -268,7 +268,7 @@ namespace Terminal.Gui {
 			}
 		}
 
-		private int GetTabIndex (int idx)
+		int GetTabIndex (int idx)
 		{
 			int i = 0;
 			foreach (var v in SuperView.tabIndexes) {
@@ -280,7 +280,7 @@ namespace Terminal.Gui {
 			return Math.Min (i, idx);
 		}
 
-		private void SetTabIndex ()
+		void SetTabIndex ()
 		{
 			int i = 0;
 			foreach (var v in SuperView.tabIndexes) {
@@ -989,8 +989,8 @@ namespace Terminal.Gui {
 		internal void ViewToScreen (int col, int row, out int rcol, out int rrow, bool clipped = true)
 		{
 			// Computes the real row, col relative to the screen.
-			rrow = row + frame.Y;
-			rcol = col + frame.X;
+			rrow = Math.Max (row + frame.Y, 0);
+			rcol = Math.Max (col + frame.X, 0);
 			var ccontainer = container;
 			while (ccontainer != null) {
 				rrow += ccontainer.frame.Y;
@@ -1338,18 +1338,7 @@ namespace Terminal.Gui {
 
 			var clipRect = new Rect (Point.Empty, frame.Size);
 
-			if (ColorScheme != null) {
-				Driver.SetAttribute (HasFocus ? ColorScheme.Focus : ColorScheme.Normal);
-			}
-
-			if (!ustring.IsNullOrEmpty (Text)) {
-				Clear ();
-				// Draw any Text
-				if (textFormatter != null) {
-					textFormatter.NeedsFormat = true;
-				}
-				textFormatter?.Draw (ViewToScreen (Bounds), HasFocus ? ColorScheme.Focus : ColorScheme.Normal, HasFocus ? ColorScheme.HotFocus : ColorScheme.HotNormal);
-			}
+			DrawText ();
 
 			// Invoke DrawContentEvent
 			OnDrawContent (bounds);
@@ -1377,6 +1366,33 @@ namespace Terminal.Gui {
 			ClearNeedsDisplay ();
 		}
 
+		void DrawText ()
+		{
+			if (ColorScheme != null) {
+				Driver.SetAttribute (HasFocus ? ColorScheme.Focus : ColorScheme.Normal);
+			}
+
+			if (!ustring.IsNullOrEmpty (Text)) {
+				var savedClip = ClipToBounds ();
+				Rect viewBounds = Bounds;
+				if (SuperView != null && viewBounds.Width > SuperView.Bounds.Width) {
+					viewBounds.Width = SuperView.Bounds.Width;
+				}
+				if (SuperView != null && viewBounds.Height > SuperView.Bounds.Height) {
+					viewBounds.Height = SuperView.Bounds.Height;
+				}
+				var viewFrame = ViewToScreen (viewBounds);
+				Clear (viewFrame);
+				// Draw any Text
+				if (textFormatter != null) {
+					textFormatter.NeedsFormat = true;
+				}
+				textFormatter?.Draw (viewFrame, HasFocus ? ColorScheme.Focus : ColorScheme.Normal, HasFocus ? ColorScheme.HotFocus : ColorScheme.HotNormal);
+
+				Driver.Clip = savedClip;
+			}
+		}
+
 		/// <summary>
 		/// Event invoked when the content area of the View is to be drawn.
 		/// </summary>
@@ -1957,8 +1973,9 @@ namespace Terminal.Gui {
 				v.LayoutNeeded = false;
 			}
 
-			if (SuperView == Application.Top && LayoutNeeded && ordered.Count == 0 && LayoutStyle == LayoutStyle.Computed) {
-				SetRelativeLayout (Frame);
+			if (SuperView != null && SuperView == Application.Top && LayoutNeeded
+				&& ordered.Count == 0 && LayoutStyle == LayoutStyle.Computed) {
+				SetRelativeLayout (SuperView.Frame);
 			}
 
 			LayoutNeeded = false;
@@ -2259,7 +2276,7 @@ namespace Terminal.Gui {
 		/// </summary>
 		public bool Visible { get; set; } = true;
 
-		bool CanBeVisible (View view)
+		internal bool CanBeVisible (View view)
 		{
 			if (!view.Visible) {
 				return false;

Terminal.Gui/Core/Window.cs

@@ -209,77 +209,6 @@ namespace Terminal.Gui {
 			}
 		}
 
-		//
-		// FIXED:It does not look like the event is raised on clicked-drag
-		// need to figure that out.
-		//
-		internal static Point? dragPosition;
-		Point start;
-
-		///<inheritdoc/>
-		public override bool MouseEvent (MouseEvent mouseEvent)
-		{
-			// FIXED:The code is currently disabled, because the
-			// Driver.UncookMouse does not seem to have an effect if there is
-			// a pending mouse event activated.
-
-			int nx, ny;
-			if (!dragPosition.HasValue && (mouseEvent.Flags == MouseFlags.Button1Pressed
-				|| mouseEvent.Flags == (MouseFlags.Button1Pressed | MouseFlags.ReportMousePosition))) {
-				// Only start grabbing if the user clicks on the title bar.
-				if (mouseEvent.Y == 0) {
-					start = new Point (mouseEvent.X, mouseEvent.Y);
-					dragPosition = new Point ();
-					nx = mouseEvent.X - mouseEvent.OfX;
-					ny = mouseEvent.Y - mouseEvent.OfY;
-					dragPosition = new Point (nx, ny);
-					Application.GrabMouse (this);
-				}
-
-				//System.Diagnostics.Debug.WriteLine ($"Starting at {dragPosition}");
-				return true;
-			} else if (mouseEvent.Flags == (MouseFlags.Button1Pressed | MouseFlags.ReportMousePosition) ||
-				mouseEvent.Flags == MouseFlags.Button3Pressed) {
-				if (dragPosition.HasValue) {
-					if (SuperView == null) {
-						Application.Top.SetNeedsDisplay (Frame);
-						// Redraw the entire app window using just our Frame. Since we are 
-						// Application.Top, and our Frame always == our Bounds (Location is always (0,0))
-						// our Frame is actually view-relative (which is what Redraw takes).
-						Application.Top.Redraw (Frame);
-					} else {
-						SuperView.SetNeedsDisplay (Frame);
-					}
-					EnsureVisibleBounds (this, mouseEvent.X + (SuperView == null ? mouseEvent.OfX - start.X : Frame.X - start.X),
-						mouseEvent.Y + (SuperView == null ? mouseEvent.OfY : Frame.Y), out nx, out ny);
-
-					dragPosition = new Point (nx, ny);
-					LayoutSubviews ();
-					Frame = new Rect (nx, ny, Frame.Width, Frame.Height);
-					if (X == null || X is Pos.PosAbsolute) {
-						X = nx;
-					}
-					if (Y == null || Y is Pos.PosAbsolute) {
-						Y = ny;
-					}
-					//System.Diagnostics.Debug.WriteLine ($"nx:{nx},ny:{ny}");
-
-					// FIXED: optimize, only SetNeedsDisplay on the before/after regions.
-					SetNeedsDisplay ();
-					return true;
-				}
-			}
-
-			if (mouseEvent.Flags == MouseFlags.Button1Released && dragPosition.HasValue) {
-				Application.UngrabMouse ();
-				Driver.UncookMouse ();
-				dragPosition = null;
-			}
-
-			//System.Diagnostics.Debug.WriteLine (mouseEvent.ToString ());
-			return false;
-		}
-
 		/// <summary>
 		///   The text displayed by the <see cref="Label"/>.
 		/// </summary>