Adds a uniqueness semantic to the navigation history, by removing the previous state (by the selected nodes) from the prior history.

ILSpy/ILSpy.csproj

@@ -120,6 +120,7 @@
     <Compile Include="LoadedAssembly.cs" />
     <Compile Include="NativeMethods.cs" />
     <Compile Include="NavigationHistory.cs" />
+    <Compile Include="NavigationState.cs" />
     <Compile Include="OpenFromGacDialog.xaml.cs">
       <DependentUpon>OpenFromGacDialog.xaml</DependentUpon>
       <SubType>Code</SubType>
@@ -272,4 +273,4 @@
     <Folder Include="XmlDoc" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.Targets" />
-</Project>
+</Project>

ILSpy/MainWindow.xaml.cs

@@ -46,8 +46,7 @@ namespace ICSharpCode.ILSpy
 	/// </summary>
 	partial class MainWindow : Window
 	{
-		NavigationHistory<Tuple<List<SharpTreeNode>, DecompilerTextViewState>> history =
-			new NavigationHistory<Tuple<List<SharpTreeNode>, DecompilerTextViewState>>();
+		NavigationHistory<NavigationState> history = new NavigationHistory<NavigationState>();
 		ILSpySettings spySettings;
 		SessionSettings sessionSettings;
 		AssemblyListManager assemblyListManager;
@@ -334,7 +333,7 @@ namespace ICSharpCode.ILSpy
 		{
 			if (e.OldItems != null)
 				foreach (LoadedAssembly asm in e.OldItems)
-					history.RemoveAll(n => n.Item1.Any(nd => nd.AncestorsAndSelf().OfType<AssemblyTreeNode>().Any(a => a.LoadedAssembly == asm)));
+					history.RemoveAll(n => n.TreeNodes.Any(nd => nd.AncestorsAndSelf().OfType<AssemblyTreeNode>().Any(a => a.LoadedAssembly == asm)));
 		}
 		
 		void LoadInitialAssemblies()
@@ -510,7 +509,7 @@ namespace ICSharpCode.ILSpy
 				return;
 
 			if (recordHistory)
-				history.Record(Tuple.Create(treeView.SelectedItems.OfType<SharpTreeNode>().ToList(), decompilerTextView.GetState()));
+				history.Record(new NavigationState(treeView.SelectedItems.OfType<SharpTreeNode>(), decompilerTextView.GetState()));
 
 			if (treeView.SelectedItems.Count == 1) {
 				ILSpyTreeNode node = treeView.SelectedItem as ILSpyTreeNode;
@@ -584,22 +583,20 @@ namespace ICSharpCode.ILSpy
 
 		void NavigateHistory(bool forward)
 		{
-			var currentSelection = treeView.SelectedItems.OfType<SharpTreeNode>().ToList();
-			var state = decompilerTextView.GetState();
-			var combinedState = Tuple.Create(currentSelection, state);
+			var combinedState = new NavigationState(treeView.SelectedItems.OfType<SharpTreeNode>(), decompilerTextView.GetState());
 			history.Record(combinedState, replace: true, clearForward: false);
 			var newState = forward ? history.GoForward() : history.GoBack();
 
 			ignoreDecompilationRequests = true;
 			treeView.SelectedItems.Clear();
-			foreach (var node in newState.Item1)
+			foreach (var node in newState.TreeNodes)
 			{
 				treeView.SelectedItems.Add(node);
 			}
-			if (newState.Item1.Count > 0)
-				treeView.FocusNode(newState.Item1[0]);
+			if (newState.TreeNodes.Any())
+				treeView.FocusNode(newState.TreeNodes.First());
 			ignoreDecompilationRequests = false;
-			DecompileSelectedNodes(newState.Item2, false);
+			DecompileSelectedNodes(newState.ViewState, false);
 		}
 
 		#endregion

ILSpy/NavigationHistory.cs

@@ -12,7 +12,7 @@ namespace ICSharpCode.ILSpy
 	/// Stores the navigation history.
 	/// </summary>
 	internal sealed class NavigationHistory<T>
-		where T : class
+		where T : class, IEquatable<T>
 	{
 		private const double NavigationSecondsBeforeNewEntry = 0.5;
 
@@ -68,6 +68,8 @@ namespace ICSharpCode.ILSpy
 				if (current != null)
 					back.Add(current);
 
+				// We only store a record once, and ensure it is on the top of the stack, so we just remove the old record
+				back.Remove(node);
 				current = node;
 			}
 

ILSpy/NavigationState.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using ICSharpCode.ILSpy.TextView;
+using ICSharpCode.TreeView;
+namespace ICSharpCode.ILSpy
+{
+	public class NavigationState : IEquatable<NavigationState>
+	{
+		private HashSet<SharpTreeNode> treeNodes;
+
+		public IEnumerable<SharpTreeNode> TreeNodes { get { return treeNodes; } }
+		public DecompilerTextViewState ViewState { get; private set; }
+
+		public NavigationState(IEnumerable<SharpTreeNode> treeNodes, DecompilerTextViewState viewState)
+		{
+			this.treeNodes = new HashSet<SharpTreeNode>(treeNodes);
+			ViewState = viewState;
+		}
+
+		public bool Equals(NavigationState other)
+		{
+			// TODO: should this care about the view state as well?
+			return this.treeNodes.SetEquals(other.treeNodes);
+		}
+	}
+}