diff --git a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterDialog.xaml b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterDialog.xaml
index 10385f9702713d3bc54bd4ade39d67c2920dca49..89bed49d14ad952e4302d9b416af7263613ae1a0 100644
--- a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterDialog.xaml
+++ b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterDialog.xaml
@@ -42,15 +42,15 @@
             <Label Grid.Row="0" Grid.Column="0" Content="{Binding ElementName=dialog, Path=TypeNameLabel}" />
             <Border Grid.Row="0" Grid.Column="1" BorderThickness="1" Margin="6,0,0,0">
                <ContentControl x:Name="TypeNameContentControl" Focusable="True" PreviewKeyDown="TypeNameContentControl_PreviewKeyDown" Margin="100,0,100,15" BorderBrush="{DynamicResource {x:Static SystemColors.InactiveBorderBrushKey}}" />
            </Border>
             <Label Grid.Row="1" Grid.Column="0" Content="{Binding ElementName=dialog, Path=ParameterNameLabel}" />
-            <TextBox Grid.Row="1" Grid.Column="1" Width="200" Text="{Binding ParameterName}" Margin="100,0,100,15" />
+            <TextBox Grid.Row="1" Grid.Column="1" Width="200" Text="{Binding ParameterName, Mode=TwoWay}" Margin="100,0,100,15" TextChanged="TextBox_ParameterNameChanged" />
             <Label Grid.Row="2" Grid.Column="0" Content="{Binding ElementName=dialog, Path=CallsiteValueLabel}" />
-            <TextBox Grid.Row="2" Grid.Column="1" Width="200" Text="{Binding CallsiteValue}" Margin="100,0,100,15" />
+            <TextBox Grid.Row="2" Grid.Column="1" Width="200" Text="{Binding CallsiteValue, Mode=TwoWay}" Margin="100,0,100,15" />
         </Grid>
         <StackPanel Grid.Row="1" 
                     HorizontalAlignment="Right" 
                     Margin="0, 11, 0, 0"
                     Orientation="Horizontal" Width="153">
-            <vs:DialogButton x:Uid="OKButton" 
+            <vs:DialogButton x:Uid="OKButton" x:Name="OKButton"
                     Content="{Binding ElementName=dialog, Path=OK}" 
                     Margin="0, 0, 0, 0" 
                     Padding="{StaticResource ResourceKey=okCancelButtonPadding}"
diff --git a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterDialog.xaml.cs b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterDialog.xaml.cs
index f39fef07a9818d517b59c5e9acf0ca8b32b597dd..766e8961f9e9444a35990b79d5c86c248623bdfd 100644
--- a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterDialog.xaml.cs
+++ b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterDialog.xaml.cs
@@ -14,9 +14,18 @@ namespace Microsoft.VisualStudio.LanguageServices.Implementation.ChangeSignature
     internal partial class AddParameterDialog : DialogWindow
     {
         public readonly AddParameterDialogViewModel ViewModel;
-        private readonly IVsTextLines _vsTextLines;
-        private readonly IVsTextView _textView;
-        private readonly IWpfTextView _wpfTextView;
+        private readonly IntellisenseTextBoxViewModel _intellisenseTextBoxView;
+        private bool _isValid;
+
+        private bool IsValid
+        {
+            get { return _isValid; }
+            set
+            {
+                this.OKButton.IsEnabled = value;
+                _isValid = value;
+            }
+        }
 
         public string OK { get { return ServicesVSResources.OK; } }
         public string Cancel { get { return ServicesVSResources.Cancel; } }
@@ -29,16 +38,16 @@ internal partial class AddParameterDialog : DialogWindow
 
         public string AddParameterDialogTitle { get { return ServicesVSResources.Add_Parameter; } }
 
-        public AddParameterDialog(
-            IVsTextLines vsTextLines,
-            IVsTextView vsTextView,
-            IWpfTextView wpfTextView)
+        public AddParameterDialog(IntellisenseTextBoxViewModel intellisenseTextBoxViewModel)
         {
+            // TODO this should be initlialized when called for Edit.
             ViewModel = new AddParameterDialogViewModel();
-            _vsTextLines = vsTextLines;
-            _textView = vsTextView;
-            _wpfTextView = wpfTextView;
+            _intellisenseTextBoxView = intellisenseTextBoxViewModel;
             this.Loaded += AddParameterDialog_Loaded;
+            DataContext = ViewModel;
+
+            // This is for Add. For edit, it should be true by default.
+            IsValid = false;
 
             InitializeComponent();
         }
@@ -46,7 +55,7 @@ internal partial class AddParameterDialog : DialogWindow
         private void AddParameterDialog_Loaded(object sender, RoutedEventArgs e)
         {
             IntellisenseTextBox typeNameTextBox = new IntellisenseTextBox(
-                _vsTextLines, _textView, _wpfTextView, TypeNameContentControl);
+                _intellisenseTextBoxView, TypeNameContentControl);
             this.TypeNameContentControl.Content = typeNameTextBox;
         }
 
@@ -54,7 +63,6 @@ private void OK_Click(object sender, RoutedEventArgs e)
         {
             if (ViewModel.TrySubmit())
             {
-                // TODO maybe we should try binding.
                 ViewModel.TypeName = ((IntellisenseTextBox)TypeNameContentControl.Content).Text;
                 DialogResult = true;
             }
@@ -83,7 +91,6 @@ private void TypeNameContentControl_PreviewKeyDown(object sender, KeyEventArgs e
                     {
                         // Do nothing. This case is handled in parent control KeyDown events.
                     }
-
                     else if (e.Key == Key.Tab && !typeNameTextBox.HasActiveIntellisenseSession)
                     {
                         // Do nothing. This case is handled in parent control KeyDown events.
@@ -96,5 +103,15 @@ private void TypeNameContentControl_PreviewKeyDown(object sender, KeyEventArgs e
                 }
             }
         }
+
+        private void TextBox_ParameterNameChanged(object sender, System.Windows.Controls.TextChangedEventArgs e)
+        {
+            // check for empty
+            // check for starting with non-letter
+            // check for special symbols
+            // check for matching other parameter names
+            // if not valid and _isValid, then _isValid = false;
+            // if valid and !_isValid, then validate all controls
+        }
     }
 }
diff --git a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterTextViewModelProvider.cs b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterTextViewModelProvider.cs
index 16eedeab21ad584c40a956bff2b58cb9cdc9ae33..da1d0917f959c0f48aed540e7f8dad62ddcfa0dc 100644
--- a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterTextViewModelProvider.cs
+++ b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/AddParameterTextViewModelProvider.cs
@@ -27,11 +27,11 @@ public ITextViewModel CreateTextViewModel(ITextDataModel dataModel, ITextViewRol
             var span = projectionSnapshot.GetSourceSpans()[1];
             var mappedSpans = projectionSnapshot.MapFromSourceSnapshot(span);
             var elisionBuffer =
-                ProjectionBufferFactoryService.CreateElisionBuffer(/*resolver=*/null,
-                                            new NormalizedSnapshotSpanCollection(
-                                                new[]{ new SnapshotSpan(dataModel.DocumentBuffer.CurrentSnapshot, mappedSpans[0])
-                                             }),
-                                            ElisionBufferOptions.None);
+                ProjectionBufferFactoryService.CreateElisionBuffer(
+                    projectionEditResolver: null,
+                    exposedSpans: new NormalizedSnapshotSpanCollection(
+                        new[] { new SnapshotSpan(dataModel.DocumentBuffer.CurrentSnapshot, mappedSpans[0]) }),
+                    options: ElisionBufferOptions.None);
 
             return new ElisionBufferTextViewModel(dataModel, elisionBuffer);
         }
diff --git a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/ChangeSignatureWorkspace.cs b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/ChangeSignatureWorkspace.cs
index 1146ca21f74d5ee4af712931750c38127226ab51..ec3c15d137f266a17478e023234cac836dfbcf7c 100644
--- a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/ChangeSignatureWorkspace.cs
+++ b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/ChangeSignatureWorkspace.cs
@@ -24,7 +24,8 @@ public ChangeSignatureWorkspace(Solution solution, Project project)
             Options = Options.WithChangedOption(EditorCompletionOptions.UseSuggestionMode, true);
         }
 
-        private string GetDocumentText()
+        // TODO do we need to keep this?
+        private static string GetDocumentText()
         {
             return $@"
 {{
diff --git a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/VisualStudioChangeSignatureOptionsService.cs b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/VisualStudioChangeSignatureOptionsService.cs
index 4065f21ff9a17b9250968db000899b29a0595428..0e435aa9818a0d18e2d0f8281dd4e3ab4bf9eeb3 100644
--- a/src/VisualStudio/Core/Def/Implementation/ChangeSignature/VisualStudioChangeSignatureOptionsService.cs
+++ b/src/VisualStudio/Core/Def/Implementation/ChangeSignature/VisualStudioChangeSignatureOptionsService.cs
@@ -170,14 +170,14 @@ public AddedParameterResult GetAddedParameter(Document document, int insertPosit
             // Start getting the compilation so the PartialSolution will be ready when the user starts typing in the window
             await document.Project.GetCompilationAsync(cancellationToken).ConfigureAwait(false);
 
-            var roleSet = _textEditorFactoryService.CreateTextViewRoleSet(
+            ITextViewRoleSet roleSet = _textEditorFactoryService.CreateTextViewRoleSet(
                 PredefinedTextViewRoles.Editable,
                 PredefinedTextViewRoles.Interactive,
                 AddParameterTextViewRole);
 
-            var vsTextView = _editorAdaptersFactoryService.CreateVsTextViewAdapter(_serviceProvider, roleSet);
+            IVsTextView vsTextView = _editorAdaptersFactoryService.CreateVsTextViewAdapter(_serviceProvider, roleSet);
 
-            var initView = new[] {
+            INITVIEW[] initView = new[] {
                 new INITVIEW()
                 {
                     fSelectionMargin = 0,
@@ -198,7 +198,7 @@ public AddedParameterResult GetAddedParameter(Document document, int insertPosit
             IWpfTextView wpfTextView = _editorAdaptersFactoryService.GetWpfTextView(vsTextView);
             wpfTextView.TextBuffer.ChangeContentType(_contentType, null);
 
-            return new AddParameterDialog(vsTextLines, vsTextView, wpfTextView);
+            return new AddParameterDialog(new IntellisenseTextBoxViewModel(vsTextView, wpfTextView));
         }
     }
 }
diff --git a/src/VisualStudio/Core/Def/Implementation/Utilities/IntellisenseTextBox.cs b/src/VisualStudio/Core/Def/Implementation/Utilities/IntellisenseTextBox.cs
index 56804cb9abf8b860a3056d88581b23628c265f53..32b8e8f17294644ab9bad9a0a4e26ea68d34c88d 100644
--- a/src/VisualStudio/Core/Def/Implementation/Utilities/IntellisenseTextBox.cs
+++ b/src/VisualStudio/Core/Def/Implementation/Utilities/IntellisenseTextBox.cs
@@ -27,11 +27,6 @@ namespace Microsoft.VisualStudio.LanguageServices.Implementation
     /// </summary>
     internal class IntellisenseTextBox : FrameworkElement, IOleCommandTarget
     {
-        /// <summary>
-        /// Contains the text in the buffer
-        /// </summary>
-        private readonly IVsTextLines _vsTextLines;
-
         /// <summary>
         /// IWpfTextView container
         /// </summary>
@@ -55,11 +50,9 @@ internal class IntellisenseTextBox : FrameworkElement, IOleCommandTarget
         /// <summary>
         /// Initializes a new instance of the <see cref="IntellisenseTextBox"/> class.
         /// </summary>
-        public IntellisenseTextBox(
-            IVsTextLines vsTextLines, IVsTextView vsTextView, IWpfTextView wpfTextView, ContentControl container)
+        public IntellisenseTextBox(IntellisenseTextBoxViewModel viewModel, ContentControl container)
         {
-            this._vsTextLines = vsTextLines;
-            this.InitializeEditorControl(vsTextView, wpfTextView, container);
+            this.InitializeEditorControl(viewModel, container);
         }
 
         /// <summary>
@@ -91,15 +84,7 @@ public bool HasActiveIntellisenseSession
         /// </summary>
         public string Text
         {
-            get
-            {
-                int length;
-                string text;
-                // TODO why 0?
-                this._vsTextLines.GetLengthOfLine(0, out length);
-                this._vsTextLines.GetLineText(0, 0, 0, length, out text);
-                return text;
-            }
+            get => this._textViewHost.TextView.TextSnapshot.GetText();
         }
 
         ///// <summary>
@@ -107,10 +92,7 @@ public string Text
         ///// </summary>
         protected override int VisualChildrenCount
         {
-            get
-            {
-                return 1;
-            }
+            get => 1;
         }
 
         /// <summary>
@@ -275,15 +257,12 @@ protected override void OnGotFocus(RoutedEventArgs e)
         /// <summary>
         /// Initializes the editor control
         /// </summary>
-        private void InitializeEditorControl(IVsTextView vsTextView, IWpfTextView wpfTextView, ContentControl container)
+        private void InitializeEditorControl(IntellisenseTextBoxViewModel viewModel, ContentControl container)
         {
             IComponentModel componentModel = (IComponentModel)Package.GetGlobalService(typeof(SComponentModel));
 
-            // TODO Set text buffer initial contents
-            // ErrorHandler.ThrowOnFailure(vsTextBuffer.InitializeContent(initialContent, initialContent != null ? initialContent.Length : 0));
-
             // Sets editor options that control its final look
-            IEditorOptions editorOptions = wpfTextView.Properties.GetProperty(typeof(IEditorOptions)) as IEditorOptions;
+            IEditorOptions editorOptions = viewModel.WpfTextView.Properties.GetProperty(typeof(IEditorOptions)) as IEditorOptions;
             editorOptions.SetOptionValue("TextViewHost/ZoomControl", false);
             editorOptions.SetOptionValue(DefaultWpfViewOptions.AppearanceCategory, appearanceCategory);
 
@@ -301,14 +280,14 @@ private void InitializeEditorControl(IVsTextView vsTextView, IWpfTextView wpfTex
             IEditorOperationsFactoryService editorOperationsFactoryService = componentModel.GetService<IEditorOperationsFactoryService>();
             if (editorOperationsFactoryService != null)
             {
-                this._editorOperations = editorOperationsFactoryService.GetEditorOperations(wpfTextView);
+                this._editorOperations = editorOperationsFactoryService.GetEditorOperations(viewModel.WpfTextView);
             }
 
-            ErrorHandler.ThrowOnFailure(vsTextView.AddCommandFilter(this, out this._nextCommandTarget));
+            ErrorHandler.ThrowOnFailure(viewModel.VsTextView.AddCommandFilter(this, out this._nextCommandTarget));
 
             // Get the host control to render the view
             IVsEditorAdaptersFactoryService editorAdapterFactory = componentModel.GetService<IVsEditorAdaptersFactoryService>();
-            this._textViewHost = editorAdapterFactory.GetWpfTextViewHost(vsTextView);
+            this._textViewHost = editorAdapterFactory.GetWpfTextViewHost(viewModel.VsTextView);
 
             // For non-blurry text
             TextOptions.SetTextFormattingMode(this._textViewHost.HostControl, TextFormattingMode.Display);
diff --git a/src/VisualStudio/Core/Def/Implementation/Utilities/IntellisenseTextBoxViewModel.cs b/src/VisualStudio/Core/Def/Implementation/Utilities/IntellisenseTextBoxViewModel.cs
new file mode 100644
index 0000000000000000000000000000000000000000..4addba75c96194000a7ac6847bb56cb81ff10907
--- /dev/null
+++ b/src/VisualStudio/Core/Def/Implementation/Utilities/IntellisenseTextBoxViewModel.cs
@@ -0,0 +1,18 @@
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using Microsoft.VisualStudio.Text.Editor;
+using Microsoft.VisualStudio.TextManager.Interop;
+
+namespace Microsoft.VisualStudio.LanguageServices.Implementation
+{
+    internal readonly struct IntellisenseTextBoxViewModel
+    {
+        public readonly IVsTextView VsTextView;
+        public readonly IWpfTextView WpfTextView;
+        public IntellisenseTextBoxViewModel(IVsTextView vsTextView, IWpfTextView wpfTextView)
+        {
+            VsTextView = vsTextView;
+            WpfTextView = wpfTextView;
+        }
+    }
+}