Walkthrough: Displaying Signature Help

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11/15/2016

Note

This article applies to Visual Studio 2015. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here

Signature Help (also known as Parameter Info) displays the signature of a method in a tooltip when a user types the parameter list start character (typically an opening parenthesis). As a parameter and parameter separator (typically a comma) are typed, the tooltip is updated to show the next parameter in bold. You can define Signature Help in the context of a language service, or you can define your own file name extension and content type and display Signature Help for just that type, or you can display Signature Help for an existing content type (for example, "text"). This walkthrough shows how to display Signature Help for the "text" content type.

Signature Help is typically triggered by typing a specific character, for example, "(" (opening parenthesis), and dismissed by typing another character, for example, ")" (closing parenthesis). IntelliSense features that are triggered by typing a character can be implemented by using a command handler for the keystrokes (the IOleCommandTarget interface) and a handler provider that implements the IVsTextViewCreationListener interface. To create the Signature Help source, which is the list of signatures that participate in Signature Help, implement the ISignatureHelpSource interface and a source provider that implements the ISignatureHelpSourceProvider interface. The providers are Managed Extensibility Framework (MEF) component parts, and are responsible for exporting the source and controller classes and importing services and brokers, for example, the ITextStructureNavigatorSelectorService, which lets you navigate in the text buffer, and the ISignatureHelpBroker, which triggers the Signature Help session.

This walkthrough shows how to implement Signature Help for a hard-coded set of identifiers. In full implementations, the language is responsible for providing that content.

Prerequisites

Starting in Visual Studio 2015, you do not install the Visual Studio SDK from the download center. It is included as an optional feature in Visual Studio setup. You can also install the VS SDK later on. For more information, see Installing the Visual Studio SDK.

Creating a MEF Project

To create a MEF project

Create a C# VSIX project. (In the New Project dialog, select Visual C# / Extensibility, then VSIX Project.) Name the solution SignatureHelpTest.
Add an Editor Classifier item template to the project. For more information, see Creating an Extension with an Editor Item Template.
Delete the existing class files.
Add the following references to the project, and make sure CopyLocal is set to false:

Microsoft.VisualStudio.Editor

Microsoft.VisualStudio.Language.Intellisense

Microsoft.VisualStudio.OLE.Interop

Microsoft.VisualStudio.Shell.14.0

Microsoft.VisualStudio.TextManager.Interop

Implementing Signature Help Signatures and Parameters

The Signature Help source is based on signatures that implement ISignature, each of which contains parameters that implement IParameter. In a full implementation, this information would be obtained from the language documentation, but in this example, the signatures are hard-coded.

To implement the Signature Help signatures and parameters

Add a class file and name it SignatureHelpSource.

Add the following imports.

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel.Composition;
using System.Runtime.InteropServices;
using Microsoft.VisualStudio.Language.Intellisense;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Editor;
using Microsoft.VisualStudio.Utilities;
using Microsoft.VisualStudio.Editor;
using Microsoft.VisualStudio.Text.Operations;
using Microsoft.VisualStudio;
using Microsoft.VisualStudio.TextManager.Interop;
using Microsoft.VisualStudio.OLE.Interop;

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Text
Imports System.Collections.ObjectModel
Imports System.ComponentModel.Composition
Imports System.Runtime.InteropServices
Imports Microsoft.VisualStudio.Language.Intellisense
Imports Microsoft.VisualStudio.Text
Imports Microsoft.VisualStudio.Text.Editor
Imports Microsoft.VisualStudio.Utilities
Imports Microsoft.VisualStudio.Editor
Imports Microsoft.VisualStudio.Text.Operations
Imports Microsoft.VisualStudio
Imports Microsoft.VisualStudio.TextManager.Interop
Imports Microsoft.VisualStudio.OLE.Interop

Add a class named TestParameter that implements IParameter.

internal class TestParameter : IParameter

Friend Class TestParameter
    Implements IParameter

Add a constructor that sets all the properties.

public TestParameter(string documentation, Span locus, string name, ISignature signature)
{
    Documentation = documentation;
    Locus = locus;
    Name = name;
    Signature = signature;
}

Public Sub New(ByVal documentation As String, ByVal locus As Span, ByVal name As String, ByVal signature As ISignature)
    Me.privateDocumentation = documentation
    Me.privateLocus = locus
    Me.privateName = name
    Me.privateSignature = signature
End Sub

Add the properties of IParameter.

public string Documentation { get; private set; }
public Span Locus { get; private set; }
public string Name { get; private set; }
public ISignature Signature { get; private set; }
public Span PrettyPrintedLocus { get; private set; }

Private privateDocumentation As String
ReadOnly Property Documentation() As String Implements IParameter.Documentation
    Get
        Return privateDocumentation
    End Get

End Property
Private privateLocus As Span
ReadOnly Property Locus() As Span Implements IParameter.Locus
    Get
        Return privateLocus
    End Get
End Property
Private privateName As String
ReadOnly Property Name() As String Implements IParameter.Name
    Get
        Return privateName
    End Get
End Property
Private privateSignature As ISignature
ReadOnly Property Signature() As ISignature Implements IParameter.Signature
    Get
        Return privateSignature
    End Get
End Property
Private privatePrettyPrintedLocus As Span
ReadOnly Property PrettyPrintedLocus() As Span Implements IParameter.PrettyPrintedLocus
    Get
        Return privatePrettyPrintedLocus
    End Get
End Property

Add a class named TestSignature that implements ISignature.

internal class TestSignature : ISignature

Friend Class TestSignature
    Implements ISignature

Add some private fields.

private ITextBuffer m_subjectBuffer;
private IParameter m_currentParameter;
private string m_content;
private string m_documentation;
private ITrackingSpan m_applicableToSpan;
private ReadOnlyCollection<IParameter> m_parameters;
private string m_printContent;

Private m_subjectBuffer As ITextBuffer
Private m_currentParameter As IParameter
Private m_content As String
Private m_documentation As String
Friend m_applicableToSpan As ITrackingSpan
Friend m_parameters As ReadOnlyCollection(Of IParameter)
Private m_printContent As String

Add a constructor that sets the fields and subscribes to the Changed event.

internal TestSignature(ITextBuffer subjectBuffer, string content, string doc, ReadOnlyCollection<IParameter> parameters)
{
    m_subjectBuffer = subjectBuffer;
    m_content = content;
    m_documentation = doc;
    m_parameters = parameters;
    m_subjectBuffer.Changed += new EventHandler<TextContentChangedEventArgs>(OnSubjectBufferChanged);
}

Friend Sub New(ByVal subjectBuffer As ITextBuffer, ByVal content As String, ByVal doc As String, ByVal parameters As ReadOnlyCollection(Of IParameter))
    m_subjectBuffer = subjectBuffer
    m_content = content
    m_documentation = doc
    m_parameters = parameters
    AddHandler m_subjectBuffer.Changed, AddressOf OnSubjectBufferChanged
End Sub

Declare a CurrentParameterChanged event. This event is raised when the user fills in one of the parameters in the signature.

public event EventHandler<CurrentParameterChangedEventArgs> CurrentParameterChanged;

Public Event CurrentParameterChanged As EventHandler(Of CurrentParameterChangedEventArgs) Implements ISignature.CurrentParameterChanged

Implement the CurrentParameter property so that it raises the CurrentParameterChanged event when the property value is changed.

public IParameter CurrentParameter
{
    get { return m_currentParameter; }
    internal set
    {
        if (m_currentParameter != value)
        {
            IParameter prevCurrentParameter = m_currentParameter;
            m_currentParameter = value;
            this.RaiseCurrentParameterChanged(prevCurrentParameter, m_currentParameter);
        }
    }
}

ReadOnly Property CurrentParameter() As IParameter Implements ISignature.CurrentParameter
    Get
        Return m_currentParameter
    End Get
End Property

Add a method that raises the CurrentParameterChanged event.

private void RaiseCurrentParameterChanged(IParameter prevCurrentParameter, IParameter newCurrentParameter)
{
    EventHandler<CurrentParameterChangedEventArgs> tempHandler = this.CurrentParameterChanged;
    if (tempHandler != null)
    {
        tempHandler(this, new CurrentParameterChangedEventArgs(prevCurrentParameter, newCurrentParameter));
    }
}

Private Sub RaiseCurrentParameterChanged(ByVal prevCurrentParameter As IParameter, ByVal newCurrentParameter As IParameter)
    Dim tempHandler As EventHandler(Of CurrentParameterChangedEventArgs) = Me.CurrentParameterChangedEvent
    If tempHandler IsNot Nothing Then
        tempHandler(Me, New CurrentParameterChangedEventArgs(prevCurrentParameter, newCurrentParameter))
    End If
End Sub

Add a method that computes the current parameter by comparing the number of commas in the ApplicableToSpan to the number of commas in the signature.

internal void ComputeCurrentParameter()
{
    if (Parameters.Count == 0)
    {
        this.CurrentParameter = null;
        return;
    }

    //the number of commas in the string is the index of the current parameter
    string sigText = ApplicableToSpan.GetText(m_subjectBuffer.CurrentSnapshot);

    int currentIndex = 0;
    int commaCount = 0;
    while (currentIndex < sigText.Length)
    {
        int commaIndex = sigText.IndexOf(',', currentIndex);
        if (commaIndex == -1)
        {
            break;
        }
        commaCount++;
        currentIndex = commaIndex + 1;
    }

    if (commaCount < Parameters.Count)
    {
        this.CurrentParameter = Parameters[commaCount];
    }
    else
    {
        //too many commas, so use the last parameter as the current one.
        this.CurrentParameter = Parameters[Parameters.Count - 1];
    }
}

Friend Sub ComputeCurrentParameter()
    If Parameters.Count = 0 Then
        Me.m_currentParameter = Nothing
        Return
    End If

    'the number of commas in the string is the index of the current parameter
    Dim sigText As String = ApplicableToSpan.GetText(m_subjectBuffer.CurrentSnapshot)

    Dim currentIndex As Integer = 0
    Dim commaCount As Integer = 0
    Do While currentIndex < sigText.Length
        Dim commaIndex As Integer = sigText.IndexOf(","c, currentIndex)
        If commaIndex = -1 Then
            Exit Do
        End If
        commaCount += 1
        currentIndex = commaIndex + 1
    Loop

    If commaCount < Parameters.Count Then
        Me.m_currentParameter = Parameters(commaCount)
    Else
        'too many commas, so use the last parameter as the current one.
        Me.m_currentParameter = Parameters(Parameters.Count - 1)
    End If
End Sub

Add an event handler for the Changed event that calls the ComputeCurrentParameter() method.

internal void OnSubjectBufferChanged(object sender, TextContentChangedEventArgs e)
{
    this.ComputeCurrentParameter();
}

Friend Sub OnSubjectBufferChanged(ByVal sender As Object, ByVal e As TextContentChangedEventArgs)
    Me.ComputeCurrentParameter()
End Sub

Implement the ApplicableToSpan property. This property holds an ITrackingSpan that corresponds to the span of text in the buffer to which the signature applies.

public ITrackingSpan ApplicableToSpan
{
    get { return (m_applicableToSpan); }
    internal set { m_applicableToSpan = value; }
}

ReadOnly Property ApplicableToSpan() As ITrackingSpan Implements ISignature.ApplicableToSpan
    Get
        Return (m_applicableToSpan)
    End Get
End Property

Implement the other parameters.

public string Content
{
    get { return (m_content); }
    internal set { m_content = value; }
}

public string Documentation
{
    get { return (m_documentation); }
    internal set { m_documentation = value; }
}

public ReadOnlyCollection<IParameter> Parameters
{
    get { return (m_parameters); }
    internal set { m_parameters = value; }
}

public string PrettyPrintedContent
{
    get { return (m_printContent); }
    internal set { m_printContent = value; }
}

ReadOnly Property Content() As String Implements ISignature.Content
    Get
        Return (m_content)
    End Get
End Property

ReadOnly Property Documentation() As String Implements ISignature.Documentation
    Get
        Return (m_documentation)
    End Get
End Property

ReadOnly Property Parameters() As ReadOnlyCollection(Of IParameter) Implements ISignature.Parameters
    Get
        Return (m_parameters)
    End Get
End Property

ReadOnly Property PrettyPrintedContent() As String Implements ISignature.PrettyPrintedContent
    Get
        Return (m_printContent)
    End Get
End Property

Implementing the Signature Help Source

The Signature Help source is the set of signatures for which you provide information.

To implement the Signature Help source

Add a class named TestSignatureHelpSource that implements ISignatureHelpSource.

internal class TestSignatureHelpSource : ISignatureHelpSource

Friend Class TestSignatureHelpSource
    Implements ISignatureHelpSource

Add a reference to the text buffer.

private ITextBuffer m_textBuffer;

Private m_textBuffer As ITextBuffer

Add a constructor that sets the text buffer and the Signature Help source provider.

public TestSignatureHelpSource(ITextBuffer textBuffer)
{
    m_textBuffer = textBuffer;
}

Public Sub New(ByVal textBuffer As ITextBuffer)
    m_textBuffer = textBuffer
End Sub

Implement the AugmentSignatureHelpSession method. In this example, the signatures are hard-coded, but in a full implementation you would get this information from the language documentation.

public void AugmentSignatureHelpSession(ISignatureHelpSession session, IList<ISignature> signatures)
{
    ITextSnapshot snapshot = m_textBuffer.CurrentSnapshot;
    int position = session.GetTriggerPoint(m_textBuffer).GetPosition(snapshot);

    ITrackingSpan applicableToSpan = m_textBuffer.CurrentSnapshot.CreateTrackingSpan(
     new Span(position, 0), SpanTrackingMode.EdgeInclusive, 0);

    signatures.Add(CreateSignature(m_textBuffer, "add(int firstInt, int secondInt)", "Documentation for adding integers.", applicableToSpan));
    signatures.Add(CreateSignature(m_textBuffer, "add(double firstDouble, double secondDouble)", "Documentation for adding doubles.", applicableToSpan));

}

Public Sub AugmentSignatureHelpSession(ByVal session As ISignatureHelpSession, ByVal signatures As IList(Of ISignature)) Implements ISignatureHelpSource.AugmentSignatureHelpSession
    Dim snapshot As ITextSnapshot = m_textBuffer.CurrentSnapshot
    Dim position As Integer = session.GetTriggerPoint(m_textBuffer).GetPosition(snapshot)

    Dim applicableToSpan As ITrackingSpan = m_textBuffer.CurrentSnapshot.CreateTrackingSpan(New Span(position, 0), SpanTrackingMode.EdgeInclusive, 0)

    signatures.Add(CreateSignature(m_textBuffer, "add(int firstInt, int secondInt)", "Documentation for adding integers.", applicableToSpan))
    signatures.Add(CreateSignature(m_textBuffer, "add(double firstDouble, double secondDouble)", "Documentation for adding doubles.", applicableToSpan))
End Sub

The helper method CreateSignature() is provided just for illustration.

private TestSignature CreateSignature(ITextBuffer textBuffer, string methodSig, string methodDoc, ITrackingSpan span)
{
    TestSignature sig = new TestSignature(textBuffer, methodSig, methodDoc, null);
    textBuffer.Changed += new EventHandler<TextContentChangedEventArgs>(sig.OnSubjectBufferChanged);

    //find the parameters in the method signature (expect methodname(one, two)
    string[] pars = methodSig.Split(new char[] { '(', ',', ')' });
    List<IParameter> paramList = new List<IParameter>();

    int locusSearchStart = 0;
    for (int i = 1; i < pars.Length; i++)
    {
        string param = pars[i].Trim();

        if (string.IsNullOrEmpty(param))
            continue;

        //find where this parameter is located in the method signature
        int locusStart = methodSig.IndexOf(param, locusSearchStart);
        if (locusStart >= 0)
        {
            Span locus = new Span(locusStart, param.Length);
            locusSearchStart = locusStart + param.Length;
            paramList.Add(new TestParameter("Documentation for the parameter.", locus, param, sig));
        }
    }

    sig.Parameters = new ReadOnlyCollection<IParameter>(paramList);
    sig.ApplicableToSpan = span;
    sig.ComputeCurrentParameter();
    return sig;
}

Private Function CreateSignature(ByVal textBuffer As ITextBuffer, ByVal methodSig As String, ByVal methodDoc As String, ByVal span As ITrackingSpan) As TestSignature
    Dim sig As New TestSignature(textBuffer, methodSig, methodDoc, Nothing)
    AddHandler textBuffer.Changed, AddressOf sig.OnSubjectBufferChanged

    'find the parameters in the method signature (expect methodname(one, two)
    Dim pars() As String = methodSig.Split(New Char() {"("c, ","c, ")"c})
    Dim paramList As New List(Of IParameter)()

    Dim locusSearchStart As Integer = 0
    For i As Integer = 1 To pars.Length - 1
        Dim param As String = pars(i).Trim()

        If String.IsNullOrEmpty(param) Then
            Continue For
        End If

        'find where this parameter is located in the method signature
        Dim locusStart As Integer = methodSig.IndexOf(param, locusSearchStart)
        If locusStart >= 0 Then
            Dim locus As New Span(locusStart, param.Length)
            locusSearchStart = locusStart + param.Length
            paramList.Add(New TestParameter("Documentation for the parameter.", locus, param, sig))
        End If
    Next i

    sig.m_Parameters = New ReadOnlyCollection(Of IParameter)(paramList)
    sig.m_ApplicableToSpan = span
    sig.ComputeCurrentParameter()
    Return sig
End Function

Implement the GetBestMatch method. In this example, there are just two signatures, each of which has two parameters. Therefore, this method is not required. In a fuller implementation, in which more than one Signature Help source is available, this method is used to decide whether the highest-priority Signature Help source can supply a matching signature. If it cannot, the method returns null and the next-highest-priority source is asked to supply a match.

public ISignature GetBestMatch(ISignatureHelpSession session)
{
    if (session.Signatures.Count > 0)
    {
        ITrackingSpan applicableToSpan = session.Signatures[0].ApplicableToSpan;
        string text = applicableToSpan.GetText(applicableToSpan.TextBuffer.CurrentSnapshot);

        if (text.Trim().Equals("add"))  //get only "add" 
            return session.Signatures[0];
    }
    return null;
}

Public Function GetBestMatch(ByVal session As ISignatureHelpSession) As ISignature Implements ISignatureHelpSource.GetBestMatch
    If session.Signatures.Count > 0 Then
        Dim applicableToSpan As ITrackingSpan = session.Signatures(0).ApplicableToSpan
        Dim text As String = applicableToSpan.GetText(applicableToSpan.TextBuffer.CurrentSnapshot)

        If text.Trim().Equals("add") Then 'get only "add"
            Return session.Signatures(0)
        End If
    End If
    Return Nothing
End Function

Implement the Dispose() method:

private bool m_isDisposed;
public void Dispose()
{
    if (!m_isDisposed)
    {
        GC.SuppressFinalize(this);
        m_isDisposed = true;
    }
}

Private m_isDisposed As Boolean

Public Sub Dispose() Implements IDisposable.Dispose
    If Not m_isDisposed Then
        GC.SuppressFinalize(Me)
        m_isDisposed = True
    End If
End Sub

Implementing the Signature Help Source Provider

The Signature Help source provider is responsible for exporting the Managed Extensibility Framework (MEF) component part and for instantiating the Signature Help source.

To implement the Signature Help source provider

Add a class named TestSignatureHelpSourceProvider that implements ISignatureHelpSourceProvider, and export it with a NameAttribute, a ContentTypeAttribute of "text", and an OrderAttribute of Before="default".

[Export(typeof(ISignatureHelpSourceProvider))]
[Name("Signature Help source")]
[Order(Before = "default")]
[ContentType("text")]
internal class TestSignatureHelpSourceProvider : ISignatureHelpSourceProvider

<Export(GetType(ISignatureHelpSourceProvider)), Name("Signature Help source"), Order(Before:="default"), ContentType("text")>
Friend Class TestSignatureHelpSourceProvider
    Implements ISignatureHelpSourceProvider

Implement TryCreateSignatureHelpSource by instantiating the TestSignatureHelpSource.

public ISignatureHelpSource TryCreateSignatureHelpSource(ITextBuffer textBuffer)
{
    return new TestSignatureHelpSource(textBuffer);
}

Public Function TryCreateSignatureHelpSource(ByVal textBuffer As ITextBuffer) As ISignatureHelpSource Implements ISignatureHelpSourceProvider.TryCreateSignatureHelpSource
    Return New TestSignatureHelpSource(textBuffer)
End Function

Implementing the Command Handler

Signature Help is typically triggered by a ( character and dismissed by a ) character. You can handle these keystrokes by implementing a IOleCommandTarget so that it triggers a Signature Help session when it receives a ( character preceded by a known method name, and dismisses the session when it receives a ) character.

To implement the command handler

Add a class named TestSignatureHelpCommand that implements IOleCommandTarget.

internal sealed class TestSignatureHelpCommandHandler : IOleCommandTarget

Friend NotInheritable Class TestSignatureHelpCommandHandler
    Implements IOleCommandTarget

Add private fields for the IVsTextView adapter (which lets you add the command handler to the chain of command handlers), the text view, the Signature Help broker and session, a ITextStructureNavigator, and the next IOleCommandTarget.

IOleCommandTarget m_nextCommandHandler;
ITextView m_textView;
ISignatureHelpBroker m_broker;
ISignatureHelpSession m_session;
ITextStructureNavigator m_navigator;

Private m_nextCommandHandler As IOleCommandTarget
Private m_textView As ITextView
Private m_broker As ISignatureHelpBroker
Private m_session As ISignatureHelpSession
Private m_navigator As ITextStructureNavigator

Add a constructor to initialize these fields and to add the command filter to the chain of command filters.

internal TestSignatureHelpCommandHandler(IVsTextView textViewAdapter, ITextView textView, ITextStructureNavigator nav, ISignatureHelpBroker broker)
{
    this.m_textView = textView;
    this.m_broker = broker;
    this.m_navigator = nav;

    //add this to the filter chain
    textViewAdapter.AddCommandFilter(this, out m_nextCommandHandler);
}

Friend Sub New(ByVal textViewAdapter As IVsTextView, ByVal textView As ITextView, ByVal nav As ITextStructureNavigator, ByVal broker As ISignatureHelpBroker)
    Me.m_textView = textView
    Me.m_broker = broker
    Me.m_navigator = nav

    'add this to the filter chain
    textViewAdapter.AddCommandFilter(Me, m_nextCommandHandler)
End Sub

Implement the Exec method to trigger the Signature Help session when the command filter receives a ( character after one of the known method names, and to dismiss the session when it receives a ) character while the session is still active. In every case, the command is forwarded.

public int Exec(ref Guid pguidCmdGroup, uint nCmdID, uint nCmdexecopt, IntPtr pvaIn, IntPtr pvaOut)
{
    char typedChar = char.MinValue;

    if (pguidCmdGroup == VSConstants.VSStd2K && nCmdID == (uint)VSConstants.VSStd2KCmdID.TYPECHAR)
    {
        typedChar = (char)(ushort)Marshal.GetObjectForNativeVariant(pvaIn);
        if (typedChar.Equals('('))
        {
            //move the point back so it's in the preceding word
            SnapshotPoint point = m_textView.Caret.Position.BufferPosition - 1;
            TextExtent extent = m_navigator.GetExtentOfWord(point);
            string word = extent.Span.GetText();
            if (word.Equals("add"))
                m_session = m_broker.TriggerSignatureHelp(m_textView);

        }
        else if (typedChar.Equals(')') && m_session != null)
        {
            m_session.Dismiss();
            m_session = null;
        }
    }
    return m_nextCommandHandler.Exec(ref pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut);
}

Public Function Exec(ByRef pguidCmdGroup As Guid, ByVal nCmdID As UInteger, ByVal nCmdexecopt As UInteger, ByVal pvaIn As IntPtr, ByVal pvaOut As IntPtr) As Integer Implements IOleCommandTarget.Exec
    Dim typedChar As Char = Char.MinValue

    If pguidCmdGroup = VSConstants.VSStd2K AndAlso nCmdID = CUInt(VSConstants.VSStd2KCmdID.TYPECHAR) Then
        typedChar = CChar(ChrW(CUShort(Marshal.GetObjectForNativeVariant(pvaIn))))
        If typedChar.Equals("("c) Then
            'move the point back so it's in the preceding word
            Dim point As SnapshotPoint = m_textView.Caret.Position.BufferPosition - 1
            Dim extent As TextExtent = m_navigator.GetExtentOfWord(point)
            Dim word As String = extent.Span.GetText()
            If word.Equals("add") Then
                m_session = m_broker.TriggerSignatureHelp(m_textView)
            End If

        ElseIf typedChar.Equals(")"c) AndAlso m_session IsNot Nothing Then
            m_session.Dismiss()
            m_session = Nothing
        End If
    End If
    Return m_nextCommandHandler.Exec(pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut)
End Function

Implement the QueryStatus method so that it always forwards the command.

public int QueryStatus(ref Guid pguidCmdGroup, uint cCmds, OLECMD[] prgCmds, IntPtr pCmdText)
{
    return m_nextCommandHandler.QueryStatus(ref pguidCmdGroup, cCmds, prgCmds, pCmdText);
}

Public Function QueryStatus(ByRef pguidCmdGroup As Guid, ByVal cCmds As UInteger, ByVal prgCmds() As OLECMD, ByVal pCmdText As IntPtr) As Integer Implements IOleCommandTarget.QueryStatus
    Return m_nextCommandHandler.QueryStatus(pguidCmdGroup, cCmds, prgCmds, pCmdText)
End Function

Implementing the Signature Help Command Provider

You can provide the Signature Help command by implementing the IVsTextViewCreationListener to instantiate the command handler when the text view is created.

To implement the Signature Help command provider

Add a class named TestSignatureHelpController that implements IVsTextViewCreationListener and export it with the NameAttribute, ContentTypeAttribute, and TextViewRoleAttribute.

[Export(typeof(IVsTextViewCreationListener))]
[Name("Signature Help controller")]
[TextViewRole(PredefinedTextViewRoles.Editable)]
[ContentType("text")]
internal class TestSignatureHelpCommandProvider : IVsTextViewCreationListener

<Export(GetType(IVsTextViewCreationListener)), Name("Signature Help controller"), TextViewRole(PredefinedTextViewRoles.Editable), ContentType("text")>
Friend Class TestSignatureHelpCommandProvider
    Implements IVsTextViewCreationListener

Import the IVsEditorAdaptersFactoryService (used to get the ITextView, given the IVsTextView object), the ITextStructureNavigatorSelectorService (used to find the current word), and the ISignatureHelpBroker (to trigger the Signature Help session).

[Import]
internal IVsEditorAdaptersFactoryService AdapterService;

[Import]
internal ITextStructureNavigatorSelectorService NavigatorService { get; set; }

[Import]
internal ISignatureHelpBroker SignatureHelpBroker;

<Import()>
Friend AdapterService As IVsEditorAdaptersFactoryService

<Import()>
Friend Property NavigatorService() As ITextStructureNavigatorSelectorService

<Import()>
Friend SignatureHelpBroker As ISignatureHelpBroker

Implement the VsTextViewCreated method by instantiating the TestSignatureCommandHandler.

public void VsTextViewCreated(IVsTextView textViewAdapter)
{
    ITextView textView = AdapterService.GetWpfTextView(textViewAdapter);
    if (textView == null)
        return;

    textView.Properties.GetOrCreateSingletonProperty(
         () => new TestSignatureHelpCommandHandler(textViewAdapter,
            textView,
            NavigatorService.GetTextStructureNavigator(textView.TextBuffer),
            SignatureHelpBroker));
}

Public Sub VsTextViewCreated(ByVal textViewAdapter As IVsTextView) Implements IVsTextViewCreationListener.VsTextViewCreated
    Dim textView As ITextView = AdapterService.GetWpfTextView(textViewAdapter)
    If textView Is Nothing Then
        Return
    End If

    textView.Properties.GetOrCreateSingletonProperty(Function() New TestSignatureHelpCommandHandler(textViewAdapter, textView, NavigatorService.GetTextStructureNavigator(textView.TextBuffer), SignatureHelpBroker))
End Sub

Building and Testing the Code

To test this code, build the SignatureHelpTest solution and run it in the experimental instance.

To build and test the SignatureHelpTest solution

Build the solution.
When you run this project in the debugger, a second instance of Visual Studio is instantiated.
Create a text file and type some text that includes the word "add" plus an opening parenthesis.
After you type the opening parenthesis, you should see a tooltip that displays a list of the two signatures for the add() method.

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