Walkthrough: Display statement completion

Article
11/04/2016

Applies to: Visual Studio Visual Studio for Mac

Note

This article applies to Visual Studio 2017. 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

You can implement language-based statement completion by defining the identifiers for which you want to provide completion and then triggering a completion session. You can define statement completion in the context of a language service, define your own file name extension and content type and then display completion for just that type. Or, you can trigger completion for an existing content type—for example, "plaintext". This walkthrough shows how to trigger statement completion for the "plaintext" content type, which is the content type of text files. The "text" content type is the ancestor of all other content types, including code and XML files.

Statement completion is typically triggered by typing certain characters—for example, by typing the beginning of an identifier such as "using". It's typically dismissed by pressing the Spacebar, Tab, or Enter key to commit a selection. You can implement the IntelliSense features that trigger when typing a character by using a command handler for the keystrokes (the IOleCommandTarget interface) and a handler provider that implements the IVsTextViewCreationListener interface. To create the completion source, which is the list of identifiers that participate in completion, implement the ICompletionSource interface and a completion source provider (the ICompletionSourceProvider interface). The providers are Managed Extensibility Framework (MEF) component parts. They're responsible for exporting the source and controller classes and importing services and brokers—for example, the ITextStructureNavigatorSelectorService, which enables navigation in the text buffer, and the ICompletionBroker, which triggers the completion session.

This walkthrough shows how to implement statement completion for a hard-coded set of identifiers. In full implementations, the language service and the language documentation are responsible for providing that content.

Prerequisites

Starting in Visual Studio 2015, you don't install the Visual Studio SDK from the download center. It's included as an optional feature in Visual Studio setup. You can also install the VS SDK later on. For more information, see Install the Visual Studio SDK.

Create 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 CompletionTest.
Add an Editor Classifier item template to the project. For more information, see Create an extension with an editor item template.
Delete the existing class files.
Add the following references to the project and make sure that CopyLocal is set to false:

Microsoft.VisualStudio.Editor

Microsoft.VisualStudio.Language.Intellisense

Microsoft.VisualStudio.OLE.Interop

Microsoft.VisualStudio.Shell.15.0

Microsoft.VisualStudio.Shell.Immutable.10.0

Microsoft.VisualStudio.TextManager.Interop

Implement the completion source

The completion source is responsible for collecting the set of identifiers and adding the content to the completion window when a user types a completion trigger, such as the first letters of an identifier. In this example, the identifiers and their descriptions are hard-coded in the AugmentCompletionSession method. In most real-world uses, you would use your language's parser to get the tokens to populate the completion list.

To implement the completion source

Add a class file and name it TestCompletionSource.

Add these imports:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel.Composition;
using Microsoft.VisualStudio.Language.Intellisense;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Operations;
using Microsoft.VisualStudio.Utilities;

Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Text
Imports System.ComponentModel.Composition
Imports Microsoft.VisualStudio.Language.Intellisense
Imports Microsoft.VisualStudio.Text
Imports Microsoft.VisualStudio.Text.Operations
Imports Microsoft.VisualStudio.Utilities

Modify the class declaration for TestCompletionSource so that it implements ICompletionSource:

internal class TestCompletionSource : ICompletionSource

Friend Class TestCompletionSource
    Implements ICompletionSource

Add private fields for the source provider, the text buffer, and a list of Completion objects (which correspond to the identifiers that will participate in the completion session):

private TestCompletionSourceProvider m_sourceProvider;
private ITextBuffer m_textBuffer;
private List<Completion> m_compList;

Private m_sourceProvider As TestCompletionSourceProvider
Private m_textBuffer As ITextBuffer
Private m_compList As List(Of Completion)

Add a constructor that sets the source provider and buffer. The TestCompletionSourceProvider class is defined in later steps:

public TestCompletionSource(TestCompletionSourceProvider sourceProvider, ITextBuffer textBuffer)
{
    m_sourceProvider = sourceProvider;
    m_textBuffer = textBuffer;
}

Public Sub New(ByVal sourceProvider As TestCompletionSourceProvider, ByVal textBuffer As ITextBuffer)
    m_sourceProvider = sourceProvider
    m_textBuffer = textBuffer
End Sub

Implement the AugmentCompletionSession method by adding a completion set that contains the completions you want to provide in the context. Each completion set contains a set of Completion completions, and corresponds to a tab of the completion window. (In Visual Basic projects, the completion window tabs are named Common and All.) The FindTokenSpanAtPosition method is defined in the next step.

void ICompletionSource.AugmentCompletionSession(ICompletionSession session, IList<CompletionSet> completionSets)
{
    List<string> strList = new List<string>();
    strList.Add("addition");
    strList.Add("adaptation");
    strList.Add("subtraction");
    strList.Add("summation");
    m_compList = new List<Completion>();
    foreach (string str in strList)
        m_compList.Add(new Completion(str, str, str, null, null));

    completionSets.Add(new CompletionSet(
        "Tokens",    //the non-localized title of the tab
        "Tokens",    //the display title of the tab
        FindTokenSpanAtPosition(session.GetTriggerPoint(m_textBuffer),
            session),
        m_compList,
        null));
}

Private Sub AugmentCompletionSession(ByVal session As ICompletionSession, ByVal completionSets As IList(Of CompletionSet)) Implements ICompletionSource.AugmentCompletionSession
    Dim strList As New List(Of String)()
    strList.Add("addition")
    strList.Add("adaptation")
    strList.Add("subtraction")
    strList.Add("summation")

    m_compList = New List(Of Completion)()
    For Each str As String In strList
        m_compList.Add(New Completion(str, str, str, Nothing, Nothing))
    Next str

    completionSets.Add(New CompletionSet(
        "Tokens",
        "Tokens",
        FindTokenSpanAtPosition(session.GetTriggerPoint(m_textBuffer),
            session),
        m_compList,
        Nothing))
End Sub

The following method is used to find the current word from the position of the cursor:

private ITrackingSpan FindTokenSpanAtPosition(ITrackingPoint point, ICompletionSession session)
{
    SnapshotPoint currentPoint = (session.TextView.Caret.Position.BufferPosition) - 1;
    ITextStructureNavigator navigator = m_sourceProvider.NavigatorService.GetTextStructureNavigator(m_textBuffer);
    TextExtent extent = navigator.GetExtentOfWord(currentPoint);
    return currentPoint.Snapshot.CreateTrackingSpan(extent.Span, SpanTrackingMode.EdgeInclusive);
}

Private Function FindTokenSpanAtPosition(ByVal point As ITrackingPoint, ByVal session As ICompletionSession) As ITrackingSpan
    Dim currentPoint As SnapshotPoint = (session.TextView.Caret.Position.BufferPosition) - 1
    Dim navigator As ITextStructureNavigator = m_sourceProvider.NavigatorService.GetTextStructureNavigator(m_textBuffer)
    Dim extent As TextExtent = navigator.GetExtentOfWord(currentPoint)
    Return currentPoint.Snapshot.CreateTrackingSpan(extent.Span, SpanTrackingMode.EdgeInclusive)
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

Implement the completion source provider

The completion source provider is the MEF component part that instantiates the completion source.

To implement the completion source provider

Add a class named TestCompletionSourceProvider that implements ICompletionSourceProvider. Export this class with a ContentTypeAttribute of "plaintext" and a NameAttribute of "test completion".

[Export(typeof(ICompletionSourceProvider))]
[ContentType("plaintext")]
[Name("token completion")]
internal class TestCompletionSourceProvider : ICompletionSourceProvider

<Export(GetType(ICompletionSourceProvider)), ContentType("plaintext"), Name("token completion")>
Friend Class TestCompletionSourceProvider
    Implements ICompletionSourceProvider

Import a ITextStructureNavigatorSelectorService, which finds the current word in the completion source.

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

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

Implement the TryCreateCompletionSource method to instantiate the completion source.

public ICompletionSource TryCreateCompletionSource(ITextBuffer textBuffer)
{
    return new TestCompletionSource(this, textBuffer);
}

Public Function TryCreateCompletionSource(ByVal textBuffer As ITextBuffer) As ICompletionSource Implements ICompletionSourceProvider.TryCreateCompletionSource
    Return New TestCompletionSource(Me, textBuffer)
End Function

Implement the completion command handler provider

The completion command handler provider is derived from a IVsTextViewCreationListener, which listens for a text view creation event and converts the view from an IVsTextView—which enables the addition of the command to the command chain of the Visual Studio shell—to an ITextView. Because this class is a MEF export, you can also use it to import the services that are required by the command handler itself.

To implement the completion command handler provider

Add a file named TestCompletionCommandHandler.

Add these using directives:

using System;
using System.ComponentModel.Composition;
using System.Runtime.InteropServices;
using Microsoft.VisualStudio;
using Microsoft.VisualStudio.Editor;
using Microsoft.VisualStudio.Language.Intellisense;
using Microsoft.VisualStudio.OLE.Interop;
using Microsoft.VisualStudio.Shell;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Editor;
using Microsoft.VisualStudio.TextManager.Interop;
using Microsoft.VisualStudio.Utilities;

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

Add a class named TestCompletionHandlerProvider that implements IVsTextViewCreationListener. Export this class with a NameAttribute of "token completion handler", a ContentTypeAttribute of "plaintext", and a TextViewRoleAttribute of Editable.

[Export(typeof(IVsTextViewCreationListener))]
[Name("token completion handler")]
[ContentType("plaintext")]
[TextViewRole(PredefinedTextViewRoles.Editable)]
internal class TestCompletionHandlerProvider : IVsTextViewCreationListener

<Export(GetType(IVsTextViewCreationListener))>
<Name("token completion handler")>
<ContentType("plaintext")> <TextViewRole(PredefinedTextViewRoles.Editable)>
Friend Class TestCompletionHandlerProvider
    Implements IVsTextViewCreationListener

Import the IVsEditorAdaptersFactoryService, which enables conversion from a IVsTextView to a ITextView, a ICompletionBroker, and a SVsServiceProvider that enables access to standard Visual Studio services.

[Import]
internal IVsEditorAdaptersFactoryService AdapterService = null;
[Import]
internal ICompletionBroker CompletionBroker { get; set; }
[Import]
internal SVsServiceProvider ServiceProvider { get; set; }

<Import()>
Friend AdapterService As IVsEditorAdaptersFactoryService = Nothing
<Import()>
Friend Property CompletionBroker() As ICompletionBroker
<Import()>
Friend Property ServiceProvider() As SVsServiceProvider

Implement the VsTextViewCreated method to instantiate the command handler.

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

    Func<TestCompletionCommandHandler> createCommandHandler = delegate() { return new TestCompletionCommandHandler(textViewAdapter, textView, this); };
    textView.Properties.GetOrCreateSingletonProperty(createCommandHandler);
}

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

    Dim createCommandHandler As Func(Of TestCompletionCommandHandler) = Function() New TestCompletionCommandHandler(textViewAdapter, textView, Me)
    textView.Properties.GetOrCreateSingletonProperty(createCommandHandler)
End Sub

Implement the completion command handler

Because statement completion is triggered by keystrokes, you must implement the IOleCommandTarget interface to receive and process the keystrokes that trigger, commit, and dismiss the completion session.

To implement the completion command handler

Add a class named TestCompletionCommandHandler that implements IOleCommandTarget:

internal class TestCompletionCommandHandler : IOleCommandTarget

Friend Class TestCompletionCommandHandler
    Implements IOleCommandTarget

Add private fields for the next command handler (to which you pass the command), the text view, the command handler provider (which enables access to various services), and a completion session:

private IOleCommandTarget m_nextCommandHandler;
private ITextView m_textView;
private TestCompletionHandlerProvider m_provider;
private ICompletionSession m_session;

Private m_nextCommandHandler As IOleCommandTarget
Private m_textView As ITextView
Private m_provider As TestCompletionHandlerProvider
Private m_session As ICompletionSession

Add a constructor that sets the text view and the provider fields, and adds the command to the command chain:

internal TestCompletionCommandHandler(IVsTextView textViewAdapter, ITextView textView, TestCompletionHandlerProvider provider)
{
    this.m_textView = textView;
    this.m_provider = provider;

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

Friend Sub New(ByVal textViewAdapter As IVsTextView, ByVal textView As ITextView, ByVal provider As TestCompletionHandlerProvider)
    Me.m_textView = textView
    Me.m_provider = provider

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

Implement the QueryStatus method by passing the command along:

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

Implement the Exec method. When this method receives a keystroke, it must do one of these things:

Allow the character to be written to the buffer, and then trigger or filter completion. (Printing characters do this.)
Commit the completion, but do not allow the character to be written to the buffer. (Whitespace, Tab, and Enter do this when a completion session is displayed.)

Allow the command to be passed on to the next handler. (All other commands.)

Because this method may display UI, call IsInAutomationFunction to make sure that it's not called in an automation context:

public int Exec(ref Guid pguidCmdGroup, uint nCmdID, uint nCmdexecopt, IntPtr pvaIn, IntPtr pvaOut)
{
    if (VsShellUtilities.IsInAutomationFunction(m_provider.ServiceProvider))
    {
        return m_nextCommandHandler.Exec(ref pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut);
    }
    //make a copy of this so we can look at it after forwarding some commands
    uint commandID = nCmdID;
    char typedChar = char.MinValue;
    //make sure the input is a char before getting it
    if (pguidCmdGroup == VSConstants.VSStd2K && nCmdID == (uint)VSConstants.VSStd2KCmdID.TYPECHAR)
    {
        typedChar = (char)(ushort)Marshal.GetObjectForNativeVariant(pvaIn);
    }

    //check for a commit character
    if (nCmdID == (uint)VSConstants.VSStd2KCmdID.RETURN
        || nCmdID == (uint)VSConstants.VSStd2KCmdID.TAB
        || (char.IsWhiteSpace(typedChar) || char.IsPunctuation(typedChar)))
    {
        //check for a selection
        if (m_session != null && !m_session.IsDismissed)
        {
            //if the selection is fully selected, commit the current session
            if (m_session.SelectedCompletionSet.SelectionStatus.IsSelected)
            {
                m_session.Commit();
                //also, don't add the character to the buffer
                return VSConstants.S_OK;
            }
            else
            {
                //if there is no selection, dismiss the session
                m_session.Dismiss();
            }
        }
    }

    //pass along the command so the char is added to the buffer
    int retVal = m_nextCommandHandler.Exec(ref pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut);
    bool handled = false;
    if (!typedChar.Equals(char.MinValue) && char.IsLetterOrDigit(typedChar))
    {
        if (m_session == null || m_session.IsDismissed) // If there is no active session, bring up completion
        {
            this.TriggerCompletion();
            m_session.Filter();
        }
        else    //the completion session is already active, so just filter
        {
            m_session.Filter();
        }
        handled = true;
    }
    else if (commandID == (uint)VSConstants.VSStd2KCmdID.BACKSPACE   //redo the filter if there is a deletion
        || commandID == (uint)VSConstants.VSStd2KCmdID.DELETE)
    {
        if (m_session != null && !m_session.IsDismissed)
            m_session.Filter();
        handled = true;
    }
    if (handled) return VSConstants.S_OK;
    return retVal;
}

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
    If VsShellUtilities.IsInAutomationFunction(m_provider.ServiceProvider) Then
        Return m_nextCommandHandler.Exec(pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut)
    End If
    'make a copy of this so we can look at it after forwarding some commands
    Dim commandID As UInteger = nCmdID
    Dim typedChar As Char = Char.MinValue
    'make sure the input is a char before getting it
    If pguidCmdGroup = VSConstants.VSStd2K AndAlso nCmdID = CUInt(VSConstants.VSStd2KCmdID.TYPECHAR) Then
        typedChar = CChar(ChrW(CUShort(Marshal.GetObjectForNativeVariant(pvaIn))))
    End If

    'check for a commit character
    If nCmdID = CUInt(VSConstants.VSStd2KCmdID.RETURN) OrElse nCmdID = CUInt(VSConstants.VSStd2KCmdID.TAB) OrElse (Char.IsWhiteSpace(typedChar) OrElse Char.IsPunctuation(typedChar)) Then
        'check for a selection
        If m_session IsNot Nothing AndAlso (Not m_session.IsDismissed) Then
            'if the selection is fully selected, commit the current session
            If m_session.SelectedCompletionSet.SelectionStatus.IsSelected Then
                m_session.Commit()
                'also, don't add the character to the buffer
                Return VSConstants.S_OK
            Else
                'if there is no selection, dismiss the session
                m_session.Dismiss()
            End If
        End If
    End If

    'pass along the command so the char is added to the buffer
    Dim retVal As Integer = m_nextCommandHandler.Exec(pguidCmdGroup, nCmdID, nCmdexecopt, pvaIn, pvaOut)
    Dim handled As Boolean = False
    If (Not typedChar.Equals(Char.MinValue)) AndAlso Char.IsLetterOrDigit(typedChar) Then
        If m_session Is Nothing OrElse m_session.IsDismissed Then ' If there is no active session, bring up completion
            Me.TriggerCompletion()
            m_session.Filter()
        Else 'the completion session is already active, so just filter
            m_session.Filter()
        End If
        handled = True
    ElseIf commandID = CUInt(VSConstants.VSStd2KCmdID.BACKSPACE) OrElse commandID = CUInt(VSConstants.VSStd2KCmdID.DELETE) Then 'redo the filter if there is a deletion
        If m_session IsNot Nothing AndAlso (Not m_session.IsDismissed) Then
            m_session.Filter()
        End If
        handled = True
    End If
    If handled Then
        Return VSConstants.S_OK
    End If
    Return retVal
End Function

This code is a private method that triggers the completion session:

private bool TriggerCompletion()
{
    //the caret must be in a non-projection location 
    SnapshotPoint? caretPoint =
    m_textView.Caret.Position.Point.GetPoint(
    textBuffer => (!textBuffer.ContentType.IsOfType("projection")), PositionAffinity.Predecessor);
    if (!caretPoint.HasValue)
    {
        return false;
    }

    m_session = m_provider.CompletionBroker.CreateCompletionSession
 (m_textView,
        caretPoint.Value.Snapshot.CreateTrackingPoint(caretPoint.Value.Position, PointTrackingMode.Positive),
        true);

    //subscribe to the Dismissed event on the session 
    m_session.Dismissed += this.OnSessionDismissed;
    m_session.Start();

    return true;
}

Private Function TriggerCompletion() As Boolean
    'the caret must be in a non-projection location 
    Dim caretPoint As SnapshotPoint? = m_textView.Caret.Position.Point.GetPoint(Function(textBuffer) ((Not textBuffer.ContentType.IsOfType("projection"))), PositionAffinity.Predecessor)
    If Not caretPoint.HasValue Then
        Return False
    End If

    m_session = m_provider.CompletionBroker.CreateCompletionSession(m_textView, caretPoint.Value.Snapshot.CreateTrackingPoint(caretPoint.Value.Position, PointTrackingMode.Positive), True)

    'subscribe to the Dismissed event on the session 
    AddHandler m_session.Dismissed, AddressOf OnSessionDismissed
    m_session.Start()

    Return True
End Function

The next example is a private method that unsubscribes from the Dismissed event:

private void OnSessionDismissed(object sender, EventArgs e)
{
    m_session.Dismissed -= this.OnSessionDismissed;
    m_session = null;
}

Private Sub OnSessionDismissed(ByVal sender As Object, ByVal e As EventArgs)
    RemoveHandler m_session.Dismissed, AddressOf OnSessionDismissed
    m_session = Nothing
End Sub

Build and test the code

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

To build and test the CompletionTest solution

Build the solution.
When you run this project in the debugger, a second instance of Visual Studio is started.
Create a text file and type some text that includes the word "add".
As you type first "a" and then "d", a list that contains "addition" and "adaptation" should appear. Notice that addition is selected. When you type another "d", the list should contain only "addition", which is now selected. You can commit "addition" by pressing the Spacebar, Tab, or Enter key, or dismiss the list by typing Esc or any other key.

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