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Walkthrough: Displaying Statement Completion

You can implement language-based features such as 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, or you can define your own file name extension and content type, and display completion for just that type, or you can trigger completion for an existing content type (such as "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 is typically dismissed by pressing the SPACEBAR, TAB, or ENTER to commit a selection. 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 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, 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 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.

To complete this walkthrough, you must install the Visual Studio 2012 SDK.

Note Note

For more information about the Visual Studio SDK, see Extending Visual Studio Overview. To find out how to download the Visual Studio SDK, see Visual Studio Extensibility Developer Center on the MSDN Web site.

To create a MEF project

  1. Create an Editor Classifier project. Name the solution CompletionTest.

  2. Open the source.extension.vsixmanifest file in the VSIX Manifest Editor.

  3. Make sure that the Content heading contains a MEF Component content type and that the Path is set to CompletionTest.dll.

  4. Save and close source.extension.vsixmanifest.

  5. Add the following references to the project and make sure that CopyLocal is set to false:







  6. Delete the existing class files.

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 theAugmentCompletionSession 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

  1. Add a class file and name it TestCompletionSource.

  2. Add the following 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;
  3. Modify the class declaration for TestCompletionSource so that it implements ICompletionSource.

    internal class TestCompletionSource : ICompletionSource
  4. 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;
  5. 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;
  6. 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>();
        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
  7. The following method is used to find the current word from the position of the caret.

    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);
  8. Implement the Dispose() method:

    private bool m_isDisposed;
    public void Dispose()
        if (!m_isDisposed)
            m_isDisposed = true;

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

To implement the completion source provider

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

    [Name("token completion")]
    internal class TestCompletionSourceProvider : ICompletionSourceProvider
  2. Import a ITextStructureNavigatorSelectorService, which is to be used to find the current word in the completion source.

    internal ITextStructureNavigatorSelectorService NavigatorService { get; set; }
  3. Implement the TryCreateCompletionSource method to instantiate the completion source.

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

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 allows the command to be added to the command chain of the Visual Studio shell) to an ITextView. Since this class is a MEF export, you can also use it to import the services that will be needed by the command handler itself.

To implement the completion command handler provider

  1. Add a file named TestCompletionCommandHandler.

  2. Add the following using statements.

    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;
  3. 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.

    [Name("token completion handler")]
    internal class TestCompletionHandlerProvider : IVsTextViewCreationListener
  4. Import the IVsEditorAdaptersFactoryService, which lets you convert from a IVsTextView to a ITextView, a ICompletionBroker, and a SVsServiceProvider, which allows you to access standard Visual Studio services..

    internal IVsEditorAdaptersFactoryService AdapterService = null;
    internal ICompletionBroker CompletionBroker { get; set; }
    internal SVsServiceProvider ServiceProvider { get; set; }
  5. Implement the VsTextViewCreated method to instantiate the command handler.

    public void VsTextViewCreated(IVsTextView textViewAdapter)
        ITextView textView = AdapterService.GetWpfTextView(textViewAdapter);
        if (textView == null)
        Func<TestCompletionCommandHandler> createCommandHandler = delegate() { return new TestCompletionCommandHandler(textViewAdapter, textView, this); };

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

To implement the completion command handler

  1. Add a class named TestCompletionCommandHandler that implements IOleCommandTarget.

    internal class TestCompletionCommandHandler : IOleCommandTarget
  2. Add private fields for the next command handler (to which you pass the command), the text view, the command handler provider (which allows you to access various services), and a completion session.

    private IOleCommandTarget m_nextCommandHandler;
    private ITextView m_textView;
    private TestCompletionHandlerProvider m_provider;
    private ICompletionSession m_session;
  3. 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);
  4. 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);
  5. 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).

    Since this method may display UI, you should make sure that it is not called in an automation context by calling IsInAutomationFunction.

    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 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)
                    //also, don't add the character to the buffer 
                    return VSConstants.S_OK;
                    //if there is no selection, dismiss the session
        //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
            else     //the completion session is already active, so just 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)
            handled = true;
        if (handled) return VSConstants.S_OK;
        return retVal;
  6. The following code is a private method that triggers the completion session.

    private bool TriggerCompletion()
        //the caret must be in a non-projection location 
        SnapshotPoint? caretPoint =
        textBuffer => (!textBuffer.ContentType.IsOfType("projection")), PositionAffinity.Predecessor);
        if (!caretPoint.HasValue)
            return false;
        m_session = m_provider.CompletionBroker.CreateCompletionSession
            caretPoint.Value.Snapshot.CreateTrackingPoint(caretPoint.Value.Position, PointTrackingMode.Positive),
        //subscribe to the Dismissed event on the session 
        m_session.Dismissed += this.OnSessionDismissed;
        return true;
  7. The following code 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;

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

To build and test the CompletionTest solution

  1. Build the solution.

  2. When you run this project in the debugger, a second instance of Visual Studio is instantiated.

  3. Create a text file and type some text that includes the word "add".

  4. As you type first "a" and then "d", a list that contains "addition" and "adaptation" should be displayed. 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, or dismiss the list by typing ESC or any other character.