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Walkthrough: Implementing Code Snippets

 

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The latest version of this topic can be found at Walkthrough: Implementing Code Snippets.

You can create code snippets and include them in an editor extension so that users of the extension can add them to their own code.

A code snippet is a fragment of code or other text that can be incorporated in a file. To view all snippets that have been registered for particular programming languages, on the Tools menu, click Code Snippet Manager. To insert a snippet in a file, right-click where you want the snippet, click Insert Snippet or Surround With, locate the snippet you want, and then double-click it. Press TAB or SHIFT+TAB to modify the relevant parts of the snippet and then press ENTER or ESC to accept it. For more information, see Code Snippets.

A code snippet is contained in an XML file that has the .snippet file name extension. A snippet can contain fields that are highlighted after the snippet is inserted so that the user can find and change them. A snippet file also provides information for the Code Snippet Manager so that it can display the snippet name in the correct category. For information about the snippet schema, see Code Snippets Schema Reference.

This walkthrough teaches how to accomplish these tasks:

  1. Create and register code snippets for a specific language.

  2. Add the Insert Snippet command to a shortcut menu.

  3. Implement snippet expansion.

This walkthrough is based on Walkthrough: Displaying Statement Completion.

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.

Typically, code snippets are associated with a registered language service. However, you do not have to implement a LanguageService to register code snippets. Instead, just specify a GUID in the snippet index file and then use the same GUID in the ProvideLanguageCodeExpansionAttribute that you add to your project.

The following steps demonstrate how to create code snippets and associate them with a specific GUID.

  1. Create the following directory structure:

    %InstallDir%\TestSnippets\Snippets\1033\

    where %InstallDir% is the Visual Studio installation folder. (Although this path is typically used to install code snippets, you can specify any path.)

  2. In the \1033\ folder, create an .xml file and name it TestSnippets.xml. (Although this name is typically used for a snippet index file, you can specify any name as long as it has an .xml file name extension.) Add the following text, and then delete the placeholder GUID and add your own.

    <?xml version="1.0" encoding="utf-8" ?>  
    <SnippetCollection>  
        <Language Lang="TestSnippets" Guid="{00000000-0000-0000-0000-000000000000}">  
            <SnippetDir>  
                <OnOff>On</OnOff>  
                <Installed>true</Installed>  
                <Locale>1033</Locale>  
                <DirPath>%InstallRoot%\TestSnippets\Snippets\%LCID%\</DirPath>  
                <LocalizedName>Snippets</LocalizedName>  
            </SnippetDir>  
        </Language>  
    </SnippetCollection>  
    
    
  3. Create a file in the snippet folder, name it test.snippet, and then add the following text:

    <?xml version="1.0" encoding="utf-8" ?>  
    <CodeSnippets  xmlns="http://schemas.microsoft.com/VisualStudio/2005/CodeSnippet">  
        <CodeSnippet Format="1.0.0">  
            <Header>  
                <Title>Test replacement fields</Title>  
                <Shortcut>test</Shortcut>  
                <Description>Code snippet for testing replacement fields</Description>  
                <Author>MSIT</Author>  
                <SnippetTypes>  
                    <SnippetType>Expansion</SnippetType>  
                </SnippetTypes>  
            </Header>  
            <Snippet>  
                <Declarations>  
                    <Literal>  
                      <ID>param1</ID>  
                        <ToolTip>First field</ToolTip>  
                        <Default>first</Default>  
                    </Literal>  
                    <Literal>  
                        <ID>param2</ID>  
                        <ToolTip>Second field</ToolTip>  
                        <Default>second</Default>  
                    </Literal>  
                </Declarations>  
                <References>  
                   <Reference>  
                       <Assembly>System.Windows.Forms.dll</Assembly>  
                   </Reference>  
                </References>  
                <Code Language="TestSnippets">  
                    <![CDATA[MessageBox.Show("$param1$");  
         MessageBox.Show("$param2$");]]>  
                </Code>    
            </Snippet>  
        </CodeSnippet>  
    </CodeSnippets>  
    
    

The following steps show how to register the code snippets.

To register code snippets for a specific GUID

  1. Open the CompletionTest project. For information about how to create this project, see Walkthrough: Displaying Statement Completion.

  2. In the project, add references to the following assemblies:

    • Microsoft.VisualStudio.TextManager.Interop

    • Microsoft.VisualStudio.TextManager.Interop.8.0

    • microsoft.msxml

  3. In the project, open the source.extension.vsixmanifest file.

  4. Make sure that the Assets tab contains a VsPackage content type and that Project is set to the name of the project.

  5. Select the CompletionTest project and in the Properties window set Generate Pkgdef File to true. Save the project.

  6. Add a static SnippetUtilities class to the project.

    Module SnippetUtilities
    

  7. In the SnippetUtilities class, define a GUID and give it the value that you used in the SnippetsIndex.xml file.

        Friend Const LanguageServiceGuidStr As String = "00000000-0000-0000-0000-00000000"
    

  8. Add the ProvideLanguageCodeExpansionAttribute to the TestCompletionHandler class. This attribute can be added to any public or internal (non-static) class in the project. (You may have to add a using statement for the Microsoft.VisualStudio.Shell namespace.)

        <ProvideLanguageCodeExpansion(
        SnippetUtilities.LanguageServiceGuidStr,
        "TestSnippets",
        0,
        "TestSnippets",
        "%InstallRoot%\TestSnippets\Snippets\%LCID%\SnippetsIndex.xml",
        SearchPaths:="%InstallRoot%\TestSnippets\Snippets\%LCID%\",
        ForceCreateDirs:="%InstallRoot%\TestSnippets\Snippets\%LCID%\")>
        Friend Class TestCompletionCommandHandler
            Implements IOleCommandTarget
    

  9. Build and run the project. In the experimental instance of Visual Studio that starts when the project is run, the snippet you just registered should be displayed in the Code Snippets Manager under the TestSnippets language.

The Insert Snippet command is not included on the shortcut menu for a text file. Therefore, you must enable the command.

To add the Insert Snippet command to the shortcut menu

  1. Open the TestCompletionCommandHandler class file.

    Because this class implements IOleCommandTarget, you can activate the Insert Snippet command in the QueryStatus method. Before you enable the command, check that this method is not being called inside an automation function because when the Insert Snippet command is clicked, it will display the snippet picker user interface (UI).

            Public Function QueryStatus(ByRef pguidCmdGroup As Guid, ByVal cCmds As UInteger, ByVal prgCmds As OLECMD(), ByVal pCmdText As IntPtr) As Integer Implements IOleCommandTarget.QueryStatus
                If Not VsShellUtilities.IsInAutomationFunction(m_provider.ServiceProvider) Then
                    If pguidCmdGroup = VSConstants.VSStd2K AndAlso cCmds > 0 Then
                        ' make the Insert Snippet command appear on the context menu 
                        If CUInt(prgCmds(0).cmdID) = CUInt(VSConstants.VSStd2KCmdID.INSERTSNIPPET) Then
                            prgCmds(0).cmdf = CInt(Constants.MSOCMDF_ENABLED) Or CInt(Constants.MSOCMDF_SUPPORTED)
                            Return VSConstants.S_OK
                        End If
                    End If
                End If
    
                Return m_nextCommandHandler.QueryStatus(pguidCmdGroup, cCmds, prgCmds, pCmdText)
            End Function
    

  2. Build and run the project. In the experimental instance, open a file that has the .zzz file name extension and then right-click anywhere in it. The Insert Snippet command should appear on the shortcut menu.

This section shows how to implement code snippet expansion so that the snippet picker UI is displayed when Insert Snippet is clicked on the shortcut menu. A code snippet is also expanded when a user types the code-snippet shortcut and then presses TAB.

To display the snippet picker UI and to enable navigation and post-insertion snippet acceptance, use the M:Microsoft.VisualStudio.OLE.Interop.IOleCommandTarget.Exec(System.Guid,System.UInt32,System.UInt32,System.IntPtr,System.IntPtr) method. The insertion itself is handled by the OnItemChosen method.

The implementation of code snippet expansion uses legacy Microsoft.VisualStudio.TextManager.Interop interfaces. When you translate from the current editor classes to the legacy code, remember that the legacy interfaces use a combination of line numbers and column numbers to specify locations in a text buffer, but the current classes use one index. Therefore, if a buffer has three lines each of which has ten characters (plus a newline, which counts as 1 character), the fourth character on the third line is at position 27 in the current implementation, but it is at line 2, position 3 in the old implementation.

To implement snippet expansion

  1. To the file that contains the TestCompletionCommandHandler class, add the following using statements.

    Imports Microsoft.VisualStudio.Text.Operations
    Imports MSXML
    

  2. Make the TestCompletionCommandHandler class implement the IVsExpansionClient interface.

        <ProvideLanguageCodeExpansion(
        SnippetUtilities.LanguageServiceGuidStr,
        "TestSnippets",
        0,
        "TestSnippets",
        "%InstallRoot%\TestSnippets\Snippets\%LCID%\SnippetsIndex.xml",
        SearchPaths:="%InstallRoot%\TestSnippets\Snippets\%LCID%\",
        ForceCreateDirs:="%InstallRoot%\TestSnippets\Snippets\%LCID%\")>
        Friend Class TestCompletionCommandHandler
            Implements IOleCommandTarget
            Implements IVsExpansionClient
    

  3. In the TestCompletionCommandHandlerProvider class, import the ITextStructureNavigatorSelectorService.

        <Import()>
        Friend Property NavigatorService As ITextStructureNavigatorSelectorService
    

  4. Add some private fields for the code expansion interfaces and the IVsTextView.

            Dim m_vsTextView As IVsTextView
            Dim m_exManager As IVsExpansionManager
            Dim m_exSession As IVsExpansionSession
    

  5. In the constructor of the TestCompletionCommandHandler class, set the following fields.

            Friend Sub New(ByVal textViewAdapter As IVsTextView, ByVal textView As ITextView, ByVal provider As TestCompletionHandlerProvider)
                Me.m_textView = textView
                Me.m_provider = provider
                Me.m_vsTextView = textViewAdapter
    
                Dim textManager As IVsTextManager2 = DirectCast(m_provider.ServiceProvider.GetService(GetType(SVsTextManager)), IVsTextManager2)
                textManager.GetExpansionManager(m_exManager)
                m_exSession = Nothing
    
                'add the command to the command chain
                textViewAdapter.AddCommandFilter(Me, m_nextCommandHandler)
            End Sub
    

  6. To display the snippet picker when the user clicks the Insert Snippet command, add the following code to the Exec method. (To make this explanation more readable, the Exec() code that is used for statement completion is not shown; instead, blocks of code are added to the existing method.) Add the following block of code after the code that checks for a character.

                'code previously written for Exec
                If pguidCmdGroup = VSConstants.VSStd2K AndAlso nCmdID = CUInt(VSConstants.VSStd2KCmdID.TYPECHAR) Then
                    typedChar = ChrW(CUShort(Marshal.GetObjectForNativeVariant(pvaIn)))
                End If
                'the snippet picker code starts here
                If nCmdID = CUInt(VSConstants.VSStd2KCmdID.INSERTSNIPPET) Then
                    Dim textManager As IVsTextManager2 = DirectCast(m_provider.ServiceProvider.GetService(GetType(SVsTextManager)), IVsTextManager2)
    
                    textManager.GetExpansionManager(m_exManager)
                    m_exManager.InvokeInsertionUI(
                        m_vsTextView,
                        Me,
                        New Guid(SnippetUtilities.LanguageServiceGuidStr),
                        Nothing,
                        0,
                        0,
                        Nothing,
                        0,
                        0,
                        "TestSnippets",
                        String.Empty)
                    Return VSConstants.S_OK
                End If
    

  7. If a snippet has fields that can be navigated, the expansion session is kept open until the expansion is explicitly accepted; if the snippet has no fields, the session is closed and is returned as null by the InvokeInsertionUI method. In the Exec method, after the snippet picker UI code that you added in the previous step, add the following code to handle snippet navigation (when the user presses TAB or SHIFT+TAB after snippet insertion).

                'the expansion insertion is handled in OnItemChosen
                'if the expansion session is still active, handle tab/backtab/return/cancel
                If m_exSession IsNot Nothing Then
                    If nCmdID = CUInt(VSConstants.VSStd2KCmdID.BACKTAB) Then
                        m_exSession.GoToPreviousExpansionField()
                        Return VSConstants.S_OK
                    ElseIf nCmdID = CUInt(VSConstants.VSStd2KCmdID.TAB) Then
                        m_exSession.GoToNextExpansionField(0)
                        'false to support cycling through all the fields
                        Return VSConstants.S_OK
                    ElseIf nCmdID = CUInt(VSConstants.VSStd2KCmdID.[RETURN]) OrElse nCmdID = CUInt(VSConstants.VSStd2KCmdID.CANCEL) Then
                        If m_exSession.EndCurrentExpansion(0) = VSConstants.S_OK Then
                            m_exSession = Nothing
                            Return VSConstants.S_OK
                        End If
                    End If
                End If
    

  8. To insert the code snippet when the user types the corresponding shortcut and then presses TAB, add code to the Exec method. The private method that inserts the snippet will be shown in a later step. Add the following code after the navigation code that you added in the previous step.

                'neither an expansion session nor a completion session is open, but we got a tab, so check whether the last word typed is a snippet shortcut 
                If m_session Is Nothing AndAlso m_exSession Is Nothing AndAlso nCmdID = CUInt(VSConstants.VSStd2KCmdID.TAB) Then
                    'get the word that was just added 
                    Dim pos As CaretPosition = m_textView.Caret.Position
                    Dim word As TextExtent = m_provider.NavigatorService.GetTextStructureNavigator(m_textView.TextBuffer).GetExtentOfWord(pos.BufferPosition - 1)
                    Dim textString As String = word.Span.GetText()
                    'if it is a code snippet, insert it, otherwise carry on
                    If InsertAnyExpansion(textString, Nothing, Nothing) Then
                        Return VSConstants.S_OK
                    End If
                End If
    

  9. Implement the methods of the IVsExpansionClient interface. In this implementation, the only methods of interest are EndExpansion and OnItemChosen. The other methods should just return S_OK.

            Public Function EndExpansion() As Integer Implements IVsExpansionClient.EndExpansion
                m_exSession = Nothing
                Return VSConstants.S_OK
            End Function
    
            Public Function FormatSpan(ByVal pBuffer As IVsTextLines, ByVal ts As TextSpan()) As Integer Implements IVsExpansionClient.FormatSpan
                Return VSConstants.S_OK
            End Function
    
            Public Function GetExpansionFunction(ByVal xmlFunctionNode As IXMLDOMNode, ByVal bstrFieldName As String, ByRef pFunc As IVsExpansionFunction) As Integer Implements IVsExpansionClient.GetExpansionFunction
                pFunc = Nothing
                Return VSConstants.S_OK
            End Function
    
            Public Function IsValidKind(ByVal pBuffer As IVsTextLines, ByVal ts As TextSpan(), ByVal bstrKind As String, ByRef pfIsValidKind As Integer) As Integer Implements IVsExpansionClient.IsValidKind
                pfIsValidKind = 1
                Return VSConstants.S_OK
            End Function
    
            Public Function IsValidType(ByVal pBuffer As IVsTextLines, ByVal ts() As TextSpan, ByVal rgTypes() As String, ByVal iCountTypes As Integer, ByRef pfIsValidType As Integer) As Integer Implements IVsExpansionClient.IsValidType
                pfIsValidType = 1
                Return VSConstants.S_OK
            End Function
    
            Public Function OnAfterInsertion(ByVal pSession As IVsExpansionSession) As Integer Implements IVsExpansionClient.OnAfterInsertion
                Return VSConstants.S_OK
            End Function
    
            Public Function OnBeforeInsertion(ByVal pSession As IVsExpansionSession) As Integer Implements IVsExpansionClient.OnBeforeInsertion
                Return VSConstants.S_OK
            End Function
    
            Public Function PositionCaretForEditing(ByVal pBuffer As IVsTextLines, ByVal ts As TextSpan()) As Integer Implements IVsExpansionClient.PositionCaretForEditing
                Return VSConstants.S_OK
            End Function
    

  10. Implement the OnItemChosen method. The helper method that actually inserts the expansions will be covered in a later step. The TextSpan provides line and column information, which you can get from the IVsTextView.

            Public Function OnItemChosen(ByVal pszTitle As String, ByVal pszPath As String) As Integer Implements IVsExpansionClient.OnItemChosen
                InsertAnyExpansion(Nothing, pszTitle, pszPath)
                Return VSConstants.S_OK
            End Function
    

  11. The following private method inserts a code snippet, based either on the shortcut or on the title and path. It then calls the InsertNamedExpansion method with the snippet.

            Private Function InsertAnyExpansion(ByVal shortcut As String, ByVal title As String, ByVal path As String) As Boolean
                Dim endColumn As Integer, startLine As Integer
                'get the column number from  the IVsTextView, not the ITextView
                m_vsTextView.GetCaretPos(startLine, endColumn)
    
                Dim addSpan As New TextSpan()
                addSpan.iStartIndex = endColumn
                addSpan.iEndIndex = endColumn
                addSpan.iStartLine = startLine
                addSpan.iEndLine = startLine
    
                'get the expansion from the shortcut
                If shortcut IsNot Nothing Then
                    'reset the TextSpan to the width of the shortcut, because we're going to replace the shortcut with the expansion
                    addSpan.iStartIndex = addSpan.iEndIndex - shortcut.Length
    
                    m_exManager.GetExpansionByShortcut(
                        Me,
                        New Guid(SnippetUtilities.LanguageServiceGuidStr),
                        shortcut,
                        m_vsTextView,
                        New TextSpan() {addSpan},
                        0,
                        path,
                        title)
                End If
                If title IsNot Nothing AndAlso path IsNot Nothing Then
                    Dim textLines As IVsTextLines = Nothing
                    m_vsTextView.GetBuffer(textLines)
                    Dim bufferExpansion As IVsExpansion = DirectCast(textLines, IVsExpansion)
    
                    If bufferExpansion IsNot Nothing Then
                        Dim hr As Integer = bufferExpansion.InsertNamedExpansion(
                            title,
                            path,
                            addSpan,
                            Me,
                            New Guid(SnippetUtilities.LanguageServiceGuidStr),
                            0,
                            m_exSession)
                        If VSConstants.S_OK = hr Then
                            Return True
                        End If
                    End If
                End If
                Return False
            End Function
    

You can test whether snippet expansion works in your project.

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

  2. Open a text file and type some text.

  3. Right-click somewhere in the text and then click Insert Snippet.

  4. The snippet picker UI should appear with a pop-up that says Test replacement fields. Double-click the pop-up.

    The following snippet should be inserted.

    MessageBox.Show("first");  
    MessageBox.Show("second");  
    
    

    Do not press ENTER or ESC.

  5. Press TAB and SHIFT+TAB to toggle between "first" and "second".

  6. Accept the insertion by pressing either ENTER or ESC.

  7. In a different part of the text, type "test" and then press TAB. Because "test" is the code-snippet shortcut, the snippet should be inserted again.

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