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Walkthrough: Creating a Custom Text Template Host

A text template host provides an environment that enables the text template transformation engine to run. The host is responsible for managing the engine's interaction with the file system. The engine or directive processor that needs a file or an assembly can request a resource from the host. The host can then search directories and the global assembly cache to locate the requested resource. For more information, see Architecture of the Text Template Transformation Process.

You can write a custom host if you want to use the text template transformation functionality from outside Visual Studio or if you want to integrate that functionality into custom tools. To create a custom host, you must create a class that inherits from ITextTemplatingEngineHost. For the documentation of the individual methods, see ITextTemplatingEngineHost.

Tasks illustrated in this walkthrough include the following:

  • Creating a custom text template host.

  • Testing the custom host.

To complete this walkthrough, you must have the following:

In this walkthrough, you create a custom host in an executable application that can be called from the command line. The application will accept a text template file as an argument, read the template, call the engine to transform the template, and display any errors that occur in the Command Prompt window.

To create a custom host

  1. In Visual Studio, create a new Visual Basic or C# console application named CustomHost.

  2. Add a reference to the Microsoft.VisualStudio.TextTemplating Assembly.

  3. Replace the code in the Program.cs or Module1.vb file with the following code.

    using System;
    using System.IO;
    using System.CodeDom.Compiler;
    using System.Collections.Generic;
    using System.Text;
    using Microsoft.VisualStudio.TextTemplating;
    
    namespace CustomHost
    {
        //The text template transformation engine is responsible for running 
        //the transformation process.
        //The host is responsible for all input and output, locating files, 
        //and anything else related to the external environment.
        //-------------------------------------------------------------------------
        class CustomCmdLineHost : ITextTemplatingEngineHost
        {
            //the path and file name of the text template that is being processed
            //---------------------------------------------------------------------
            internal string TemplateFileValue;
            public string TemplateFile
            {
                get { return TemplateFileValue; }
            }
    
    
            //This will be the extension of the generated text output file.
            //The host can provide a default by setting the value of the field here.
            //The engine can change this value based on the optional output directive
            //if the user specifies it in the text template.
            //---------------------------------------------------------------------
            private string fileExtensionValue = ".txt";
            public string FileExtension
            {
                get { return fileExtensionValue; }
            }
    
    
            //This will be the encoding of the generated text output file.
            //The host can provide a default by setting the value of the field here.
            //The engine can change this value based on the optional output directive
            //if the user specifies it in the text template.
            //---------------------------------------------------------------------
            private Encoding fileEncodingValue = Encoding.UTF8;
            public Encoding FileEncoding
            {
                get { return fileEncodingValue; }
            }
    
    
            //These are the errors that occur when the engine processes a template.
            //The engine passes the errors to the host when it is done processing,
            //and the host can decide how to display them. For example, the host 
            //can display the errors in the UI or write them to a file.
            //---------------------------------------------------------------------
            private CompilerErrorCollection errorsValue;
            public CompilerErrorCollection Errors
            {
                get { return errorsValue; }
            }
    
    
            //The host can provide standard assembly references.
            //The engine will use these references when compiling and
            //executing the generated transformation class.
            //--------------------------------------------------------------
            public IList<string> StandardAssemblyReferences
            {
                get
                {
                    return new string[]
                    {
                        //If this host searches standard paths and the GAC,
                        //we can specify the assembly name like this.
                        //---------------------------------------------------------
                        //"System"
    
                        //Because this host only resolves assemblies from the 
                        //fully qualified path and name of the assembly,
                        //this is a quick way to get the code to give us the
                        //fully qualified path and name of the System assembly.
                        //---------------------------------------------------------
                        typeof(System.Uri).Assembly.Location
                    };
                }
            }
    
    
            //The host can provide standard imports or using statements.
            //The engine will add these statements to the generated 
            //transformation class.
            //--------------------------------------------------------------
            public IList<string> StandardImports
            {
                get
                {
                    return new string[]
                    {
                        "System"
                    };
                }
            }
    
    
            //The engine calls this method based on the optional include directive
            //if the user has specified it in the text template.
            //This method can be called 0, 1, or more times.
            //---------------------------------------------------------------------
            //The included text is returned in the context parameter.
            //If the host searches the registry for the location of include files,
            //or if the host searches multiple locations by default, the host can
            //return the final path of the include file in the location parameter.
            //---------------------------------------------------------------------
            public bool LoadIncludeText(string requestFileName, out string content, out string location)
            {
                content = System.String.Empty;
                location = System.String.Empty;
           
                //If the argument is the fully qualified path of an existing file,
                //then we are done.
                //----------------------------------------------------------------
                if (File.Exists(requestFileName))
                {
                    content = File.ReadAllText(requestFileName);
                    return true;
                }
    
                //This can be customized to search specific paths for the file.
                //This can be customized to accept paths to search as command line
                //arguments.
                //----------------------------------------------------------------
                else
                {
                    return false;
                }
            }
    
    
            //Passes in the name of a service. If you have that service, you need to 
            //pass back a pointer to it. Otherwise, you need to pass back NULL to 
            //indicate that you have no knowledge of that service.
            //--------------------------------------------------------------------
            public object GetHostOption(string optionName)
            {
            object returnObject;
            switch (optionName)
            {
            case "CacheAssemblies":
                        returnObject = true;
         break;
            default:
            returnObject = null;
            break;
            }
            return returnObject;
            }
    
    
            //The engine calls this method to resolve assembly references used in
            //the generated transformation class project and for the optional 
            //assembly directive if the user has specified it in the text template.
            //This method can be called 0, 1, or more times.
            //---------------------------------------------------------------------
            public string ResolveAssemblyReference(string assemblyReference)
            {
                //If the argument is the fully qualified path of an existing file,
                //then we are done. (This does not do any work.)
                //----------------------------------------------------------------
                if (File.Exists(assemblyReference))
                {
                    return assemblyReference;
                }
    
                //Maybe the assembly is in the same folder as the text template that 
                //called the directive.
                //----------------------------------------------------------------
                string candidate = Path.Combine(Path.GetDirectoryName(this.TemplateFile), assemblyReference);
                if (File.Exists(candidate))
                {
                    return candidate;
                }
    
                //This can be customized to search specific paths for the file
                //or to search the GAC.
                //----------------------------------------------------------------
    
                //This can be customized to accept paths to search as command line
                //arguments.
                //----------------------------------------------------------------
    
                //If we cannot do better, return the original file name.
                return "";
            }
    
    
            //The engine calls this method based on the directives the user has 
            //specified in the text template.
            //This method can be called 0, 1, or more times.
            //---------------------------------------------------------------------
            public Type ResolveDirectiveProcessor(string processorName)
            {
                //This host will not resolve any specific processors.
    
                //Check the processor name, and if it is the name of a processor the 
                //host wants to support, return the type of the processor.
                //---------------------------------------------------------------------
                if (string.Compare(processorName, "XYZ", StringComparison.OrdinalIgnoreCase) == 0)
                {
                    //return typeof();
                }
    
                //This can be customized to search specific paths for the file
                //or to search the GAC
    
                //If the directive processor cannot be found, throw an error.
                throw new Exception("Directive Processor not found");
            }
    
    
            //A directive processor can call this method if a file name does not 
            //have a path.
            //The host can attempt to provide path information by searching 
            //specific paths for the file and returning the file and path if found.
            //This method can be called 0, 1, or more times.
            //---------------------------------------------------------------------
            public string ResolvePath(string fileName)
            {
                if (fileName == null)
                {
                    throw new ArgumentNullException("the file name cannot be null");
                }
    
                //If the argument is the fully qualified path of an existing file,
                //then we are done
                //----------------------------------------------------------------
                if (File.Exists(fileName))
                {
                    return fileName;
                }
    
                //Maybe the file is in the same folder as the text template that 
                //called the directive.
                //----------------------------------------------------------------
                string candidate = Path.Combine(Path.GetDirectoryName(this.TemplateFile), fileName);
                if (File.Exists(candidate))
                {
                    return candidate;
                }
    
                //Look more places.
                //----------------------------------------------------------------
                //More code can go here...
    
                //If we cannot do better, return the original file name.
                return fileName;
            }
    
    
            //If a call to a directive in a text template does not provide a value
            //for a required parameter, the directive processor can try to get it
            //from the host by calling this method.
            //This method can be called 0, 1, or more times.
            //---------------------------------------------------------------------
            public string ResolveParameterValue(string directiveId, string processorName, string parameterName)
            {
                if (directiveId == null)
                {
                    throw new ArgumentNullException("the directiveId cannot be null");
                }
                if (processorName == null)
                {
                    throw new ArgumentNullException("the processorName cannot be null");
                }
                if (parameterName == null)
                {
                    throw new ArgumentNullException("the parameterName cannot be null");
                }
    
                //Code to provide "hard-coded" parameter values goes here.
                //This code depends on the directive processors this host will interact with.
    
                //If we cannot do better, return the empty string.
                return String.Empty;
            }
    
    
            //The engine calls this method to change the extension of the 
            //generated text output file based on the optional output directive 
            //if the user specifies it in the text template.
            //---------------------------------------------------------------------
            public void SetFileExtension(string extension)
            {
                //The parameter extension has a '.' in front of it already.
                //--------------------------------------------------------
                fileExtensionValue = extension;
            }
    
    
            //The engine calls this method to change the encoding of the 
            //generated text output file based on the optional output directive 
            //if the user specifies it in the text template.
            //----------------------------------------------------------------------
            public void SetOutputEncoding(System.Text.Encoding encoding, bool fromOutputDirective)
            {
                fileEncodingValue = encoding;
            }
    
    
            //The engine calls this method when it is done processing a text
            //template to pass any errors that occurred to the host.
            //The host can decide how to display them.
            //---------------------------------------------------------------------
            public void LogErrors(CompilerErrorCollection errors)
            {
                errorsValue = errors;
            }
    
    
            //This is the application domain that is used to compile and run
            //the generated transformation class to create the generated text output.
            //----------------------------------------------------------------------
            public AppDomain ProvideTemplatingAppDomain(string content)
            {
                //This host will provide a new application domain each time the 
                //engine processes a text template.
                //-------------------------------------------------------------
                return AppDomain.CreateDomain("Generation App Domain");
    
                //This could be changed to return the current appdomain, but new 
                //assemblies are loaded into this AppDomain on a regular basis.
                //If the AppDomain lasts too long, it will grow indefintely, 
                //which might be regarded as a leak.
    
                //This could be customized to cache the application domain for 
                //a certain number of text template generations (for example, 10).
    
                //This could be customized based on the contents of the text 
                //template, which are provided as a parameter for that purpose.
            }
        }
    
    
        //This will accept the path of a text template as an argument.
        //It will create an instance of the custom host and an instance of the
        //text templating transformation engine, and will transform the
        //template to create the generated text output file.
        //-------------------------------------------------------------------------
        class Program
        {
            static void Main(string[] args)
            {
                try
                {
                    ProcessTemplate(args);
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
            }
    
            static void ProcessTemplate(string[] args)
            {
                string templateFileName = null;
    
                if (args.Length == 0)
                {
                    throw new System.Exception("you must provide a text template file path");
                }
    
                templateFileName = args[0];
    
                if (templateFileName == null)
                {
                    throw new ArgumentNullException("the file name cannot be null");
                }
    
                if (!File.Exists(templateFileName))
                {
                    throw new FileNotFoundException("the file cannot be found");
                }
    
                CustomCmdLineHost host = new CustomCmdLineHost();
                Engine engine = new Engine();
    
                host.TemplateFileValue = templateFileName;
    
                //Read the text template.
                string input = File.ReadAllText(templateFileName);
    
                //Transform the text template.
                string output = engine.ProcessTemplate(input, host);
    
                string outputFileName = Path.GetFileNameWithoutExtension(templateFileName);
                outputFileName = Path.Combine(Path.GetDirectoryName(templateFileName), outputFileName);
                outputFileName = outputFileName + "1" + host.FileExtension;
    
                File.WriteAllText(outputFileName, output, host.FileEncoding);
    
                foreach (CompilerError error in host.Errors)
                {
                    Console.WriteLine(error.ToString());
                }
            }
        }
    }
    

    Imports System
    Imports System.IO
    Imports System.CodeDom.Compiler
    Imports System.Collections.Generic
    Imports System.Text
    Imports Microsoft.VisualStudio.TextTemplating
    
    Namespace CustomHost
    
        'The text template transformation engine is responsible for running 
        'the transformation process.
        'The host is responsible for all input and output, locating files, 
        'and anything else related to the external environment.
        '-------------------------------------------------------------------------
        Public Class CustomCmdLineHost
            Implements ITextTemplatingEngineHost
    
            'the path and file name of the text template that is being processed
            '---------------------------------------------------------------------
            Friend TemplateFileValue As String
            Public ReadOnly Property TemplateFile() As String Implements ITextTemplatingEngineHost.TemplateFile
                Get
                    Return TemplateFileValue
                End Get
            End Property
    
    
            'This will be the extension of the generated text output file.
            'The host can provide a default by setting the value of the field here.
            'The engine can change this based on the optional output directive
            'if the user specifies it in the text template.
            '---------------------------------------------------------------------
            Private fileExtensionValue As String = ".txt"
            Public ReadOnly Property FileExtension() As String
                Get
                    Return fileExtensionValue
                End Get
            End Property
    
    
            'This will be the encoding of the generated text output file.
            'The host can provide a default by setting the value of the field here.
            'The engine can change this value based on the optional output directive
            'if the user specifies it in the text template.
            '---------------------------------------------------------------------
            Private fileEncodingValue As Encoding = Encoding.UTF8
            Public ReadOnly Property fileEncoding() As Encoding
                Get
                    Return fileEncodingValue
                End Get
            End Property
    
    
            'These are the errors that occur when the engine processes a template.
            'The engine passes the errors to the host when it is done processing,
            'and the host can decide how to display them. For example, the host 
            'can display the errors in the UI or write them to a file.
            '---------------------------------------------------------------------
            Private errorsValue As CompilerErrorCollection
            Public ReadOnly Property Errors() As CompilerErrorCollection
                Get
                    Return errorsValue
                End Get
            End Property
    
    
            'The host can provide standard assembly references.
            'The engine will use these references when compiling and
            'executing the generated transformation class.
            '--------------------------------------------------------------
            Public ReadOnly Property StandardAssemblyReferences() As IList(Of String) Implements ITextTemplatingEngineHost.StandardAssemblyReferences
                Get
                    'If this host searches standard paths and the GAC,
                    'we can specify the assembly name like this.
                    '---------------------------------------------------------
                    'Return New String() {"System"}
    
                    'Because this host only resolves assemblies from the 
                    'fully qualified path and name of the assembly,
                    'this is a quick way to get the code to give us the
                    'fully qualified path and name of the System assembly.
                    '---------------------------------------------------------
                    Return New String() {(New System.UriBuilder()).GetType().Assembly.Location}
                End Get
            End Property
    
    
            'The host can provide standard imports or imports statements.
            'The engine will add these statements to the generated 
            'transformation class.
            '--------------------------------------------------------------
            Public ReadOnly Property StandardImports() As IList(Of String) Implements ITextTemplatingEngineHost.StandardImports
                Get
                    Return New String() {"System"}
                End Get
            End Property
    
    
            'Passes in the name of a service. If you have that service, you need to 
            'pass back a pointer to it. Otherwise, you need to pass back NULL to 
            'indicate that you have no knowledge of that service.
            '--------------------------------------------------------------------
            Public Function GetHostOption(ByVal optionName As String) As Object Implements ITextTemplatingEngineHost.GetHostOption
                Dim returnObject As Object
                Select Case optionName
                    Case "CacheAssemblies"
                        returnObject = True
                    Case Else
                        returnObject = False
                End Select
                Return returnObject
            End Function
    
    
            'The engine calls this method based on the optional include directive
            'if the user has specified it in the text template.
            'This method can be called 0, 1, or more times.
            '---------------------------------------------------------------------
            'The included text is returned in the context parameter.
            'If the host searches the registry for the location of include files
            'or if the host searches multiple locations by default, the host can
            'return the final path of the include file in the location parameter.
            '---------------------------------------------------------------------
            Public Function LoadIncludeText(ByVal requestFileName As String, ByRef content As String, ByRef location As String) As Boolean Implements ITextTemplatingEngineHost.LoadIncludeText
    
                content = System.String.Empty
                location = System.String.Empty
    
                'If the argument is the fully qualified path of an existing file,
                'then we are done.
                '----------------------------------------------------------------
                If File.Exists(requestFileName) Then
    
                    content = File.ReadAllText(requestFileName)
                    Return True
    
                'This can be customized to search specific paths for the file.
                'This can be customized to accept paths to search as command line
                'arguments.
                '----------------------------------------------------------------
                Else
                    Return False
                End If
            End Function
    
    
    
    
    
            'The engine calls this method to resolve assembly references used in
            'the generated transformation class project and for the optional 
            'assembly directive if the user has specified it in the text template.
            'This method can be called 0, 1, or more times.
            '---------------------------------------------------------------------
            Public Function ResolveAssemblyReference(ByVal assemblyReference As String) As String Implements ITextTemplatingEngineHost.ResolveAssemblyReference
    
                'If the argument is the fully qualified path of an existing file,
                'then we are done. (This does not do any work.)
                '----------------------------------------------------------------
                If File.Exists(assemblyReference) Then
                    Return assemblyReference
                End If
    
    
                'Maybe the assembly is in the same folder as the text template that 
                'called the directive.
                '----------------------------------------------------------------
                Dim candidate As String = Path.Combine(Path.GetDirectoryName(Me.TemplateFile), assemblyReference)
                If File.Exists(candidate) Then
                    Return candidate
                End If
    
                'This can be customized to search specific paths for the file,
                'or to search the GAC.
                '----------------------------------------------------------------
    
                'This can be customized to accept paths to search as command line
                'arguments.
                '----------------------------------------------------------------
    
                'If we cannot do better, return the original file name.
                Return ""
            End Function
    
    
            'The engine calls this method based on the directives the user has 
            'specified in the text template.
            'This method can be called 0, 1, or more times.
            '---------------------------------------------------------------------
            Public Function ResolveDirectiveProcessor(ByVal processorName As String) As System.Type Implements ITextTemplatingEngineHost.ResolveDirectiveProcessor
                'This host will not resolve any specific processors.
    
                'Check the processor name, and if it is the name of a processor the 
                'host wants to support, return the type of the processor.
                '---------------------------------------------------------------------
                If String.Compare(processorName, "XYZ", StringComparison.InvariantCultureIgnoreCase) = 0 Then
                    'return typeof()
                End If
    
                'This can be customized to search specific paths for the file,
                'or to search the GAC.
    
                'If the directive processor cannot be found, throw an error.
                Throw New Exception("Directive Processor not found")
            End Function
    
    
            'A directive processor can call this method if a file name does not 
            'have a path.
            'The host can attempt to provide path information by searching 
            'specific paths for the file and returning the file and path if found.
            'This method can be called 0, 1, or more times.
            '---------------------------------------------------------------------
            Public Function ResolvePath(ByVal fileName As String) As String Implements ITextTemplatingEngineHost.ResolvePath
    
                If fileName Is Nothing Then
                    Throw New ArgumentNullException("the file name cannot be null")
                End If
    
                'If the argument is the fully qualified path of an existing file,
                'then we are done.
                '----------------------------------------------------------------
                If File.Exists(fileName) Then
                    Return fileName
                End If
    
                'Maybe the file is in the same folder as the text template that 
                'called the directive.
                '----------------------------------------------------------------
                Dim candidate As String = Path.Combine(Path.GetDirectoryName(Me.TemplateFile), fileName)
                If File.Exists(candidate) Then
                    Return candidate
                End If
    
                'Look more places.
                '----------------------------------------------------------------
                'More code can go here...
    
                'If we cannot do better, return the original file name
                Return fileName
            End Function
    
    
            'If a call to a directive in a text template does not provide a value
            'for a required parameter, the directive processor can try to get it
            'from the host by calling this method.
            'This method can be called 0, 1, or more times.
            '---------------------------------------------------------------------
            Public Function ResolveParameterValue(ByVal directiveId As String, ByVal processorName As String, ByVal parameterName As String) As String Implements ITextTemplatingEngineHost.ResolveParameterValue
    
                If directiveId Is Nothing Then
                    Throw New ArgumentNullException("the directiveId cannot be null")
                End If
                If processorName Is Nothing Then
                    Throw New ArgumentNullException("the processorName cannot be null")
                End If
                If parameterName Is Nothing Then
                    Throw New ArgumentNullException("the parameterName cannot be null")
                End If
    
                'Code to provide "hard-coded" parameter values goes here.
                'This code depends on the directive processors this host will interact with.
    
                'If we cannot do better, return the empty string.
                Return String.Empty
            End Function
    
    
            'The engine calls this method to change the extension of the 
            'generated text output file based on the optional output directive 
            'if the user specifies it in the text template.
            '---------------------------------------------------------------------
            Public Sub SetFileExtension(ByVal extension As String) Implements ITextTemplatingEngineHost.SetFileExtension
    
                'The parameter extension has a '.' in front of it already.
                '--------------------------------------------------------
                fileExtensionValue = extension
            End Sub
    
    
            'The engine calls this method to change the encoding of the 
            'generated text output file based on the optional output directive 
            'if the user specifies it in the text template.
            '---------------------------------------------------------------------
            Public Sub SetOutputEncoding(ByVal encoding As System.Text.Encoding, ByVal fromOutputDirective As Boolean) Implements ITextTemplatingEngineHost.SetOutputEncoding
    
                fileEncodingValue = encoding
            End Sub
    
    
            'The engine calls this method when it is done processing a text
            'template to pass any errors that occurred to the host.
            'The host can decide how to display them.
            '---------------------------------------------------------------------
            Public Sub LogErrors(ByVal errors As System.CodeDom.Compiler.CompilerErrorCollection) Implements ITextTemplatingEngineHost.LogErrors
    
                errorsValue = errors
            End Sub
    
    
            'This is the application domain that is used to compile and run
            'the generated transformation class to create the generated text output.
            '----------------------------------------------------------------------
            Public Function ProvideTemplatingAppDomain(ByVal content As String) As System.AppDomain Implements ITextTemplatingEngineHost.ProvideTemplatingAppDomain
    
                'This host will provide a new application domain each time the 
                'engine processes a text template.
                '-------------------------------------------------------------
                Return AppDomain.CreateDomain("Generation App Domain")
    
                'This could be changed to return the current appdomain, but new 
                'assemblies are loaded into this AppDomain on a regular basis.
                'If the AppDomain lasts too long, it will grow indefintely, 
                'which might be regarded as a leak.
    
                'This could be customized to cache the application domain for 
                'a certain number of text template generations (for example, 10).
    
                'This could be customized based on the contents of the text 
                'template, which are provided as a parameter for that purpose.
            End Function
        End Class 'CustomCmdLineHost
    
    
        'This will accept the path of a text template as an argument.
        'It will create an instance of the custom host and an instance of the
        'text templating transformation engine. It will also transform the
        'template to create the generated text output file.
        '-------------------------------------------------------------------------
        Class Program
            Shared Sub Main(ByVal args As String())
                Try
                    ProcessTemplate(args)
    
                Catch ex As Exception
                    Console.WriteLine(ex.Message)
                End Try
            End Sub
    
            Shared Sub ProcessTemplate(ByVal args As String())
    
                Dim templateFileName As String = ""
    
                If args.Length = 0 Then
                    Throw New System.Exception("you must provide a text template file path")
                End If
    
                templateFileName = args(0)
    
                If templateFileName Is Nothing Then
                    Throw New ArgumentNullException("the file name cannot be null")
                End If
    
                If Not File.Exists(templateFileName) Then
                    Throw New FileNotFoundException("the file cannot be found")
                End If
    
                Dim host As CustomCmdLineHost = New CustomCmdLineHost()
                Dim engine As Engine = New Engine()
    
                host.TemplateFileValue = templateFileName
    
                'Read the text template.
                Dim input As String = File.ReadAllText(templateFileName)
    
                'Transform the text template.
                Dim output As String = engine.ProcessTemplate(input, host)
    
                Dim outputFileName As String = Path.GetFileNameWithoutExtension(templateFileName)
                outputFileName = Path.Combine(Path.GetDirectoryName(templateFileName), outputFileName)
                outputFileName = outputFileName & "1" & host.FileExtension
    
                File.WriteAllText(outputFileName, output, host.fileEncoding)
    
                Dim e As CompilerError
                For Each e In host.Errors
                    Console.WriteLine(e.ToString())
                Next
            End Sub 'ProcessTemplate
        End Class 'Program
    
    End Namespace
    
  4. For Visual Basic only, open the Project menu, and click CustomHost Properties. In the Startup object list, click CustomHost.Program.

  5. On the File menu, click Save All.

  6. On the Build menu, click Build Solution.

To test the custom host, first you must write a text template. Then you run the custom host, pass it the name of the text template, and verify that the template is transformed.

To create a text template to test the custom host

  1. Create a text file, and name it TestTemplate.txt.

    You can use any text editor (for example, Notepad) to create the file.

  2. Add the following to the file:

    NoteNote:

    The programming language of the text template does not need to match that of the custom host.

    Text Template Host Test
    
    <#@ template debug="true" #>
    
    <# //Uncomment this line to test that the host allows the engine to set the extension. #>
    <# //@ output extension=".htm" #>
    
    <# //Uncomment this line if you want to see the generated transformation class. #>
    <# //System.Diagnostics.Debugger.Break(); #>
    
    <# for (int i=0; i<3; i++)
       {
           WriteLine("This is a test");
       } 
    #>
    

    Text Template Host Test
    
    <#@ template debug="true" language="VB"#>
    
    <# 'Uncomment this line to test that the host allows the engine to set the extension. #>
    <# '@ output extension=".htm" #>
    
    <# 'Uncomment this line if you want to see the generated transformation class. #>
    <# 'System.Diagnostics.Debugger.Break() #>
    
    <# Dim i As Integer
       For i = 0 To 2
    
           WriteLine("This is a test")
       Next
    #>
    
  3. Save and close the file.

To test the custom host

  1. Open the Command Prompt window.

  2. Type the path of the executable file for the custom host, but do not press ENTER yet.

    For example, type:

    <YOUR PATH>CustomHost\bin\Debug\CustomHost.exe

    NoteNote:

    Instead of typing the address, you can browse to the file CustomHost.exe in Windows Explorer and then drag the file into the Command Prompt window.

  3. Type a space.

  4. Type the path of the text template file, and then press ENTER.

    For example, type:

    C:\<YOUR PATH>TestTemplate.txt

    NoteNote:

    Instead of typing the address, you can browse to the file TestTemplate.txt in Windows Explorer and then drag the file into the Command Prompt window.

    The custom host application runs and completes the text template transformation process.

  5. In Windows Explorer, browse to the folder that contains the file TestTemplate.txt.

    That folder also contains the file TestTemplate1.txt.

  6. Open this file to see the results of the text template transformation.

    The generated text output appears and looks like this:

    Text Template Host Test
    
    
    
    
    This is a test
    This is a test
    This is a test
    

For more information, see Security of Text Templates.

In this walkthrough, you created a text template transformation host that supports the basic transformation functionality. You can expand your host to support text templates that call custom or generated directive processors. For more information, see Walkthrough: Connecting a Host to a Generated Directive Processor.

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