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DirectiveProcessor Class

The abstract base class for a concrete directive processor.

Namespace: Microsoft.VisualStudio.TextTemplating
Assembly: Microsoft.VisualStudio.TextTemplating (in microsoft.visualstudio.texttemplating.dll)

public abstract class DirectiveProcessor
public abstract class DirectiveProcessor
public abstract class DirectiveProcessor

The text template transformation process has two steps. In the first step, the text template transformation engine creates a class that is referred to as the generated transformation class. In the second step, the engine compiles and executes the generated transformation class, to produce the generated text output.

Directive processors work by adding code to the generated transformation class. You call directives from a text template, and after you call a directive, the rest of the code you write in your text template can rely on the functionality provided by the directive. You can write your own custom directive processors to provide custom functionality to text templates.

For more information, see Directive Processors.

The text template transformation engine will hold a singleton instance of any required DirectiveProcessor classes.

DirectiveProcessor implements a state machine.

For example, if a text template has three directive calls to the same directive processor, the engine will call the following methods in the following order:

The following example creates a custom directive processor. The custom directive processor contains a directive that reads an XML file. The directive stores the XML in an XmlDocument variable, and exposes the XmlDocument through a property.

For more information, see Walkthrough: Creating a Custom Directive Processor.

using System;
using System.CodeDom;
using System.CodeDom.Compiler;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Text;
using System.Xml;
using System.Xml.Serialization;
using Microsoft.VisualStudio.TextTemplating;

namespace CustomDP
{
    public class CustomDirectiveProcessor : DirectiveProcessor
    {
        //this buffer stores the code that is added to the 
        //generated transformation class after all the processing is done 
        //---------------------------------------------------------------------
        private StringBuilder codeBuffer;


        //Using a Code Dom Provider creates code for the 
        //generated transformation class in either Visual Basic or C#.
        //If you want your directive processor to support only one language, you
        //can hard code the code you add to the generated transformation class.
        //In that case, you do not need this field.
        //--------------------------------------------------------------------------
        private CodeDomProvider codeDomProvider;


        //this stores the full contents of the text template that is being processed
        //--------------------------------------------------------------------------
        private String templateContents;


        //These are the errors that occur during processing. The engine passes 
        //the errors to the host, and the host can decide how to display them,
        //for example the the host can display the errors in the UI
        //or write them to a file.
        //---------------------------------------------------------------------
        private CompilerErrorCollection errorsValue;
        public new CompilerErrorCollection Errors
        {
            get { return errorsValue; }
        }


        //Each time this directive processor is called, it creates a new property.
        //We count how many times we are called, and append "n" to each new
        //property name. The property names are therefore unique.
        //-----------------------------------------------------------------------------
        private int directiveCount = 0;


        public override void Initialize(ITextTemplatingEngineHost host)
        {
            //we do not need to do any initialization work
        }


        public override void StartProcessingRun(CodeDomProvider languageProvider, String templateContents, CompilerErrorCollection errors)
        {
            //the engine has passed us the language of the text template
            //we will use that language to generate code later
            //----------------------------------------------------------
            this.codeDomProvider = languageProvider;
            this.templateContents = templateContents;
            this.errorsValue = errors;

            this.codeBuffer = new StringBuilder();
        }


        //Before calling the ProcessDirective method for a directive, the 
        //engine calls this function to see whether the directive is supported.
        //Notice that one directive processor might support many directives.
        //---------------------------------------------------------------------
        public override bool IsDirectiveSupported(string directiveName)
        {
            if (string.Compare(directiveName, "CoolDirective", StringComparison.OrdinalIgnoreCase) == 0)
            {
                return true;
            }
            if (string.Compare(directiveName, "SuperCoolDirective", StringComparison.OrdinalIgnoreCase) == 0)
            {
                return true;
            }
            return false;
        }


        public override void ProcessDirective(string directiveName, IDictionary<string, string> arguments)
        {
            if (string.Compare(directiveName, "CoolDirective", StringComparison.OrdinalIgnoreCase) == 0)
            {
                string fileName;

                if (!arguments.TryGetValue("FileName", out fileName))
                {
                    throw new DirectiveProcessorException("Required argument 'FileName' not specified.");
                }

                if (string.IsNullOrEmpty(fileName))
                {
                    throw new DirectiveProcessorException("Argument 'FileName' is null or empty.");
                }

                //Now we add code to the generated transformation class.
                //This directive supports either Visual Basic or C#, so we must use the
                //System.CodeDom to create the code.
                //If a directive supports only one language, you can hard code the code.
                //--------------------------------------------------------------------------

                CodeMemberField documentField = new CodeMemberField();

                documentField.Name = "document" + directiveCount + "Value";
                documentField.Type = new CodeTypeReference(typeof(XmlDocument));
                documentField.Attributes = MemberAttributes.Private;

                CodeMemberProperty documentProperty = new CodeMemberProperty();

                documentProperty.Name = "Document" + directiveCount;
                documentProperty.Type = new CodeTypeReference(typeof(XmlDocument));
                documentProperty.Attributes = MemberAttributes.Public;
                documentProperty.HasSet = false;
                documentProperty.HasGet = true;

                CodeExpression fieldName = new CodeFieldReferenceExpression(new CodeThisReferenceExpression(), documentField.Name);
                CodeExpression booleanTest = new CodeBinaryOperatorExpression(fieldName, CodeBinaryOperatorType.IdentityEquality, new CodePrimitiveExpression(null));
                CodeExpression rightSide = new CodeMethodInvokeExpression(new CodeTypeReferenceExpression("XmlReaderHelper"), "ReadXml", new CodePrimitiveExpression(fileName));
                CodeStatement[] thenSteps = new CodeStatement[] { new CodeAssignStatement(fieldName, rightSide) };

                CodeConditionStatement ifThen = new CodeConditionStatement(booleanTest, thenSteps);
                documentProperty.GetStatements.Add(ifThen);

                CodeStatement s = new CodeMethodReturnStatement(fieldName);
                documentProperty.GetStatements.Add(s);

                CodeGeneratorOptions options = new CodeGeneratorOptions();
                options.BlankLinesBetweenMembers = true;
                options.IndentString = "    ";
                options.VerbatimOrder = true;
                options.BracingStyle = "C";

                using (StringWriter writer = new StringWriter(codeBuffer, CultureInfo.InvariantCulture))
                {
                    codeDomProvider.GenerateCodeFromMember(documentField, writer, options);
                    codeDomProvider.GenerateCodeFromMember(documentProperty, writer, options);
                }

            }//end CoolDirective


            //One directive processor can contain many directives.
            //If you want to support more directives, the code goes here...
            //-----------------------------------------------------------------
            if (string.Compare(directiveName, "supercooldirective", StringComparison.OrdinalIgnoreCase) == 0)
            {
                //code for SuperCoolDirective goes here...
            }//end SuperCoolDirective


            //Track how many times the processor has been called.
            //-----------------------------------------------------------------
            directiveCount++;

        }//end ProcessDirective


        public override void FinishProcessingRun()
        {
            this.codeDomProvider = null;

            //important: do not do this:
            //the get methods below are called after this method 
            //and the get methods can access this field
            //-----------------------------------------------------------------
            //this.codeBuffer = null;
        }


        public override string GetPreInitializationCodeForProcessingRun()
        {
            //Use this method to add code to the start of the 
            //Initialize() method of the generated transformation class.
            //We do not need any pre-initialization, so we will just return "".
            //-----------------------------------------------------------------
            //GetPreInitializationCodeForProcessingRun runs before the 
            //Initialize() method of the base class.
            //-----------------------------------------------------------------
            return String.Empty;
        }


        public override string GetPostInitializationCodeForProcessingRun()
        {
            //Use this method to add code to the end of the 
            //Initialize() method of the generated transformation class.
            //We do not need any post-initialization, so we will just return "".
            //------------------------------------------------------------------
            //GetPostInitializationCodeForProcessingRun runs after the
            //Initialize() method of the base class.
            //-----------------------------------------------------------------
            return String.Empty;
        }


        public override string GetClassCodeForProcessingRun()
        {
            //Return the code to add to the generated transformation class.
            //-----------------------------------------------------------------
            return codeBuffer.ToString();
        }


        public override string[] GetReferencesForProcessingRun()
        {
            //This returns the references that we want to use when 
            //compiling the generated transformation class.
            //-----------------------------------------------------------------
            //We need a reference to this assembly to be able to call 
            //XmlReaderHelper.ReadXml from the generated transformation class.
            //-----------------------------------------------------------------
            return new string[]
            {
                "System.Xml",
                this.GetType().Assembly.Location
            };
        }


        public override string[] GetImportsForProcessingRun()
        {
            //This returns the imports or using statements that we want to 
            //add to the generated transformation class.
            //-----------------------------------------------------------------
            //We need CustomDP to be able to call XmlReaderHelper.ReadXml
            //from the generated transformation class.
            //-----------------------------------------------------------------
            return new string[]
            {
                "System.Xml",
                "CustomDP"
            };
        }
    }//end class CustomDirectiveProcessor


    //-------------------------------------------------------------------------
    // the code that we are adding to the generated transformation class 
    // will call this method
    //-------------------------------------------------------------------------
    public static class XmlReaderHelper
    {
        public static XmlDocument ReadXml(string fileName)
        {
            XmlDocument d = new XmlDocument();

            using (XmlTextReader reader = new XmlTextReader(fileName))
            {
                try
                {
                    d.Load(reader);
                }
                catch (System.Xml.XmlException e)
                {
                    throw new DirectiveProcessorException("Unable to read the XML file.", e);
                }
            }
            return d;
        }
    }//end class XmlReaderHelper
}//end namespace CustomDP
System.Object
  Microsoft.VisualStudio.TextTemplating.DirectiveProcessor
     Microsoft.VisualStudio.TextTemplating.RequiresProvidesDirectiveProcessor
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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