T4 运行时模板引擎
之前的文章都介绍的是通过保存的方式来使用T4，或者是通过VS下的TextTransform.exe文件来编译T4(还需要考虑传参长度等各种问题)T4模板引擎 参数调用；
这些方法都比较繁琐，可以适用在不同的使用场景下，本文介绍一下运行时的T4模板
运行时T4只需要在创建时候选择为运行时模板即可，和之前的模板引擎类型不同。
运行时T4生成工具为TextTemplatingFilePreprocessor，普通模板引擎是 TextTemplatingFileGenerator，需要注意区分。
模板引擎默认保存生成的是txt，运行时模板默认保存生成的是cs代码(生成与文件名一致的类)
运行时模板会在保存时生成对应的类
后续只需要调用这个TransformText方法就能获得生成的字符串结果。
例如
var page = new RuntimeTextTemplate1();
String pageContent = page.TransformText();
System.IO.File.WriteAllText(@"D:\work\code\outputPage.html", pageContent);
framework & .net core
framework下引用nuget: 【Microsoft.VisualStudio.TextTemplating】、【Microsoft.VisualStudio.TextTemplating.Interfaces】
.netcore下引用nuget:【Mono.TextTemplating】
另外替代方法可以通过安装【Microsoft.VisualStudio.SDK】,版本号为【17.0.31902.203】也可以正常获取依赖。
参数传递
运行时T4生成的代码是分部类，因此可以手动创建另外的代码来添加公共属性，然后在模板中使用
如果需要动态读取T4文件内容在运行时候执行代码,可以参考
https://learn.microsoft.com/zh-cn/visualstudio/modeling/walkthrough-creating-a-custom-text-template-host?view=vs-2022&tabs=csharp
核心内容为继承ITextTemplatingEngineHost,随后调用
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());
}
ITextTemplatingEngineHost实现代码文档中以给出,内容如下
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;
}
}
//Called by the Engine to enquire about
//the processing options you require.
//If you recognize that option, return an
//appropriate value.
//Otherwise, pass back NULL.
//--------------------------------------------------------------------
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());
}
}
}
}
此逻辑仅为基础的调用,如果需要传递参数则还需要继承ITextTemplatingSessionHost,
如果需要导入引用、程序集,则需要通过StandardAssemblyReferences、StandardImports这两个属性传递、调整后代码如下
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, ITextTemplatingSessionHost
{
//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; set;
} = new
List<string>()
{ 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;
set;
} = new List<string>() { "System" };
public ITextTemplatingSession Session { get; set; }
//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;
}
}
//Called by the Engine to enquire about
//the processing options you require.
//If you recognize that option, return an
//appropriate value.
//Otherwise, pass back NULL.
//--------------------------------------------------------------------
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.
}
public ITextTemplatingSession CreateSession()
{
return Session;
}
}
}
参数传递方法如下
CustomCmdLineHost host = new CustomCmdLineHost();
Engine engine = new Engine();
host.TemplateFileValue = $@"{ResourceHelper.TargetDir}{SelectTemplate.Path}";
//参数传递
var sessionHost = (ITextTemplatingSessionHost)host;
sessionHost.Session = new TextTemplatingSession();
sessionHost.Session.Add("ParameterName", base64Path);
//Read the text template.
string input = File.ReadAllText($@"{ResourceHelper.TargetDir}{SelectTemplate.Path}");
host.StandardAssemblyReferences.Add("Mono.TextTemplating.dll");
//Transform the text template.
string output = engine.ProcessTemplate(input, host);
尾注
如果需要在编译期间生成可以考虑使用Source Generate
留待后查，同时方便他人
联系我:renhanlinbsl@163.com
联系我:renhanlinbsl@163.com
