http://www.infoq.com/cn/news/2009/11/T4-Multiple-Output
初次认识并尝试使用T4生成代码的时候,相关学习资料似乎比较少。不过现在VS2010 的MSDN里已有相关章节,可参看《代码生成和文本模板》章节。可以用C#的语法写模板,实在舒服很多。
很快就发现T4难以生成多个文件的缺陷,微软似乎也不着急改进这一点。通过搜索,从InfoQ找到一篇文章《用T4生成多个文件》,链接到一篇文章,Damien Guard的扩展可以方便的生成多个文件。原文是英文,能看懂,然而如果翻译则斟酌字词太辛苦。
首先,保存以下代码为一个模板文件(例如保存文件名为Manager.ttinclude):‘
<#@ assembly name="System.Core"#>
<#@ assembly name="System.Data.Linq"#>
<#@ assembly name="EnvDTE"#>
<#@ assembly name="System.Xml"#>
<#@ assembly name="System.Xml.Linq"#>
<#@ import namespace="System"#>
<#@ import namespace="System.CodeDom"#>
<#@ import namespace="System.CodeDom.Compiler"#>
<#@ import namespace="System.Collections.Generic"#>
<#@ import namespace="System.Data.Linq"#>
<#@ import namespace="System.Data.Linq.Mapping"#>
<#@ import namespace="System.IO"#>
<#@ import namespace="System.Linq"#>
<#@ import namespace="System.Reflection"#>
<#@ import namespace="System.Text"#>
<#@ import namespace="System.Xml.Linq"#>
<#@ import namespace="Microsoft.VisualStudio.TextTemplating"#>
<#+
// Manager class records the various blocks so it can split them up
class Manager {
private class Block {
public String Name;
public int Start, Length;
}
private Block currentBlock;
private List<Block> files = new List<Block>();
private Block footer = new Block();
private Block header = new Block();
private ITextTemplatingEngineHost host;
private StringBuilder template;
protected List<String> generatedFileNames = new List<String>();
public static Manager Create(ITextTemplatingEngineHost host, StringBuilder template) {
return (host is IServiceProvider) ? new VSManager(host, template) : new Manager(host, template);
}
public void StartNewFile(String name) {
if (name == null)
throw new ArgumentNullException("name");
CurrentBlock = new Block { Name = name };
}
public void StartFooter() {
CurrentBlock = footer;
}
public void StartHeader() {
CurrentBlock = header;
}
public void EndBlock() {
if (CurrentBlock == null)
return;
CurrentBlock.Length = template.Length - CurrentBlock.Start;
if (CurrentBlock != header && CurrentBlock != footer)
files.Add(CurrentBlock);
currentBlock = null;
}
public virtual void Process(bool split) {
if (split) {
EndBlock();
String headerText = template.ToString(header.Start, header.Length);
String footerText = template.ToString(footer.Start, footer.Length);
String outputPath = Path.GetDirectoryName(host.TemplateFile);
files.Reverse();
foreach(Block block in files) {
String fileName = Path.Combine(outputPath, block.Name);
String content = headerText + template.ToString(block.Start, block.Length) + footerText;
generatedFileNames.Add(fileName);
CreateFile(fileName, content);
template.Remove(block.Start, block.Length);
}
}
}
protected virtual void CreateFile(String fileName, String content) {
if (IsFileContentDifferent(fileName, content))
File.WriteAllText(fileName, content);
}
public virtual String GetCustomToolNamespace(String fileName) {
return null;
}
public virtual String DefaultProjectNamespace {
get { return null; }
}
protected bool IsFileContentDifferent(String fileName, String newContent) {
return !(File.Exists(fileName) && File.ReadAllText(fileName) == newContent);
}
private Manager(ITextTemplatingEngineHost host, StringBuilder template) {
this.host = host;
this.template = template;
}
private Block CurrentBlock {
get { return currentBlock; }
set {
if (CurrentBlock != null)
EndBlock();
if (value != null)
value.Start = template.Length;
currentBlock = value;
}
}
private class VSManager: Manager {
private EnvDTE.ProjectItem templateProjectItem;
private EnvDTE.DTE dte;
private Action<String> checkOutAction;
private Action<IEnumerable<String>> projectSyncAction;
public override String DefaultProjectNamespace {
get {
return templateProjectItem.ContainingProject.Properties.Item("DefaultNamespace").Value.ToString();
}
}
public override String GetCustomToolNamespace(string fileName) {
return dte.Solution.FindProjectItem(fileName).Properties.Item("CustomToolNamespace").Value.ToString();
}
public override void Process(bool split) {
if (templateProjectItem.ProjectItems == null)
return;
base.Process(split);
projectSyncAction.EndInvoke(projectSyncAction.BeginInvoke(generatedFileNames, null, null));
}
protected override void CreateFile(String fileName, String content) {
if (IsFileContentDifferent(fileName, content)) {
CheckoutFileIfRequired(fileName);
File.WriteAllText(fileName, content);
}
}
internal VSManager(ITextTemplatingEngineHost host, StringBuilder template)
: base(host, template) {
var hostServiceProvider = (IServiceProvider) host;
if (hostServiceProvider == null)
throw new ArgumentNullException("Could not obtain IServiceProvider");
dte = (EnvDTE.DTE) hostServiceProvider.GetService(typeof(EnvDTE.DTE));
if (dte == null)
throw new ArgumentNullException("Could not obtain DTE from host");
templateProjectItem = dte.Solution.FindProjectItem(host.TemplateFile);
checkOutAction = (String fileName) => dte.SourceControl.CheckOutItem(fileName);
projectSyncAction = (IEnumerable<String> keepFileNames) => ProjectSync(templateProjectItem, keepFileNames);
}
private static void ProjectSync(EnvDTE.ProjectItem templateProjectItem, IEnumerable<String> keepFileNames) {
var keepFileNameSet = new HashSet<String>(keepFileNames);
var projectFiles = new Dictionary<String, EnvDTE.ProjectItem>();
var originalFilePrefix = Path.GetFileNameWithoutExtension(templateProjectItem.get_FileNames(0)) + ".";
foreach(EnvDTE.ProjectItem projectItem in templateProjectItem.ProjectItems)
projectFiles.Add(projectItem.get_FileNames(0), projectItem);
// Remove unused items from the project
foreach(var pair in projectFiles)
if (!keepFileNames.Contains(pair.Key) && !(Path.GetFileNameWithoutExtension(pair.Key) + ".").StartsWith(originalFilePrefix))
pair.Value.Delete();
// Add missing files to the project
foreach(String fileName in keepFileNameSet)
if (!projectFiles.ContainsKey(fileName))
templateProjectItem.ProjectItems.AddFromFile(fileName);
}
private void CheckoutFileIfRequired(String fileName) {
var sc = dte.SourceControl;
if (sc != null && sc.IsItemUnderSCC(fileName) && !sc.IsItemCheckedOut(fileName))
checkOutAction.EndInvoke(checkOutAction.BeginInvoke(fileName, null, null));
}
}
} #>
接着,在T4模板文件里引用这个模板,并声明一个Manager类实例:
<#@ template language="C#" hostspecific="True"#>
<#@include file="Manager.ttinclude"#>
<# var manager = Manager.Create(Host, GenerationEnvironment); #>
使用两行代码可使代码输出到单独文件,你要输出的代码可写在这两个语句中间,StartNewFile的参数就是输出的文件名:
<# manager.StartNewFile("Employee.generated.cs"); #>
<# manager.EndBlock(); #>
比如可以这样写:
<# manager.StartNewFile("Employee.generated.cs"); #>
public class Employee { }
<# manager.EndBlock(); #>
还可以为每个输出文件输出同样的头部或顶部,只需要相应的语句:
<# manager.StartHeader(); #>
// Code generated by a template
using System;
<# manager.EndBlock(); #>
<# manager.StartFooter(); #>
// It's the end
<# manager.EndBlock(); #>
最后使用这句来执行输出多个文件: