Access Visual Studio or other hosts from a text template

Article
01/12/2024

In a text template, you can use methods and properties that are exposed by the host that executes the template. Visual Studio is an example of a host.

Note

You can use host methods and properties in regular text templates, but not in preprocessed text templates.

Obtain access to the host

To access the host, set hostspecific="true" in the template directive. Now you can use this.Host, which has type ITextTemplatingEngineHost. The ITextTemplatingEngineHost type has members that you can use to resolve file names and log errors, for example.

Resolve File Names

To find the full path of a file relative to the text template, use this.Host.ResolvePath().

<#@ template hostspecific="true" language="C#" #>
<#@ output extension=".txt" #>
<#@ import namespace="System.IO" #>
<#
 // Find a path within the same project as the text template:
 string myFile = File.ReadAllText(this.Host.ResolvePath("MyFile.txt"));
#>
Content of myFile is:
<#= myFile #>

Display Error Messages

This example logs messages when you transform the template. If the host is Visual Studio, the errors are added to the Error List.

<#@ template hostspecific="true" language="C#" #>
<#@ output extension=".txt" #>
<#@ import namespace="System.CodeDom.Compiler" #>
<#
  string message = "test message";
  this.Host.LogErrors(new CompilerErrorCollection()
    { new CompilerError(
       this.Host.TemplateFile, // Identify the source of the error.
       0, 0, "0",   // Line, column, error ID.
       message) }); // Message displayed in error window.
#>

Use the Visual Studio API

If you're executing a text template in Visual Studio, you can use this.Host to access services provided by Visual Studio and any packages or extensions that are loaded.

Set hostspecific="true" and cast this.Host to IServiceProvider.

This example gets the Visual Studio API, DTE, as a service:

<#@ template hostspecific="true" language="C#" #>
<#@ output extension=".txt" #>
<#@ assembly name="EnvDTE" #>
<#@ import namespace="EnvDTE" #>
<#
 IServiceProvider serviceProvider = (IServiceProvider)this.Host;
 DTE dte = serviceProvider.GetService(typeof(DTE)) as DTE;
#>
Number of projects in this solution: <#=  dte.Solution.Projects.Count #>

Use hostSpecific with template inheritance

Specify hostspecific="trueFromBase" if you also use the inherits attribute, and if you inherit from a template that specifies hostspecific="true". If you don't, you might get a compiler warning that the property Host has been declared twice.

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