How to stop T4 from executing every time I switch to another tab?

T4 is connected to the custom tool mechanism (IVsSingleFileGenerator) in the C#/VB project systems, which gives it the run on save, run custom tool menu and also the run on tab switching behavior - all for the price of implementing a simple interface.

Unfortunately this means that T4 also has essentially no control over those behaviors, which are the standard for custom tools.

An alternative may be to use the T4 MsBuild support in the VS Modeling and Visualization SDK to do T4 at build time and then disable the custom tool. I'll enquire with my colleague who built the msbuild support if it uses the custom tool to identify the set of templates or not and post back to the thread.

I had the exact same issue. I followed the steps in this article http://msdn.microsoft.com/en-us/library/ee789839.aspx about splitting off the templates into another project and sharing the output files.

It details how to switch off the TextTemplatingFileGenerator tool attached to the template by right clicking the template and clearing the CustomTool property. This stops the template generating code when saved ... but it STILL RUNS when switching tabs!

I think the only way to get round this would be to move all your template code into a new file with a different suffix (like ttinclude or t4 or something) and then include this file in your actual T4 template file using the include directive. That way you will never need to open that file to edit the template so it wont run by accident.

So in one file called MyTemplate.tt:

<#@ template language="VB" debug="false" hostspecific="true"#>
<#@ include file="Include\MyTemplateCodeBehind.t4" #>
<#@ output extension=".vb"#>
<# ' Nothing to see here! #>

Whilst in the other file called MyTemplateCodeBehind.t4:

<#@ template language="VB" debug="false" hostspecific="true"#>
<#
   For Each something In somecollection
#>
   <#= something.PrintMyCode() #>
<#
   Next

#>