The addCustomCheckBoxIsActive() function does not have the data fields in its scope to be used like this. However, you can pass the data field value (IsActive) as parameter when calling it from inside the client template.
More information about executing code inside client templates is available at:
If you want to have a reusable Grid including its datasource, probably it is worth considering using it as a partial view, not as a custom HtmlHelper. This discussion, however, is related to personal preferences, general programming techniques and best practices, and has entered the scope of our premium support services.
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