如何使用ng-messages显示Checkbox集和Radio set的错误消息？

I have been trying to validate Checkbox set and Radio set and show the error messages using ng-messages directive but it does not work out as expected. The ng-messages does not show the error message at all. I am populating error messages using an html file. Up until the errors are resolved, the submit button will be disabled in my form. I have been trying to validate Checkbox set and