Angular.js programmatically setting a form field to dirty

In your case, $scope.myForm.username.$setViewValue($scope.myForm.username.$viewValue); does the trick - it makes both the form and the field dirty, and appends appropriate CSS classes.

Just to be honest, I found this solution in new post in the topic from the link from your question. It worked perfectly for me, so I am putting this here as a standalone answer to make it easier to be found.

EDIT:

Above solution works best for Angular version up to 1.3.3. Starting with 1.3.4 you should use newly exposed API method $setDirty() from ngModel.NgModelController.

Since AngularJS 1.3.4 you can use $setDirty() on fields (source). For example, for each field with error and marked required you can do the following:

angular.forEach($scope.form.$error.required, function(field) {
    field.$setDirty();
});