Angular ng-disabled is not working - angularjs

Question

Why is my button not enabling and disabling with this code:
<form name="formSendEmail" ng-submit="sendEmailAction();">
<div class="form-group">
<label class="label label-muted" for="visitorEmailForSendEmail">Visitor E-mail</label>
<input type="email" value="{{visitorDetail2.EmailAddress}}" id="visitorEmailForSendEmail" name="visitorEmailForSendEmail" class="form-control" ng-required="true" />
</div>
<input type="submit" class="btn btn-primary" value="Send E-mail" ng-disabled="formSendEmail.$invalid" />
</form>
Just above that code I have another form with a name of formCreateItinerary and I change my ng-disabled to point to that form; the enabling and disabling of the button works.
I have used this code too:
<input type="submit" class="btn btn-primary" value="Send E-mail" ng-disabled="visitorEmailForSendEmail == undefined || visitorEmailForSendEmail == ''" />
With this code, the button is disabled and does not enable. Can you help?

Answer 1

Try Changing the value="{{visitorDetail2.EmailAddress}}" to ng-model="visitorDetail2.EmailAddress"
<input type="email" ng-model="emailAddress" ng-change="validateEmail(emailAddress)" id="visitorEmailForSendEmail" name="visitorEmailForSendEmail" class="form-control" ng-required="true" />
<button ng-disabled="disableButton">button</button>
$scope.validateEmail=function(email) {
if(!validateEmail(email)){
$scope.disableButton=true;
}else{
$scope.disableButton=false;
}
}
function validateEmail(email) {
var re = /^(([^<>()\[\]\\.,;:\s#"]+(\.[^<>()\[\]\\.,;:\s#"]+)*)|(".+"))#((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
return re.test(email);
}