Button never gets un-disabled - angularjs

Question

Second time I open this thread; had many answers on the last, but nobody gave an actual answer. My code is still not working and I'm beginning to think something very stupid is happening, or Angular is just not working properly.
This is my DOM, which I add through a directive:
<form ng-controller="controlFormulario as formCtrl">
<div style="width:50%; margin-left: 160px; margin-top: 2%">
<div class="form-group">
<label for="inputTitulo">Título</label>
<input type="titulo" class="form-control" id="inputTitulo" ng-model="formCtrl.formulario.titulo">
</div>
<div class="form-group">
<label for="inputTexto">Texto</label>
<textarea class="form-control" id="inputTexto" ng-model="formCtrl.formulario.texto"></textarea>
</div>
<div class="form-group">
<label for="fecha">Fecha</label>
<input type="fecha" class="form-control" id="fecha" ng-model="formCtrl.formulario.fecha" disabled>
</div>
<div class="form-group" >
<button ng-model="isDisabled" class="btn btn-primary" style="height:35px;width:100px;float:right;" ng-init="formCtrl.formulario.isDisabled = true" id="submit"
ng-disabled="isDisabled">
Enviar
</button>
</div>
</div>
</form>
And these are the controller and the directive:
var app = angular.module('app', []);
app.controller('controlFormulario', ['$scope', function($scope) {
var cf = this;
cf.formulario = [];
cf.formulario.fecha = new Date();
if(cf.formulario.texto != "" && cf.formulario.titulo != ""){
$scope.isDisabled = false;
} else {
$scope.isDisabled = true;
}
}]);
app.directive('formulario', [function() {
return {
restrict: 'E', // C: class, E: element, M: comments, A: attributes
templateUrl: 'modules/formulario.html',
controller: 'controlFormulario'
};
}]);
The thing I'm trying is pretty... easy? It's just getting the button active when some text is on the text and author inputs. Pretty straightforward, you know. Well, nothing is working.
Tried a normal ng-model binding to a previously written controller variable, like formCtrl.isDisabled. Didn't work.
Tried using the $scope (like now) and binding the ng-disabled attribute to the $scope.isDisabled variable. Didn't work.
Tried using a normal expression to write the "disabled" rule. Not an elegant fix, but it could work... so bad it didn't, either.
I'm getting a little frustrated to not being able to do such easy thing, so I guess I need some of your help to find out where I'm failing!

Answer 1

Well, you initialize $scope.isDisabled once, when the controller is instantiated, and never change it after. So, naturally, it keeps the same value forever.
Change
ng-disabled="isDisabled"
to
ng-disabled="isDisabled()"
and add the following function to the scope:
$scope.isDisabled = function() {
return cf.formulario.texto == "" || cf.formulario.titulo == "";
}
Also, note that you instantiate the controller twice for each directive instance:
once because the directive has
controller: 'controlFormulario'
and once because the template has
ng-controller="controlFormulario as formCtrl"
You should use one or the other, but not both.

Answer 2

Have you try to use ng-class :
<div ng-class="isDisabled ? 'class to Disabled':''">
I hope it 'll help you.

Answer 3

You can try this if you did not already tested :
For Dom :
<button ng-model="isDisabled" class="btn btn-primary" style="height:35px;width:100px;float:right;" ng-init="formCtrl.formulario.isDisabled = true" id="submit"
ng-disabled="FuncIsDisabled()">
And in controller you can make something like this :
function FuncIsDisabled(){
if(cf.formulario.texto != "" && cf.formulario.titulo != ""){
$scope.isDisabled = false;
} else {
$scope.isDisabled = true;
}
return $scope.isDisabled;// I'm not sure that this row is mandatory with the scope management
}