如何在更改输入约束后更新AngularJS中的表单控制器

我最近一直致力于动态更改表单上输入字段的约束.目的是制作一个后端驱动的表单,而所有字段及其约束都由服务器发送给我们.虽然我设法通过创建一个简单的指令来获得要添加/删除的约束,但似乎表单控制器没有获取这些更改,因此表单始终是$valid.看看 this jsfiddle,这是指令：

myApp.directive('uiConstraints',[function(){

function applyConstraints(element,newVal,oldVal){
    //remove old constraints
    if(oldVal !== undefined && oldVal !== null){
        for (var i = 0; i < oldVal.length; i++) {
            element.removeAttr(oldVal[i].key);
        }
    }

    //apply new constraints
    if(newVal !== undefined && newVal !== null){
        for (var i = 0; i < newVal.length; i++) {
            var constraint = newVal[i];
            element.attr(constraint.key,constraint.value);
        }
    }
}

function link(scope,element,attrs){
    scope.$watch(attrs.uiConstraints,function(newVal,oldVal){
        applyConstraints(element,oldVal);
    });
}

return {
    restrict : 'A',link : link
};

}]);

所需的行为是如此在official angularjs plunker上工作.但是,似乎在指令填充输入字段的约束之前创建FormController,并且更新这些约束不会更新FormController中的相应值.

any1是否知道我是否可以强制FormController获取指令所产生约束的更改？如果是这样,怎么样？我不知道从哪里开始……谢谢.

– 编辑 –
我无法找到工作人员(向他人展示我的最新变化)所以这里是我所拥有的jsfiddle：latest
更详细地描述了这个问题：

>转到描述的jsfiddle
>如果从文本框中删除初始值,它将变为红色(无效),但是控制器不会选择它并仍将显示：

myform.$valid = true
myform.myfield.$valid = true

– 编辑 –
赏金描述无法识别Stack Overflow格式(如新行等2个空格),所以这里的形式更易读：

Since this is still unsolved and interesting question I decided to start a bounty.
The requirements are:
– works on ancient AngularJS(1.0.3) and newer (if it can’t be done on 1.0.3 but someone did it on newer version of angular I will award bounty)
– initially a field has no constraints on it (is not required,max and min not set etc)
– at any time constraints for the field can change (it can become required,or a pattern for the value is set etc),as well as any existing constraints can be removed
– all constraints are stored in a controller in an object or array
– FormController picks up the changes,so that any $scope.FormName.$valid is being changed appropriately when constraints
on any fields in that form change

A good starting point is my 07003.
Thanks for your time and good luck!

.directive('uiConstraints',["$compile",function($compile) {
  function applyConstraints(element,oldVal) {
    //apply new constraints
    if (newVal !== undefined && newVal !== null) {
      for (var i = 0; i < newVal.length; i++) {
        var constraint = newVal[i];
        element.attr(constraint.key,constraint.value);
      }
    }
  }

  return {
    restrict: 'A',terminal: true,priority: 1000,require: "^form",link: function(scope,attrs,formController) {
      var templateElement;
      var previousTemplate;
      templateElement = element.clone(); //get the template element and store it 
      templateElement.removeAttr("ui-constraints");// remove the directive so that the next compile does not run this directive again
      previousTemplate = element;

      scope.$watch(attrs.uiConstraints,oldVal) {
        var clonedTemplate = templateElement.clone();
        applyConstraints(clonedTemplate,newVal);
        clonedTemplate.insertBefore(previousTemplate);

        var control = formController[previousTemplate.attr("name")];
        if (control){
           formController.$removeControl(control);
        }
        if (previousTemplate) {
          previousTemplate.remove();
        }

        $compile(clonedTemplate)(scope);
        previousTemplate = clonedTemplate;
      });
    }
  };
}]);