angularjs下拉框空白的解决办法

<select class="form-control" ng-model="userstate"
  ng-init="userstate=0">
 <option value="-1">选择状态</option>
 <option value="0">在职</option>
 <option value="1">离职</option>

 </select>

app.directive("dmodel",function () {
  return {
   restrict:'a',
   compile:function(element, attrs, transclude){
    console.log(transclude);
    var dmodel=attrs["dmodel"];
    return{
     pre:function(scope, ielement, iattrs){

      var selectvalue=scope[dmodel]+"";
      if(selectvalue)
      {
       var options=element.children();
       for(var i=0;i<options.length;i++)
       {
        if(selectvalue==options[i].value)
        {
         options[i].setattribute("selected",true);
         break;
        }
       }
      }
     },
     post:function(scope, ielement, iattrs){
      element.on("change",function () {
       var selectvalue=this.value;
       scope.$apply(function () {
        scope[dmodel]= selectvalue;
       });
      })
     }
    }
   }

  }
 });