AngularJs + TypeScript：如何实现如果条件在角控制器

Question

我想实现一个if else条件角控制器。我采取了下拉和其索引更改我绑定我的另一个下降。我试过NG-如果太多，但它会隐藏整个下拉，我想下拉可见。这里是我的html代码： -

<div data-ng-app="CustomerNew" data-ng-controller="CreateCustomerCtrl as custom" ng-init="getFormData();"> 
<table style="width: 144% ! important;" class="TableStyle1" id="Table1" cellspacing="0" cellpadding="2" border="0"> 
    <tr> 
     <td>Billing Type:</td> 
     <td> 
      <select id="listBillingType" ng-change="listBillingTypeselectedindexchange(custom.listBillingType)" data-ng-options="blngtype as blngtypee for (blngtype,blngtypee) in listBillingType" data-ng-model="custom.listBillingType" style="width: 182px !important; height: 34px;"> 
       <option value="">Choose an option {{optional ? '(optional)' : ''}}</option> 
      </select> 
     </td> 
    </tr> 

我正努力以填充上述下拉指数的基础上，另一种下拉。

<tr> 
    <td nowrap style="height: 26px">Parent Account:</td> 
    <td style="height: 26px"> 
     <select id="listParentAccount" data-ng-options="prntact as prntact.AccountNumber +' - '+ prntact.FullName for prntact in listParentAccount" ng-model="custom.listParentAccount" style="width: 182px !important; height: 34px;"> 
      <option value="">Choose an option {{optional ? '(optional)' : ''}}</option> 
     </select> 
    </td> 
</tr> 

这里是我的控制器

module CustomerNew.controllers { 
    export class CreateCustomerCtrl { 
     static $inject = ['$scope', '$http', '$templateCache']; 
     debugger; 
     constructor(protected $scope: ICustomerScope, 
     protected $http: ng.IHttpService, 
     protected $templateCache: ng.ITemplateCacheService) { 
      $scope.listBillingTypeselectedindexchange = this.listBillingTypeselectedindexchange; 
     } 
     public listBillingTypeselectedindexchange = (index) = > { 
      debugger; 
      var indexvalue = { 
       BillingTypesindex: index 
      } 
      if (index === "3" || index === "4" || index === "5") this.$http.put(dolistsalesindex, indexvalue). 
      success((data, status, headers, config) = > { 
       debugger; 
       this.$scope.listParentAccount = data["listParentAccount"]; 
      }). 
      error((data, status) = > { 
       debugger; 
       console.log("In Error:-in index"); 
       alert(data); 
      }); 
     } 
    } 

在这里，我想，如果选择的索引值3,4,5不仅仅是它会去我的API否则将返回空白。