敲除手動訂閱不會觸發下拉更改

我基本上是試圖實現級聯下拉。前些天我請求幫助解決我複雜的JSON（這是來自CakePHP控制器的。我前些天收到的幫助非常好，但我遇到了另一個小問題。

我遇到的問題是我在調用JSON來獲取國家列表後，我更新了viewModel，一旦我填充下拉列表，我希望顯示縣的列表，並最終顯示一個城市列表，但我還沒有到那裏。不幸的是，當我改變我從列表中選擇一個國家，我的observable不會觸發，我懷疑這是因爲我創建了this.selectedCountry = ko.observable()並使用映射進行更新，但我不知道這是一個什麼有效的選項。當然，我也可以成爲該標記：/

我有以下代碼

HTML：

<select id="countries" 
      data-bind=' 
       options: countries, 
       optionsValue : "Id", 
       optionsText: "country", 
       optionsCaption: "[Please select a country]", 
       value: selectedCountry'> 
</select> 

<select id="counties" 
       data-bind=' 
        options: selectedCountry() ? counties : null, 
        optionsValue : "Id", 
        optionsText: "County", 
        optionsCaption: "[Please select a county]", 
        value: selectedCounty, 
        visible: (counties() && counties().length > 0)'> 
     </select>

的Javascript

var countryData= {"countries":[{"Country":{"id":"1","country":"England"}},{"Country":{"id":"2","country":"Wales\/Cymru"}},{"Country":{"id":"3","country":"Scotland"}},{"Country":{"id":"4","country":"Republic of Ireland"}},{"Country":{"id":"5","country":"Northern Ireland"}}]}; 

var countyData= {"country":[{"County":{"id":"1","county":"Essex"}}]}; 

var countryMappingOptions = { 
    'countries': { 
     'update': function (options) { 
      return ko.mapping.fromJS(options.data.Country); 
     }, 
     'ignore': ["selectedCountry"] 
    } 
}; 

var countyMappingOptions = { 
    'counties': { 
     'update': function (options) { 
      return ko.mapping.fromJS(options.data.County); 
     } 
    } 
}; 
     var vm= function() { 
      this.selectedCountry = ko.observable(); 
      this.selectedCounty = ko.observable(); 
      this.countries = ko.mapping.fromJS([]); 
      this.counties = ko.mapping.fromJS([]); 
      // Whenever the continent changes, reset the country selection 
      this.selectedCountry.subscribe(function (countryId) { 
       alert(countryId); 
       this.selectedCounty(undefined); 
       this.counties(undefined); 
       if (countryId != null) { 
        ko.mapping.fromJS(countyData, countyMappingOptions,this.viewModel); 
       } 
      }); 
      this.selectedCounty.subscribe(function (countryId) { 
       alert(countryId);  
      } .bind(this)); 
     }; 

     var viewModel = new vm(); 
     ko.applyBindings(viewModel); 
     console.log(viewModel .countries()); 
     ko.mapping.fromJS(countryData, countryMappingOptions ,viewModel); 
     console.log(viewModel .selectedCountry());

我還創建了一個的jsfiddle演示這裏的問題http://jsfiddle.net/jbrr5/21/

再次與這個問題的任何幫助將不勝感激，一旦我得到淘汰賽的一竅不通吧。

感謝

來源

2012-10-26 user1771329