無法與SplitViewNavigator容器配合使用

Question

我想使用SplitViewNavigator容器製作應用程序，其中包含左側視圖中的城市列表和右側視圖中城市的詳細信息，右側視圖中顯示的是通過我獲得的文本輸入應增加城市和存儲在SQLite數據庫，並對該名名稱從SQLite數據庫左視圖我開始在Main.mxml流動代碼列表：

<?xml version="1.0" encoding="utf-8"?> 
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
         xmlns:s="library://ns.adobe.com/flex/spark" 
         applicationDPI="160" 
         initialize="application1_initializeHandler(event)"> 
<fx:Script> 
    <![CDATA[ 
     import model.DataModel; 

     import mx.events.FlexEvent; 
     import valueobject.CityValueObject; 
     import utillities.CityUtils; 

     public var sqlConnection:SQLConnection; 
     protected var statement:SQLStatement; 
     protected function application1_initializeHandler(event:FlexEvent):void 
     { 
      sqlConnection = new SQLConnection(); 
      sqlConnection.open(File.applicationStorageDirectory.resolvePath("cityDB.db"), SQLMode.CREATE); 
      statement.sqlConnection = sqlConnection; // Here error occurs saying that Error #1009: Cannot access a property or method of a null object reference. 
      statement.text = "CREATE TABLE IF NOT EXISTS CITYNAME (" + 
       "id INTEGER PRIMARY KEY AUTOINCREMENT, " + 
       "nameofcity TEXT)"; 
      statement.execute(); 
      DataModel.getInstance().connection = sqlConnection; 

      CityUtils.getAllCities(); 
     } 

    ]]> 
</fx:Script> 
<fx:Declarations> 
    <!-- Place non-visual elements (e.g., services, value objects) here --> 
</fx:Declarations> 
<s:SplitViewNavigator id="svn" width="100%" height="100%"> 
    <s:ViewNavigator width="30%" height="100%" id="list_of_cities" firstView="views.ListOfCities"/> 
    <s:ViewNavigator width="70%" height="100%" id="display_contents" firstView="views.DisplayContents"/> 
</s:SplitViewNavigator> 

我model.DataModel是動作劇本類：

package model 
    { 
    import flash.data.SQLConnection; 

    import mx.collections.ArrayCollection; 

    [Bindable] 
    public class DataModel 
    { 
     public var connection:SQLConnection; 
     public var cityList:ArrayCollection = new ArrayCollection(); 
     public var logs:String="Application Logs........\n"; 

     public static var _instance:DataModel; 

     public function DataModel() 
     { 

     } 

     public static function getInstance():DataModel 
     { 
      if(_instance == null) 
      { 
       _instance = new DataModel(); 
      } 
      return _instance; 
     } 
    } 
} 

我valueobject.CityValueObject類是：

package valueobject 
{ 
[Bindable] 
public class CityValueObject 
{ 
    public var id:uint; 
    public var nameofcity:String; 
}} 

而且我uttillities.CityUtils類::

package utillities 
{ 
import flash.data.SQLResult; 
import flash.data.SQLStatement; 
import flash.display.Loader; 
import flash.display.LoaderInfo; 
import flash.events.Event; 
import flash.net.URLRequest; 
import flash.utils.ByteArray; 

import model.DataModel; 

import mx.collections.Sort; 
import mx.collections.SortField; 

import valueobject.CityValueObject; 


public class CityUtils 
{ 
    public static function getAllCities():void 
    { 
     var contactListStatement:SQLStatement = new SQLStatement(); 
     contactListStatement.sqlConnection = DataModel.getInstance().connection; 
     contactListStatement.text = "SELECT * FROM CITYNAME"; 
     contactListStatement.execute(); 
     var result:SQLResult = contactListStatement.getResult(); 
     if(result.data!=null) 
     { 
      DataModel.getInstance().cityList.removeAll(); 

      for(var count:uint=0;count<result.data.length;count++) 
      { 
       var cityVO:CityValueObject = new CityValueObject(); 
       cityVO.id = result.data[count].id; 
       cityVO.nameofcity = result.data[count].city;      
       DataModel.getInstance().cityList.addItem(cityVO); 
      } 
     } 
     sortData();  
    } 

    public static function sortData():void 
    { 
     var dataSortField:SortField = new SortField(); 
     dataSortField.name = "cityName"; 
     dataSortField.numeric = false; 

     /* Create the Sort object and add the SortField object created earlier to the array of fields to sort on. */ 
     var numericDataSort:Sort = new Sort(); 
     numericDataSort.fields = [dataSortField]; 

     /* Set the ArrayCollection object's sort property to our custom sort, and refresh the ArrayCollection. */ 
     DataModel.getInstance().cityList.sort = numericDataSort; 
     DataModel.getInstance().cityList.refresh(); 
    } 

    public static function updateLog(newLog:String):void 
    { 
     DataModel.getInstance().logs += new Date().time+" :-> "+newLog+"\n"; 
    } 
} 

}

我含城市的名單剩下的就是：

<?xml version="1.0" encoding="utf-8"?> 
<s:View xmlns:fx="http://ns.adobe.com/mxml/2009" 
    xmlns:s="library://ns.adobe.com/flex/spark" title="Cities" 
    > 
<fx:Declarations> 
    <!-- Place non-visual elements (e.g., services, value objects) here --> 
</fx:Declarations> 

<fx:Script> 
    <![CDATA[ 
     import model.DataModel; 

     import mx.collections.ArrayCollection; 
     import mx.events.FlexEvent; 
     import mx.events.IndexChangedEvent; 

     import spark.components.SplitViewNavigator; 
     import spark.components.ViewNavigator; 
     import spark.transitions.ViewTransitionBase; 
     protected function myList_changeHandler():void { 
      // Create a reference to the SplitViewNavigator. 
      var splitNavigator:SplitViewNavigator = navigator.parentNavigator as SplitViewNavigator; 

      // Create a reference to the ViewNavigator for the Detail frame. 
      var detailNavigator:ViewNavigator = splitNavigator.getViewNavigatorAt(1) as ViewNavigator; 

      detailNavigator.transitionsEnabled = false; 

      // Change the view of the Detail frame based on the selected List item. 
      detailNavigator.pushView(DisplayContents, list_of_cities.selectedItem);    
     }   
    ]]> 
</fx:Script> 
<s:VGroup width="100%" height="100%"> 
    <s:List id="list_of_cities" height="100%" width="100%" change="myList_changeHandler();" 
      dataProvider="{DataModel.getInstance().cityList}" labelField="nameofcity"> 

    </s:List>  
</s:VGroup> 

，並在有關城市最後我的顯示細節僅僅是這樣的：

<?xml version="1.0" encoding="utf-8"?> 
<s:View xmlns:fx="http://ns.adobe.com/mxml/2009" 
    xmlns:s="library://ns.adobe.com/flex/spark" title="Detail About City" 
    > 
<fx:Declarations> 
    <!-- Place non-visual elements (e.g., services, value objects) here --> 

</fx:Declarations> 
<s:actionContent> 
    <s:CalloutButton id="add_call_out_button" label="Add City" verticalPosition="after" 
        icon="@Embed('assets/add.png')" calloutDestructionPolicy="never"> 
     <!-- layout the callout content here --> 
     <s:calloutLayout> 
      <s:VerticalLayout paddingTop="10" paddingBottom="10" paddingLeft="10" paddingRight="10" horizontalAlign="center" gap="5"/> 
     </s:calloutLayout> 
     <s:calloutContent>    
      <s:TextInput id="city_name_input" prompt="Enter City Name" text="Sydney"/> 
      <s:HGroup gap="40"> 
       <s:Button id="add_city_name" label="Add City" width="150" height="40" click="add_city_name_clickHandler()"/> 
       <s:CheckBox id="preferred_cbox" label="Preferred" height="40" /> 
      </s:HGroup> 

     </s:calloutContent> 
    </s:CalloutButton> 
    <s:Button id="remove_city_name" label="Remove" width="120" height="40" 
       click="remove_city_name_clickHandler()" icon="@Embed('assets/delete.png')"/> 

</s:actionContent> 

<s:Label id="nameSomeThing" text="{data.Description}"/> 

<fx:Script> 
    <![CDATA[ 
     import model.DataModel; 

     import spark.components.SplitViewNavigator; 
     import spark.components.ViewNavigator; 

     protected function add_city_name_clickHandler():void 
     { 
      var sqlStatement:SQLStatement = new SQLStatement(); 
      sqlStatement.sqlConnection = DataModel.getInstance().connection; 
      sqlStatement.text = "INSERT INTO CITYNAME (nameofcity)" + 
           "VALUES(:nameofcity)"; 
      sqlStatement.parameters[":nameofcity"] = city_name_input.text; 
      sqlStatement.execute(); 

      var splitNavigator:SplitViewNavigator = navigator.parentNavigator as SplitViewNavigator; 

      // Create a reference to the ViewNavigator for the Detail frame. 
      var detailNavigator:ViewNavigator = splitNavigator.getViewNavigatorAt(1) as ViewNavigator; 

      detailNavigator.transitionsEnabled = false; 

      // Change the view of the Detail frame based on the selected List item. 
      detailNavigator.popToFirstView(); 
     } 

     protected function remove_city_name_clickHandler():void 
     { 
      // TODO Auto-generated method stub 

     } 

    ]]> 
</fx:Script> 

上述觀點（顯示詳細信息）仍然在發展，但在這個階段，我試圖增加城市從城市名稱輸入文本輸入，但在得到名字命名，以城市的名單：

statement.sqlConnection = sqlConnection; // Here error occurs saying that Error #1009: Cannot access a property or method of a null object reference. 

的iget的錯誤和不能夠繼續下去。

任何一個可以請給我通過我上面的代碼givien解決我這個問題的方法或建議我的另一種方式在推動這一應用感謝滿足我的需求......

Answer 1

隨着錯誤消息指出，statement爲空。

我沒有看到任何代碼將初始化它。 您需要：

statement = new SQLStament(); 

（我看不出有任何理由爲什麼這個變量將需要的application1_initializeHandler功能之外）。