我想使用 SplitViewNavigator 容器制作一个应用程序，其中包含左视图中的城市列表和右视图中有关城市的详细信息，在右视图中有一个文本输入，通过我获取城市名称并存储在 SQLite 数据库中，以及该名称应该从 SQLite 数据库添加到左侧视图中的列表我开始使用 Main.mxml 中的流动代码：
<?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>
我的 model.DataModel 是一个动作脚本类：
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;
}
}
}
我的 valueobject.CityValueObject 类是：
package valueobject
{
[Bindable]
public class CityValueObject
{
public var id:uint;
public var nameofcity:String;
}}
我的 uttillities.CityUtils 类是 ::
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";
}
}
}
我左边的城市列表是：
<?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>
最后我关于城市的显示详细信息是这样的：
<?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>
上面的视图（显示详细信息）仍在开发中，但在这个阶段我试图通过从城市名称输入文本输入中获取名称来将城市名称添加到城市列表中，但在：
statement.sqlConnection = sqlConnection; // Here error occurs saying that Error #1009: Cannot access a property or method of a null object reference.
我得到那个错误并且无法继续。
任何人都可以通过我上面的代码给我解决这个问题的方法，或者通过这个应用程序建议我另一种方法来满足我的需求提前谢谢...