本文介绍了选择在Flex的DataGrid不通过的ValueObject到selectionChangeHandler功能的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我有一个TabNavigator容器，每个选项卡是一个模块。其中一个模块的标记单元和模块的全部code被张贴在这篇文章。
有几个问题：1）不填充从DataGrid中选择数据表格。2）选择行并点击删除给出了非常常见的错误：类型错误：错误＃1009：无法访问空对象引用的属性或方法在selectionChangeHandler函数中的ValueObject单元上的走线提供了空。为什么呢？
注：在其他模块（与TabNavigator的其他选项卡），我已经填充单元DropDownLists。这意味着该单元的ValueObject在其它模块中定义。然而，valueObjects应该是私有到模块，而不是共享。我不确定哪里出了问题来了。
完整模块code：
＆LT; XML版本=1.0编码=UTF-8＆GT？;
＆LT; S：模块的xmlns：FX =http://ns.adobe.com/mxml/2009
XMLNS：S =库：//ns.adobe.com/flex/spark
的xmlns：MX =库：//ns.adobe.com/flex/mx
的xmlns：unitservice =services.unitservice *。
的xmlns：valueObjects =valueObjects *。
宽度=724
高度=674＆GT;
＆LT; FX：样式源=财产/ CAaNDFlex.css/＆GT;
＆LT; FX：脚本＆GT;
＆LT;！[CDATA [
进口mx.controls.Alert;
进口mx.events.FlexEvent;
进口mx.rpc.events.ResultEvent;
进口spark.events.GridSelectionEvent;
保护功能unitsDg_creationCompleteHandler（事件：FlexEvent）：无效
{
getUnitsResult.token = unitservice.getUnits（）;
}
保护功能addBtn_clickHandler（事件：MouseEvent）方法：无效
{
currentState的=unitsAdd;
单位=新的单位（）;
}
保护功能unitsDg_selectionChangeHandler（事件：GridSelectionEvent）：无效
{
跟踪（event.currentTarget.selectedItem）; // Unit对象检测
跟踪（event.currentTarget.selectedItem为单位）; //空值
跟踪（单位）; //单位为NULL。为什么？
currentState的=unitsDetails;
}
保护功能button_clickHandler（事件：MouseEvent）方法：无效
{
跟踪（单位）; //单位为NULL。为什么？
unit.unitName = unitNameTextInput.text;
如果（unit.unitID == 0）
{
createUnitResult.token = unitservice.createUnit（单位）;
}
其他
{
updateUnitResult.token = unitservice.updateUnit（单位）;
}
}
保护功能updateBtn_clickHandler（事件：MouseEvent）方法：无效
{
currentState的=unitsUpdate;
}
保护功能createUnitResult_resultHandler（事件：的ResultEvent）：无效
{
currentState的=unitsDetails;
unit.unitID = event.result为INT;
unitsDg.dataProvider.addItem（单位）;
unitsDg.setSelectedIndex（unitsDg.dataProvider.getItemIndex（单位））;
unitsDg.ensureCellIsVisible（unitsDg.selectedIndex）;
}
保护功能deleteBtn_clickHandler（事件：MouseEvent）方法：无效
{
deleteUnitResult.token = unitservice.deleteUnit（unit.unitID）;
}
保护功能deleteUnitResult_resultHandler（事件：的ResultEvent）：无效
{
unitsDg.dataProvider.removeItemAt（unitsDg.selectedIndex）;
currentState的=单位;
}
]]≥
＆LT; / FX：脚本＆GT;
＆LT; S：国家＆GT;
＆LT; S：国名=单位/＆GT;
＆LT; S：国名=unitsDetails/＆GT;
＆LT; S：国名=unitsAdd/＆GT;
＆LT; S：国名=unitsUpdate/＆GT;
＆LT; / S：国家＆GT;
＆LT; FX：声明＆GT;
＆所述氏：的CallResponder的id =getUnitsResult
结果=单位= getUnitsResult.lastResult为单位/＆GT;
＆所述; unitservice：UnitService的id =unitservice
故障=Alert.show（event.fault.faultString +'\ N'+ event.fault.faultDetail）
showBusyCursor =真/＆GT;
＆LT; valueObjects：单位ID =单位/＆GT;
＆所述氏：的CallResponder的id =createUnitResult
结果=createUnitResult_resultHandler（事件）/＆GT;
＆LT; S：的CallResponder ID =updateUnitResult/＆GT;
＆LT; S：的CallResponder ID =deleteUnitResult结果=deleteUnitResult_resultHandler（事件）/＆GT;
＆LT;！ - 将非视觉元素（例如，服务，价值的物品）在这里 - ＆GT;
＆LT; / FX：声明＆GT;
＆LT; FX：绑定目标=单位来源=unitsDg.selectedItem为单位/＆GT;
＆所述氏：数据网格的id =unitsDg×=10Y =37
的creationComplete =unitsDg_creationCompleteHandler（事件）requestedRowCount =4
selectionChange =unitsDg_selectionChangeHandler（事件）＆GT;
＆LT; S：列＆GT;
＆LT; S：ArrayList的＆GT;
＆LT; S：的GridColumn的dataField =的unitName
HEADERTEXT =的unitName＆GT;
＆所述; /秒：的GridColumn＆GT;
＆LT; S：的GridColumn的dataField =unitID
HEADERTEXT =unitID＆GT;
＆所述; /秒：的GridColumn＆GT;
＆LT; / S：ArrayList的＆GT;
＆LT; / S：列＆GT;
＆所述氏：typicalItem＆GT;
＆LT; FX：对象unitID =unitID1
的unitName =unitName1＆GT;
＆LT; / FX：对象＆gt;
＆所述; /秒：typicalItem＆GT;
＆LT; S：AsyncListView列表={getUnitsResult.lastResult}/＆GT;
＆LT; / S：数据网格＆GT;
＆LT; S：按钮的ID =addBtnX =10Y =0的标签=添加点击=addBtn_clickHandler（事件）
的styleName =actionButton/＆GT;
＆LT; S：表includeIn =unitsAdd，unitsUpdate
X =10
Y =176
的defaultButton ={}键＆GT;
＆LT; S：FormItem中的标签=的unitName＆GT;
＆所述氏：的TextInput的id =unitNameTextInput
文本={unit.unitName}/＆GT;
＆LT; / S：的FormItem＆GT;
＆LT; S：按钮的ID =按钮
标签=添加
点击=button_clickHandler（事件）
label.unitsUpdate =更新/＆GT;
＆LT; / S：表＆GT;
＆LT; S：按钮的ID =updateBtnX =138Y =0的标签=更新点击=updateBtn_clickHandler（事件）/＆GT;
＆LT; S：按钮的ID =deleteBtnX =266Y =0的标签=删除点击=deleteBtn_clickHandler（事件）/＆GT;
＆所述氏：表单includeIn =unitsDetails×=10Y =176＆GT;
＆LT; S：FormItem中的标签=的unitName＆GT;
＆LT; S：标签ID =unitNameLabel文本={unit.unitName}/＆GT;
＆LT; / S：的FormItem＆GT;
＆LT; / S：表＆GT;
＆LT; / S：模块＆GT;
解决方案
该selectedObject没有成功铸造单位，这意味着它可能不是单位或前投一个子类。它铸造到机不能成为一个单元，除非它是一前。
I have a TabNavigator, and each tab is a Module. One of the modules is labelled Units and the full code of the module is posted in this post.
There are several problems:1) Forms are not populated with data from the datagrid selection.2) Selecting a row and clicking delete gives the very-common error: TypeError: Error #1009: Cannot access a property or method of a null object reference. A trace on the valueObject unit within the selectionChangeHandler function gives NULL. Why?
Note: In other modules (other tabs of the TabNavigator), I have DropDownLists populated with units. This means that the valueObject Unit is defined in the other modules. However, valueObjects should be private to modules, and not shared. I am unsure where the problem comes.
Full module code:
<?xml version="1.0" encoding="utf-8"?>
<s:Module xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx"
xmlns:unitservice="services.unitservice.*"
xmlns:valueObjects="valueObjects.*"
width="724"
height="674">
<fx:Style source="assets/CAaNDFlex.css"/>
<fx:Script>
<![CDATA[
import mx.controls.Alert;
import mx.events.FlexEvent;
import mx.rpc.events.ResultEvent;
import spark.events.GridSelectionEvent;
protected function unitsDg_creationCompleteHandler(event:FlexEvent):void
{
getUnitsResult.token=unitservice.getUnits();
}
protected function addBtn_clickHandler(event:MouseEvent):void
{
currentState="unitsAdd";
unit=new Unit();
}
protected function unitsDg_selectionChangeHandler(event:GridSelectionEvent):void
{
trace(event.currentTarget.selectedItem); //Unit object detected
trace(event.currentTarget.selectedItem as Unit); //NULL
trace(unit); // unit is NULL. Why?
currentState="unitsDetails";
}
protected function button_clickHandler(event:MouseEvent):void
{
trace(unit); // unit is NULL. Why?
unit.unitName=unitNameTextInput.text;
if (unit.unitID == 0)
{
createUnitResult.token=unitservice.createUnit(unit);
}
else
{
updateUnitResult.token=unitservice.updateUnit(unit);
}
}
protected function updateBtn_clickHandler(event:MouseEvent):void
{
currentState="unitsUpdate";
}
protected function createUnitResult_resultHandler(event:ResultEvent):void
{
currentState="unitsDetails";
unit.unitID=event.result as int;
unitsDg.dataProvider.addItem(unit);
unitsDg.setSelectedIndex(unitsDg.dataProvider.getItemIndex(unit));
unitsDg.ensureCellIsVisible(unitsDg.selectedIndex);
}
protected function deleteBtn_clickHandler(event:MouseEvent):void
{
deleteUnitResult.token = unitservice.deleteUnit(unit.unitID);
}
protected function deleteUnitResult_resultHandler(event:ResultEvent):void
{
unitsDg.dataProvider.removeItemAt(unitsDg.selectedIndex);
currentState="units";
}
]]>
</fx:Script>
<s:states>
<s:State name="units"/>
<s:State name="unitsDetails"/>
<s:State name="unitsAdd"/>
<s:State name="unitsUpdate"/>
</s:states>
<fx:Declarations>
<s:CallResponder id="getUnitsResult"
result="unit = getUnitsResult.lastResult as Unit"/>
<unitservice:UnitService id="unitservice"
fault="Alert.show(event.fault.faultString + '\n' + event.fault.faultDetail)"
showBusyCursor="true"/>
<valueObjects:Unit id="unit" />
<s:CallResponder id="createUnitResult"
result="createUnitResult_resultHandler(event)"/>
<s:CallResponder id="updateUnitResult"/>
<s:CallResponder id="deleteUnitResult" result="deleteUnitResult_resultHandler(event)"/>
<!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>
<fx:Binding destination="unit" source="unitsDg.selectedItem as Unit"/>
<s:DataGrid id="unitsDg" x="10" y="37"
creationComplete="unitsDg_creationCompleteHandler(event)" requestedRowCount="4"
selectionChange="unitsDg_selectionChangeHandler(event)">
<s:columns>
<s:ArrayList>
<s:GridColumn dataField="unitName"
headerText="unitName">
</s:GridColumn>
<s:GridColumn dataField="unitID"
headerText="unitID">
</s:GridColumn>
</s:ArrayList>
</s:columns>
<s:typicalItem>
<fx:Object unitID="unitID1"
unitName="unitName1">
</fx:Object>
</s:typicalItem>
<s:AsyncListView list="{getUnitsResult.lastResult}"/>
</s:DataGrid>
<s:Button id="addBtn" x="10" y="0" label="Add" click="addBtn_clickHandler(event)"
styleName="actionButton"/>
<s:Form includeIn="unitsAdd,unitsUpdate"
x="10"
y="176"
defaultButton="{button}">
<s:FormItem label="unitName">
<s:TextInput id="unitNameTextInput"
text="{unit.unitName}"/>
</s:FormItem>
<s:Button id="button"
label="Add"
click="button_clickHandler(event)"
label.unitsUpdate="Update"/>
</s:Form>
<s:Button id="updateBtn" x="138" y="0" label="Update" click="updateBtn_clickHandler(event)"/>
<s:Button id="deleteBtn" x="266" y="0" label="Delete" click="deleteBtn_clickHandler(event)"/>
<s:Form includeIn="unitsDetails" x="10" y="176">
<s:FormItem label="unitName">
<s:Label id="unitNameLabel" text="{unit.unitName}"/>
</s:FormItem>
</s:Form>
</s:Module>
解决方案
The selectedObject is not successfully casting to Unit, which means it probably wasn't Unit or a subclass prior to the cast. Casting it to Unit won't make it a Unit unless it was one before.
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