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 =htt​​p://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>

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.