flex 4.5 Mobile中的自定义着色错误

Question

当值 null 对象的属性，。在我的 as 文件中，当我调试时，我可以看到“数据”变量的值为 null一旦它调用超级构造函数就会给出这个错误。

我的动作脚本文件

public class ConditionalColoredLabelAS extends LabelItemRenderer 
{
    public function ConditionalColoredLabelAS() {
        if (data !=null)
        super();

    }

    // Use the value of the myColor property to draw 
    // the background color of the item in the list. 
    override protected function drawBackground(unscaledWidth:Number, unscaledHeight:Number):void {
        // Define a var to hold the color.
        var myColor:uint;
        if (data !=null)
        {
            // Determine the RGB color value from the label property.
        if (data == "red")
            myColor = 0xFF0000;
        if (data == "green")
            myColor = 0x00FF00;
        if (data == "blue")
            myColor = 0x0000FF;
        }
        //graphics.beginFill(myColor, 1);
        //graphics.drawRect(0, 0, unscaledWidth, unscaledHeight); 

    }
}

我从 mxml 文件中调用的是：

                <s:GridColumn id="name1" dataField="name" headerText="Name" />
                <s:GridColumn dataField="excess_return" headerText="Excess Return" itemRenderer="util.ConditionalColoredLabelAS"/>

错误是

TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at spark.components::Group/addElement()[E:\dev\4.5.1\frameworks\projects\spark\src\spark\components\Group.as:1342]
    at spark.components.gridClasses::GridLayout/createTypicalItemRenderer()[E:\dev\4.5.1\frameworks\projects\spark\src\spark\components\gridClasses\GridLayout.as:748]
    at spark.components.gridClasses::GridLayout/updateTypicalCellSizes()[E:\dev\4.5.1\frameworks\projects\spark\src\spark\components\gridClasses\GridLayout.as:883]
    at spark.components.gridClasses::GridLayout/measure()[E:\dev\4.5.1\frameworks\projects\spark\src\spark\components\gridClasses\GridLayout.as:444]
    at spark.components.supportClasses::GroupBase/measure()[E:\dev\4.5.1\frameworks\projects\spark\src\spark\components\supportClasses\GroupBase.as:1148]
    at mx.core::UIComponent/measureSizes()[E:\dev\4.5.1\frameworks\projects\framework\src\mx\core\UIComponent.as:8496]
    at mx.core::UIComponent/validateSize()[E:\dev\4.5.1\frameworks\projects\framework\src\mx\core\UIComponent.as:8420]
    at spark.components::Group/validateSize()[E:\dev\4.5.1\frameworks\projects\spark\src\spark\components\Group.as:1012]
    at mx.managers::LayoutManager/validateClient()[E:\dev\4.5.1\frameworks\projects\framework\src\mx\managers\LayoutManager.as:987]
    at mx.core::UIComponent/validateNow()[E:\dev\4.5.1\frameworks\projects\framework\src\mx\core\UIComponent.as:8067]
    at spark.components::ViewNavigator/commitNavigatorAction()[E:\dev\4.5.1\frameworks\projects\mobilecomponents\src\spark\components\ViewNavigator.as:1878]
    at spark.components::ViewNavigator/commitProperties()[E:\dev\4.5.1\frameworks\projects\mobilecomponents\src\spark\components\ViewNavigator.as:1236]
    at mx.core::UIComponent/validateProperties()[E:\dev\4.5.1\frameworks\projects\framework\src\mx\core\UIComponent.as:8209]
    at mx.managers::LayoutManager/validateProperties()[E:\dev\4.5.1\frameworks\projects\framework\src\mx\managers\LayoutManager.as:597]
    at mx.managers::LayoutManager/doPhasedInstantiation()[E:\dev\4.5.1\frameworks\projects\framework\src\mx\managers\LayoutManager.as:783]
    at mx.managers::LayoutManager/doPhasedInstantiationCallback()[E:\dev\4.5.1\frameworks\projects\framework\src\mx\managers\LayoutManager.as:1180]

Answer 1

终于找到答案了

功能是

private function returnItemRenderer( item: Object, column: GridColumn ): IFactory       

        {   
            if (item == null)
                return default_grid_item_renderer;

            //var field:String = column.dataField;
            if(item._return < 0)
                return red_grid_item_renderer;
            else if (item._return>0)
                return green_grid_item_renderer;
            return default_grid_item_renderer;  
            //return new ClassFactory( DefaultGridItemRenderer );         
        }   
    ]]>
</fx:Script>

声明是

<fx:Declarations> 
     <fx:Component id="default_grid_item_renderer" > 
         <s:DefaultGridItemRenderer /> 
     </fx:Component>
     <fx:Component id="red_grid_item_renderer" >
         <s:DefaultGridItemRenderer color="0xFF0000"/> 
     </fx:Component>
     <fx:Component id="green_grid_item_renderer" > 
         <s:DefaultGridItemRenderer color="0x00FF00"/>
    </fx:Component>
</fx:Declarations>

<s:DataGrid id="top5Grid" width="100%" height="100%"
                    dataProvider="{getDataResultMax.lastResult}">
            <s:columns>
                <s:ArrayList>

                    <s:GridColumn dataField="impact" headerText="Impact" itemRendererFunction="impactItemRenderer"/>
                    <s:GridColumn dataField="_return" headerText="Return" itemRendererFunction="returnItemRenderer"/>
                </s:ArrayList>      
            </s:columns>
        </s:DataGrid>