Flex 4.6 dropDownList selectedIndex value set?

Question

我正在学习"一周内的Flex"教程，我已经到了他们在Flex中实现MVC模型的地步。在那之前一切都很好，但在视图中，他们使用dropDownList连接到dataProvider，并保留selectedIndex未声明（默认值为-1）。我（试着聪明一点！）试着将selectedIndex设置为0或1或任何其他数字。但什么都没发生，我怎么能这样做？

课程详情如下：

http://www.adobe.com/devnet/flex/videotraining/exercises/ex2_06.html

在我看来，代码的重要部分是：

主应用程序：

创建阵列：

            [Bindable]
            private var employees:ArrayCollection = new ArrayCollection();

此数组由httpservice:中的日期填充

                for each (var emp:Object in employeeData) 
                {
                    employee = new Employee();
                    employee.firstName = emp.firstName;
                    employee.lastName = emp.lastName; 
                    employee.id = emp.id; 
                    employee.title = emp.title; 
                    employee.email = emp.email; 
                    employee.managerID = emp.managerID; 
                    employee.department = emp.department; 
                    employee.location = emp.location; 
                    employee.deskLocation = emp.deskLocation; 
                    employee.city = emp.city; 
                    employee.state = emp.state; 
                    employee.countryCode = emp.countryCode; 
                    employee.postalCode = emp.postalCode; 
                    employee.directDial = emp.directDial; 
                    employee.hireDate = emp.hireDate; 
                    employee.evaluation = emp.evaluation; 
                    employee.phone = emp.phone;
                    employees.addItem(employee);
                }

以数组形式传递给自定义组件：

    <components:VehicleRequestForm employees="{employees}"/>

这个自定义表单捕获它并放入dropDownList，但selectedIndex似乎不起作用，它仍然默认为-1。我该怎么解决这个问题？（所有理想都受到赞赏）：

        <s:FormItem label="Employee:">
            <s:DropDownList id="dropDownList"
                            dataProvider="{employees}"
                            labelField="lastName"
                            selectedIndex="1"/>
        </s:FormItem>
        <s:FormItem label="Office Phone:">
            <s:TextInput id="phone"
                         text="{dropDownList.selectedItem.phone}"/>

ex2_08_solutions.mxm:

<?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" 
               xmlns:mx="library://ns.adobe.com/flex/mx" 
               minWidth="955" minHeight="850"
               creationComplete="employeeService.send()" 
               xmlns:components="components.*">
    <!-- Exercise 2.08: Creating an ArrayCollection of value objects -->
    <!-- Styles ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
    <fx:Style source="Styles.css"/>
    <!-- Script ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
    <fx:Script>
        <![CDATA[
            import mx.collections.ArrayCollection;
            import mx.controls.Alert;
            import mx.rpc.events.FaultEvent;
            import mx.rpc.events.ResultEvent;
            import valueObjects.Employee;
            // variable declarations ------------------------------------
            [Bindable]
            private var employees:ArrayCollection = new ArrayCollection();
            // getter/setters -------------------------------------------

            // helper methods -------------------------------------------

            // event handlers -------------------------------------------
            protected function employeeService_resultHandler(event:ResultEvent):void
            {
                var employeeData:ArrayCollection = event.result.employees.employee;
                var employee:Employee;
                for each (var emp:Object in employeeData) 
                {
                    employee = new Employee();
                    employee.firstName = emp.firstName;
                    employee.lastName = emp.lastName; 
                    employee.id = emp.id; 
                    employee.title = emp.title; 
                    employee.email = emp.email; 
                    employee.managerID = emp.managerID; 
                    employee.department = emp.department; 
                    employee.location = emp.location; 
                    employee.deskLocation = emp.deskLocation; 
                    employee.city = emp.city; 
                    employee.state = emp.state; 
                    employee.countryCode = emp.countryCode; 
                    employee.postalCode = emp.postalCode; 
                    employee.directDial = emp.directDial; 
                    employee.hireDate = emp.hireDate; 
                    employee.evaluation = emp.evaluation; 
                    employee.phone = emp.phone;
                    employees.addItem(employee);
                }
            }
            protected function employeeService_faultHandler(event:FaultEvent):void
            {
                Alert.show(event.fault.faultString,"Fault Information");    
            }
        ]]>
    </fx:Script>
    <!-- Declarations ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
    <fx:Declarations>
        <s:HTTPService id="employeeService"
                       url="http://adobetes.com/f45iaw100/remoteData/employees.xml"
                       result="employeeService_resultHandler(event)"
                       fault="employeeService_faultHandler(event)"/>
    </fx:Declarations>
    <!-- UI components ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
    <s:Label x="10" y="34" 
             width="690" height="40" 
             text="Employee Portal: Vehicle Request Form"
             styleName="titleHeader"/>
    <components:VehicleRequestForm employees="{employees}"/>
</s:Application>

车辆请求表单.mxml:

<?xml version="1.0" encoding="utf-8"?>
<s:Group xmlns:fx="http://ns.adobe.com/mxml/2009" 
         xmlns:s="library://ns.adobe.com/flex/spark" 
         xmlns:mx="library://ns.adobe.com/flex/mx"
         creationComplete="init()">
    <!-- Styles ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->

    <!-- Script ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
    <fx:Script>
        <![CDATA[
            // import statements ----------------------------------------
            import mx.collections.ArrayCollection;
            import mx.controls.Alert;
            import mx.events.CalendarLayoutChangeEvent;
            // variable declarations ------------------------------------
            [Bindable]
            public var employees:ArrayCollection;
            // getter/setters -------------------------------------------

            // helper methods -------------------------------------------

            // event handlers -------------------------------------------
            private function dateChangeHandler(event:CalendarLayoutChangeEvent):void
            {
                Alert.show('You have selected ' + event.target.selectedDate.toDateString());
                if ((event.target.id == "returnDate") && (pickupDate.selectedDate > returnDate.selectedDate)) 
                {
                    Alert.show("Pickup date must be scheduled before return date.");
                }
                if ((event.target.id == "pickupDate") && (pickupDate.selectedDate > returnDate.selectedDate) && (returnDate.selectedDate != null)) 
                {
                    Alert.show("Pickup date must be scheduled before return date.")
                }
            }
            private function init():void
            {
                pickupDate.addEventListener(CalendarLayoutChangeEvent.CHANGE, dateChangeHandler);
                returnDate.addEventListener(CalendarLayoutChangeEvent.CHANGE, dateChangeHandler);
            }
        ]]>
    </fx:Script>
    <!-- Declarations ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
    <fx:Declarations>
        <!-- Place non-visual elements (e.g., services, value objects) here -->
    </fx:Declarations>
    <!-- UI components ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -->
    <s:Form x="10" y="70">
        <s:FormItem label="Employee:">
            <s:DropDownList id="dropDownList"
                            dataProvider="{employees}"
                            labelField="lastName"
                            selectedIndex="1"/>
        </s:FormItem>
        <s:FormItem label="Office Phone:">
            <s:TextInput id="phone"
                         text="{dropDownList.selectedItem.phone}"/>
        </s:FormItem>
        <s:FormItem label="Mobile Phone:">
            <s:TextInput id="mobilePhone"/>
        </s:FormItem>
        <s:FormHeading label="Dates Requested"/>
        <s:FormItem label="Pickup Date:">
            <mx:DateChooser id="pickupDate"/>
        </s:FormItem>
        <s:FormItem label="Return Date:">
            <mx:DateChooser id="returnDate"/>
        </s:FormItem>
        <s:FormItem>
            <s:Button id="submitButton" 
                      label="Submit Request"/>
        </s:FormItem>
    </s:Form>
</s:Group>

Answer 1

不能将selectedIndex设置为不在dataProvider中的索引。实例化DropdownList时，dataProvider是一个空集合，因此1不是有效的选定索引。

填充集合后，请尝试设置selectedIndex。您可能需要在callLater中执行此操作（只要数据通常不是立即处理，而是在帧结束时处理。对于某些组件，这非常重要，对于其他组件，您可以忽略它）。

如果您只需要强制选择，请尝试将requireSelection设置为true。

更新（如何使用callLater）

protected function employeeService_resultHandler(event:ResultEvent):void{
            //...populating dataprovider
            callLater(function():void{
                if(dropDownList.dataProvider.length > wantedIndex){
                    dropDownList.selectedIndex=wantedIndex;
                }else{
                    Alert.show('can't select necessary index!','error')
                }
            });
}

Answer 2

你可以试试这个，

<s:DropDownList requireSelection="true" />

如果为true，则必须始终在控件中选择数据项。如果该值为true，则selectedIndex属性始终设置为介于0和（dataProvider.length-1）之间的值。