Checking that an item is selected in the Spark DropDownList control in Flex 4

The following example shows how you can check whether the user has selected an item in the Spark DropDownList control in Flex 4 by setting the Boolean requiresSelection property to true or using a NumberValidator to check the DropDownList control’s selectedIndex property is greater than -1.

The following example(s) require Flash Player 10 and the Adobe Flex 4 SDK. To download the Adobe Flash Builder 4 trial, see www.adobe.com/products/flex/. To download the latest nightly build of the Flex 4 SDK, see opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4.

For more information on getting started with Flex 4 and Flash Builder 4, see the official Adobe Flex Team blog.

<?xml version="1.0" encoding="utf-8"?> 
<!-- http://blog.flexexamples.com/2010/03/12/checking-that-an-item-is-selected-in-the-spark-dropdownlist-control-in-flex-4/ -->
<s:Application name="Spark_DropDownList_requiresSelection_test"
        xmlns:fx="http://ns.adobe.com/mxml/2009" 
        xmlns:s="library://ns.adobe.com/flex/spark" 
        xmlns:mx="library://ns.adobe.com/flex/mx"> 
    <s:layout>
        <s:HorizontalLayout horizontalAlign="center" verticalAlign="middle" />
    </s:layout>
 
    <s:DropDownList id="ddl" prompt="Please select an item" requireSelection="true">
        <s:dataProvider>
            <s:ArrayList source="[one,two,three,four,five,six,seven]" />
        </s:dataProvider>
    </s:DropDownList>
 
</s:Application>

View source is enabled in the following example.

Or you can use a NumberValidator on the Spark DropDownList control to check that the selectedIndex property is greater than or equal to 0, as seen in the following example:

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2010/03/12/checking-that-an-item-is-selected-in-the-spark-dropdownlist-control-in-flex-4/ -->
<s:Application name="Spark_DropDownList_selectedIndex_NumberValidator_test"
        xmlns:fx="http://ns.adobe.com/mxml/2009" 
        xmlns:s="library://ns.adobe.com/flex/spark" 
        xmlns:mx="library://ns.adobe.com/flex/mx"> 
    <s:layout>
        <s:HorizontalLayout horizontalAlign="center" verticalAlign="middle" />
    </s:layout>
 
    <fx:Script>
        <![CDATA[
            import mx.controls.Alert;
            import mx.events.ValidationResultEvent;
 
            protected function button1_clickHandler(evt:MouseEvent):void {
                numValidator.validate();
            }
 
            protected function numValidator_validHandler(evt:ValidationResultEvent):void {
                Alert.show("DropDownList item selected: " + ddl.selectedItem.toString(), evt.type);
            }
 
            protected function numValidator_invalidHandler(evt:ValidationResultEvent):void {
                Alert.show(ddl.prompt, evt.type);
            }
        ]]>
    </fx:Script>
 
    <fx:Declarations>
        <mx:NumberValidator id="numValidator"
                source="{ddl}"
                property="selectedIndex"
                minValue="0"
                lowerThanMinError="{ddl.prompt}"
                valid="numValidator_validHandler(event);"
                invalid="numValidator_invalidHandler(event);" />
    </fx:Declarations>
 
    <s:DropDownList id="ddl" prompt="Please select an item">
        <s:dataProvider>
            <s:ArrayList source="[one,two,three,four,five,six,seven]" />
        </s:dataProvider>
    </s:DropDownList>
 
    <s:Button label="validate" click="button1_clickHandler(event);" />
 
</s:Application>

View source is enabled in the following example.

This entry is based on a beta version of the Flex 4 SDK and therefore is very likely to change as development of the Flex SDK continues. The API can (and will) change causing examples to possibly not compile in newer versions of the Flex 4 SDK.

One thought on “Checking that an item is selected in the Spark DropDownList control in Flex 4

  1. For DropDownList checking selectedIndex = -1 for validation works great, on a ComboBox you need to check for >=0 because a user defined value shows up as selectedIndex -3

Comments are closed.