The following example shows how you can toggle data tips on a Flex PieChart control by setting the showDataTips property.

Full code after the jump.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/09/13/toggling-data-tips-on-a-piechart-in-flex/ -->
<mx:Application name="PieChart_showDataTips_test"
        xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:XMLListCollection id="dp">
        <mx:source>
            <mx:XMLList>
                <product label="Product 1" data="3" />
                <product label="Product 2" data="1" />
                <product label="Product 3" data="4" />
                <product label="Product 4" data="1" />
                <product label="Product 5" data="5" />
                <product label="Product 6" data="9" />
            </mx:XMLList>
        </mx:source>
    </mx:XMLListCollection>

    <mx:ApplicationControlBar dock="true">
        <mx:CheckBox id="checkBox"
                label="showDataTips:"
                labelPlacement="left"
                selected="true" />
    </mx:ApplicationControlBar>

    <mx:Panel styleName="opaquePanel"
            width="100%"
            height="100%">
        <mx:PieChart id="pieChart"
                dataProvider="{dp}"
                showDataTips="{checkBox.selected}"
                height="100%"
                width="100%">
            <mx:series>
                <mx:PieSeries id="pieSeries"
                        field="@data"
                        nameField="@label"
                        filters="[]" />
            </mx:series>
        </mx:PieChart>
        <mx:ControlBar width="100%">
            <mx:Legend dataProvider="{pieChart}"
                    direction="horizontal"
                    horizontalGap="100"
                    width="100%" />
        </mx:ControlBar>
    </mx:Panel>

</mx:Application>

View source is enabled in the following example.

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You can also set the showDataTips using ActionScript, as seen in the following example:

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/09/13/toggling-data-tips-on-a-piechart-in-flex/ -->
<mx:Application name="PieChart_showDataTips_test"
        xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            private function checkBox_change(evt:Event):void {
                pieChart.showDataTips = checkBox.selected;
            }
        ]]>
    </mx:Script>

    <mx:XMLListCollection id="dp">
        <mx:source>
            <mx:XMLList>
                <product label="Product 1" data="3" />
                <product label="Product 2" data="1" />
                <product label="Product 3" data="4" />
                <product label="Product 4" data="1" />
                <product label="Product 5" data="5" />
                <product label="Product 6" data="9" />
            </mx:XMLList>
        </mx:source>
    </mx:XMLListCollection>

    <mx:ApplicationControlBar dock="true">
        <mx:CheckBox id="checkBox"
                label="showDataTips:"
                labelPlacement="left"
                selected="true"
                change="checkBox_change(event);" />
    </mx:ApplicationControlBar>

    <mx:Panel styleName="opaquePanel"
            width="100%"
            height="100%">
        <mx:PieChart id="pieChart"
                dataProvider="{dp}"
                height="100%"
                width="100%">
            <mx:series>
                <mx:PieSeries id="pieSeries"
                        field="@data"
                        nameField="@label"
                        filters="[]" />
            </mx:series>
        </mx:PieChart>
        <mx:ControlBar width="100%">
            <mx:Legend dataProvider="{pieChart}"
                    direction="horizontal"
                    horizontalGap="100"
                    width="100%" />
        </mx:ControlBar>
    </mx:Panel>

</mx:Application>

Due to popular demand, here is the “same” example in a more ActionScript friendly format:

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/09/13/toggling-data-tips-on-a-piechart-in-flex/ -->
<mx:Application name="PieChart_showDataTips_test"
        xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        initialize="init();">

    <mx:Script>
        <![CDATA[
            import mx.charts.Legend;
            import mx.charts.PieChart;
            import mx.charts.series.PieSeries;
            import mx.collections.XMLListCollection;
            import mx.containers.ApplicationControlBar;
            import mx.containers.ControlBar;
            import mx.containers.Panel;
            import mx.containers.TileDirection;
            import mx.controls.ButtonLabelPlacement;
            import mx.controls.CheckBox;

            private var dp:XMLListCollection;
            private var checkBox:CheckBox;
            private var pieChart:PieChart;
            private var pieSeries:PieSeries;

            private function init():void {
                var productsXML:XML = <products>
                        <product label="Product 1" data="3" />
                        <product label="Product 2" data="1" />
                        <product label="Product 3" data="4" />
                        <product label="Product 4" data="1" />
                        <product label="Product 5" data="5" />
                        <product label="Product 6" data="9" />
                    </products>;
                dp = new XMLListCollection(productsXML.product);

                checkBox = new CheckBox();
                checkBox.label = "showDataTips:";
                checkBox.labelPlacement = ButtonLabelPlacement.LEFT;
                checkBox.selected = true;
                checkBox.addEventListener(Event.CHANGE, checkBox_change)

                var appControlBar:ApplicationControlBar;
                appControlBar = new ApplicationControlBar();
                appControlBar.dock = true;
                appControlBar.addChild(checkBox);
                addChildAt(appControlBar, 0);

                pieSeries = new PieSeries();
                pieSeries.field = "@data";
                pieSeries.nameField = "@label";
                pieSeries.filters = [];

                pieChart = new PieChart();
                pieChart.dataProvider = dp;
                pieChart.showDataTips = true;
                pieChart.percentWidth = 100;
                pieChart.percentHeight = 100;
                pieChart.series = [pieSeries];

                var legend:Legend = new Legend();
                legend.dataProvider = pieChart;
                legend.direction = TileDirection.HORIZONTAL;
                legend.setStyle("horizontalGap", 100);
                legend.percentWidth = 100;

                var panelControlBar:ControlBar = new ControlBar();
                panelControlBar.percentWidth = 100;
                panelControlBar.addChild(legend);

                var panel:Panel = new Panel();
                panel.styleName = "opaquePanel";
                panel.percentWidth = 100;
                panel.percentHeight = 100;
                panel.addChild(pieChart);
                panel.addChild(panelControlBar);
                addChild(panel);
            }

            private function checkBox_change(evt:Event):void {
                pieChart.showDataTips = checkBox.selected;
            }
        ]]>
    </mx:Script>

</mx:Application>