如何在TextArea组件中获取插入符号的X，Y坐标？

public class TextAreaHelper
{
    public static function getCaretPosition(ta : TextArea) : Point
    {
        var flowComposer : StandardFlowComposer = StandardFlowComposer(ta.textFlow.flowComposer);
        var absoluteIndex : int = ta.selectionActivePosition;

        var lineIdx : int = flowComposer.findLineIndexAtPosition(absoluteIndex);
        if (lineIdx == flowComposer.numLines)
            lineIdx--;
        var prevLine : TextFlowLine = lineIdx != 0 ? flowComposer.getLineAt(lineIdx - 1) : null;
        var nextLine : TextFlowLine = lineIdx != flowComposer.numLines-1 ? flowComposer.getLineAt(lineIdx + 1) : null

        var result : Rectangle = flowComposer.getLineAt(lineIdx).computePointSelectionRectangle(absoluteIndex, ta, prevLine, nextLine, true);
        if (result)
        {
            var point : Point = new Point(result.x, result.y);
            point.x -= ta.scroller.viewport.horizontalScrollPosition;               
            point.y -= ta.scroller.viewport.verticalScrollPosition;
            return point;
        }
        return null;
    }
}




这是一个用法示例：



:<fx:Script>
    <![CDATA[
        [Bindable]
        private var caretPosition : Point;
        private function textareaSelectionChangeHandler(e : FlexEvent) : void
        {
            updateCaretPosition();
        }
        private function onPossibleScrollPositionChange(e : PropertyChangeEvent) : void
        {
            if (["verticalScrollPosition", "horizontalScrollPosition"].indexOf(e.property) != -1)
            {
                updateCaretPosition();
            }
        }
        private function updateCaretPosition() : void
        {
            caretPosition = TextAreaHelper.getCaretPosition(ta);
            if (caretPosition) caretPosition = ta.localToGlobal(caretPosition);
            trace(ObjectUtil.toString(caretPosition));
        }

        private function initTextArea() : void
        {
            ta.addEventListener(FlexEvent.SELECTION_CHANGE, textareaSelectionChangeHandler);
            ta.textDisplay.addEventListener(PropertyChangeEvent.PROPERTY_CHANGE, onPossibleScrollPositionChange);
        }

    ]]>
</fx:Script>
<s:TextArea x="200" y="300" id="ta" creationComplete="initTextArea()" />

<s:Rect x="{caretPosition.x}" y="{caretPosition.y}" width="10" height="10" visible="{caretPosition != null}">
    <s:fill>
        <s:SolidColor color="yellow" />
    </s:fill>
</s:Rect>