arcgis api for flex求线段的起点，终点和中点
求线段的中点:
先获取Polyline最中间的path，然后再得到这个path的中间点作为整个Polyline的中点

private function getCenter(pl：Polyline):MapPoint{    var pathCount:Number=pl.paths.length;    var pathIndex:int=int((pathCount / 2) - 1);    var midPath:Array=pl.paths[pathIndex];    var ptCount:Number=midPath.length;    var ptIndex:int=int((ptCount / 2) - 1);    var pt:MapPoint=pl.getPoint(pathIndex, ptIndex);    return pt;}

var xx:int=LuduanList.selectedIndex;var myGraphic:Graphic=GraphicArr[xx];var l:Polyline=myGraphic.geometry as Polyline;var goldPath:Array=l.paths[l.paths.length-1];var spt:MapPoint=l.getPoint(0,0);var mpt:MapPoint=l.getPoint(l.paths.length-1,goldPath.length-1);