arcgis api for javascript如何遍历graphics

我想遍历我上传的SHP文件所形成的图形，不知道有什么问题,count不对，求指教

 function GetGraphicsArr() {
    var GraArr, GraStr, count = 0;
    for (var Gra in _Map.graphics) {
        if (Gra) {
            GraStr = JSON.stringify(Gra.geometry.toJson());
            GraArr.push(GraStr);
                        count++;
        } else {
                        alert("error");
        }
    }
    return count;
}

http://www.cnblogs.com/imihiroblog/p/3636782.html