arcgis api for javascrip3.x geometry在地图显示不全

在遇到多个graphic显示到地图上时，会遇到显示不全问题，这是要修改显示范围，获取多个graphic的最小xmin、ymin。最大xmax、ymax。用获取的值最为显示范围。

if (dkAmount > 1) {
                    var xmax = [];
                    var ymax = [];
                    var xmin = [];
                    var ymin = [];
                    for (var i = 0; i < dkAmount; i++) {
                        var geometry = results.features[i].geometry;
                        var graphic = new esri.Graphic(geometry, fill);
                        cutGraphicLayer.add(graphic);
                        //先将多个graphic的值分别存入数组，再从数组中获取最大值、最小值
                        var graphic_extent = graphic.geometry.getExtent();
                        xmax.push(graphic_extent.xmax);
                        ymax.push(graphic_extent.ymax);
                        xmin.push(graphic_extent.xmin);
                        ymin.push(graphic_extent.ymin);
                    }
                    var xmax0 = xmax.sort(function (a, b) { return b - a; })[0] + 100;
                    var ymax0 = ymax.sort(function (a, b) { return b - a; })[0] + 100;
                    var xmin0 = xmin.sort(function (a, b) { return a - b; })[0] - 100;
                    var ymin0 = ymin.sort(function (a, b) { return a - b; })[0] - 100;
                    var visible_extent0 = new esri.geometry.Extent(xmin0, ymin0, xmax0, ymax0, new esri.SpatialReference({ wkid: mapwkid }));
                    map.setExtent(visible_extent0);
                    map.addLayer(cutGraphicLayer);
                }