（转）Arcgis for JS之对象捕捉

http://blog.csdn.net/gisshixisheng/article/details/44098615

在web操作，如绘制或者测量的时候，为了精确，需要捕捉到某一图层的对象，在此，讲解下如何在Arcgis for JS中实现捕捉对象。
首先，在地图中添加一个graphiclayer：

gLayer = new GraphicsLayer();
map.addLayer(gLayer);

接着，在gLayer中添加几个对象：

map.on("load",function(){
    var items = geometry.item;
    gLayer.add(new Graphic(WktToPoint(items[0].wkt, {"wkid":4326}),sms));
    gLayer.add(new Graphic(WktToPolyline(items[1].wkt, {"wkid":4326}),sls));
    gLayer.add(new Graphic(WktToPolygon(items[2].wkt, {"wkid":4326}),sfs));
});

接下来，定义drawtoolbar以及绘制完成后的事件：

var drawToolbar = new esri.toolbars.Draw(map,{tooltip: "place text"});
drawToolbar.on("draw-end",showDrawResults);
function showDrawResults(evt){
    drawToolbar.deactivate();
    map.setMapCursor("default");
    var geometry = evt.geometry;
    map.graphics.add(new Graphic(geometry,sls));
};

接下来，定义一个Button，并添加button的click事件：

<button id="draw" style="z-index: 99;">绘制图形</button>

on(dom.byId("draw"), "click", function(){
    drawToolbar.activate(esri.toolbars.Draw.POLYLINE);
});

接下来定义map的捕捉设置：

var snapManager = map.enableSnapping({
    snapKey:has("mac") ? keys.META : keys.CTRL
});
var layerInfos = [{layer: gLayer}];
snapManager.setLayerInfos(layerInfos);

备注：

此处，需要调用的dojo包包括：

require([
    "esri/map",
    "esri/layers/GraphicsLayer",
    "esri/graphic",
    "esri/SnappingManager",
    "esri/sniff",

    "dojo/_base/event",
    "dojo/on",
    "dojo/dom",
    "dojo/keys",
    "dojo/domReady!"],
function(Map, GraphicsLayer, Graphic, Point, SnappingManager, has,
         event, on,dom, keys) {