ArcGIS api for javascript——使用图层定义显示地图

描述

本例展示如何使用图层定义来限制显示在地图上的图层信息。为了了解本例做了什么，看看用于这个地图的ESRI_Census_USA服务的服务目录页是有帮助的。检查地图中的图层列表。现在注意这行代码限制了显示图层为州和县。

dynamicMapServiceLayer.setVisibleLayers([5,4,3]);

这个数据覆盖了美国，那么为什么当运行示例时仅仅Kansas周被显示？这是因为图层定义，通过SQL表达式限制数据在地图上的显示。本例中，图层定义限制了州为Kansas并且Kansas中的区县人口超过25000。

下面的代码增加图层定义到数组，然后使用 ArcGISDynamicMapServiceLayer.setLayerDefinitions()方法应用这些定义。注意在数组中，定义的索引和地图中图层的索引匹配:

var layerDefs = [];

layerDefs[5] = "STATE_NAME='Kansas'";

layerDefs[4] = "STATE_NAME='Kansas' and POP2007>25000";

layerDefs[3] = "STATE_NAME='Kansas' and POP2007>25000";

dynamicMapServiceLayer.setLayerDefinitions(layerDefs);

关于建立SQL表达式的帮助资源，见ArcGIS Desktop帮助里的About building an SQL expression 。

注意不能在 ArcGISTiledMapServiceLayers上设置图层定义。这些图层使用预先渲染的图片切片的缓存。虽然切片地图服务更快，但是被限制在切片上查看地图图片。

 1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 2 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
 3 <html>
 4   <head>
 5     <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
 6     <meta http-equiv="X-UA-Compatible" content="IE=7" />
 7     <title>动态创建图层列表</title>
 8     <link rel="stylesheet" type="text/css" href="http://serverapi.arcgisonline.com/jsapi/arcgis/1.6/js/dojo/dijit/themes/tundra/tundra.css">
 9     <script type="text/javascript" src="http://serverapi.arcgisonline.com/jsapi/arcgis/?v=1.6"></script>
10     <script type="text/javascript">
11         dojo.require("esri.map");
12         
13         var dynamicMapServiceLayer,map,visible = [];
14         
15         function init() {
16             map = new esri.Map("map");
17             
18             dynamicMapServiceLayer = new esri.layers.ArcGISDynamicMapServiceLayer(
19                 "http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer"
20             );
21             
22             if (dynamicMapServiceLayer.loaded) {        
23                 buildLayerList(dynamicMapServiceLayer);              
24             }else{
25                 dojo.connect(dynamicMapServiceLayer,"onLoad",buildLayerList);
26             }       
27         }
28         
29         function buildLayerList(layer) {
30             var infos = layer.layerInfos, info;
31             var items = [];
32             for (var i=0,j=infos.length;i<j;i++) {
33                 info = infos[i];
34                 if (info.defaultVisibility) {
35                     visible.push(info.id);
36                 }
37                 items[i] = "<input type='checkbox' class='list_item' checked='" + (info.defaultVisibility ? "checked" : "") + "' id='" + info.id +"' onclick='updateLayerVisibility();'/><label for='" +info.id+ "'>" +info.name+ "</label>";          
38             }
39             dojo.byId("layer_list").innerHTML = items.join();
40             
41             layer.setVisibleLayers(visible);
42             map.addLayer(layer);
43         
44         }
45         
46         function updateLayerVisibility() {
47             var inputs = dojo.query(".list_item"), input;
48             visible = [];
49             for (var i=0,j=inputs.length;i<j;i++) {
50                 if(inputs[i].checked) {
51                     visible.push(inputs[i].id);
52                 }           
53             }
54             dynamicMapServiceLayer.setVisibleLayers(visible);
55         
56         }
57         dojo.addOnLoad(init);
58     
59     </script>
60 
61   </head>
62 
63   <body >
64       This sample loads an ArcGISDynamicMapServiceLayer.<br />
65     It determines the layers in the map service and presents them as checkboxes that can be used to toggle their visibility.<br />
66     <br />
67       Layer List: <span id="layer_list"></span><br />
68       <br />
69       <div id="map" class="tundra" style=" 900px;height: 600px;border: 1px solid #000"></div>
70   </body>
71 </html>