正文
ArcGIS api for javascript——使用图层定义显示地图
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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。
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=7" />
<title>动态创建图层列表</title>
<link rel="stylesheet" type="text/css" href="http://serverapi.arcgisonline.com/jsapi/arcgis/1.6/js/dojo/dijit/themes/tundra/tundra.css">
<script type="text/javascript" src="http://serverapi.arcgisonline.com/jsapi/arcgis/?v=1.6"></script>
<script type="text/javascript">
dojo.require("esri.map"); var dynamicMapServiceLayer,map,visible = []; function init() {
map = new esri.Map("map"); dynamicMapServiceLayer = new esri.layers.ArcGISDynamicMapServiceLayer(
"http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer"
); if (dynamicMapServiceLayer.loaded) {
buildLayerList(dynamicMapServiceLayer);
}else{
dojo.connect(dynamicMapServiceLayer,"onLoad",buildLayerList);
}
} function buildLayerList(layer) {
var infos = layer.layerInfos, info;
var items = [];
for (var i=0,j=infos.length;i<j;i++) {
info = infos[i];
if (info.defaultVisibility) {
visible.push(info.id);
}
items[i] = "<input type='checkbox' class='list_item' checked='" + (info.defaultVisibility ? "checked" : "") + "' id='" + info.id +"' onclick='updateLayerVisibility();'/><label for='" +info.id+ "'>" +info.name+ "</label>";
}
dojo.byId("layer_list").innerHTML = items.join(); layer.setVisibleLayers(visible);
map.addLayer(layer); } function updateLayerVisibility() {
var inputs = dojo.query(".list_item"), input;
visible = [];
for (var i=0,j=inputs.length;i<j;i++) {
if(inputs[i].checked) {
visible.push(inputs[i].id);
}
}
dynamicMapServiceLayer.setVisibleLayers(visible); }
dojo.addOnLoad(init); </script> </head> <body >
This sample loads an ArcGISDynamicMapServiceLayer.<br />
It determines the layers in the map service and presents them as checkboxes that can be used to toggle their visibility.<br />
<br />
Layer List: <span id="layer_list"></span><br />
<br />
<div id="map" class="tundra" style="width: 900px;height: 600px;border: 1px solid #000"></div>
</body>
</html>
