当只加载动态图层(ArcGISDynamicMapServiceLayer)时，调用map.getZoom()方法只会返回-1，为什么呢？
由于Zoom属性是基于地图的lods属性，而动态地图服务图层并没有lods属性，此时则需人为定义map的lods来实现层级控制。
实例：
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link rel="stylesheet" href="http://192.168.2.118:8484/arcgis_js_api/library/3.20/3.20/dijit/themes/claro/claro.css">
<link rel="stylesheet" href="http://192.168.2.118:8484/arcgis_js_api/library/3.20/3.20/esri/css/esri.css">
<script src="http://192.168.2.118:8484/arcgis_js_api/library/3.20/3.20/init.js"></script>
<script type="text/javascript" src="jquery-1.10.2.min.js"></script>
<title>动态图层</title>
<script type="text/javascript">
require([
"esri/map",
"esri/layers/ArcGISDynamicMapServiceLayer",
"dojo/domReady!"
], function(
Map,ArcGISDynamicMapServiceLayer
) {
//wkid:3857
var lods = [
{ "level": 0, "resolution": 156543.03392800014, "scale": 5.91657527591555E8},
{ "level": 1, "resolution": 78271.51696399994, "scale": 2.95828763795777E8},
{ "level": 2, "resolution": 39135.75848200009, "scale": 1.47914381897889E8},
{ "level": 3, "resolution": 19567.87924099992, "scale": 7.3957190948944E7},
{ "level": 4, "resolution": 9783.93962049996, "scale": 3.6978595474472E7},
{ "level": 5, "resolution": 4891.96981024998, "scale": 1.8489297737236E7},
{ "level": 6, "resolution": 2445.98490512499, "scale": 9244648.868618},
{ "level": 7, "resolution": 1222.992452562495, "scale": 4622324.434309},
{ "level": 8, "resolution": 611.4962262813797, "scale": 2311162.217155},
{ "level": 9, "resolution": 305.74811314055756, "scale": 1155581.108577},
{ "level": 10, "resolution": 152.87405657041106, "scale": 577790.554289},
{ "level": 11, "resolution": 76.43702828507324, "scale": 288895.277144},
{ "level": 12, "resolution": 38.21851414253662, "scale": 144447.638572}
];
//wkid:4326
// var lods = [
// { "level": 1, "resolution": 0.7031249999891485, "scale": 2.958293554545656E8},
// { "level": 2, "resolution": 0.35156249999999994, "scale": 1.479146777272828E8},
// { "level": 3, "resolution": 0.17578124999999997, "scale": 7.39573388636414E7},
// { "level": 4, "resolution": 0.08789062500000014, "scale": 3.69786694318207E7},
// { "level": 5, "resolution": 0.04394531250000007, "scale": 1.848933471591035E7},
// { "level": 6, "resolution": 0.021972656250000007, "scale": 9244667.357955175},
// { "level": 7, "resolution": 0.01098632812500002, "scale": 4622333.678977588},
// { "level": 8, "resolution": 0.00549316406250001, "scale": 2311166.839488794},
// { "level": 9, "resolution": 0.0027465820312500017, "scale": 1155583.419744397},
// { "level": 10, "resolution": 0.0013732910156250009, "scale": 577791.7098721985},
// { "level": 11, "resolution": 0.000686645507812499, "scale": 288895.85493609926},
// { "level": 12, "resolution": 0.0003433227539062495, "scale": 144447.92746804963}
// ];
map = new Map("map", {
extent: initExtent,
logo: false,
slider: false,
minZoom:6,
zoom:5,
maxZoom:9,
lods:lods,
autoResize:true
});
var url="http://cache1.arcgisonline.cn/arcgis/rest/services/ChinaOnlineStreetGray/MapServer";
var layer = new ArcGISDynamicMapServiceLayer(url);
map.addLayer(layer);
//地图比例缩放结束事件
map.on("zoom-end",function(){
//弹出当前地图缩放比例值
alert(map.getZoom());
});
});
</script>
</head>
<body>
<div id="map" style="width: 100%;height:500px;border: 1px blue solid;">
</div>
<h2>世界地图ArcGISDynamicMapServiceLayer图层</h2>
<h4>针对ArcGISDynamicMapServiceLayer获取当前Zoom的值为-1的解决方法</h4>
</body>
</html>
注意：v4.7 换成了view.constraints.lods = lods;
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