1.效果图

2.通过定义唯一值渲染器，渲染字段，设置渲染方式渲染

唯一值写死，方式设置参考官方api

//定义唯一值渲染器，对字段alias进行渲染，fill是默认的渲染符号
var renderer = new UniqueValueRenderer(fill, "name");
//设置渲染的方式
renderer.addValue("C", new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID, lineSymbol,new Color([0, 255, 0, 0.5])));
renderer.addValue("B", new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID, lineSymbol,new Color([0, 0, 255, 0.5])));
renderer.addValue("A",new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID, lineSymbol,new Color([255, 0, 255, 0.5])));
renderer.addValue("O", new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID, lineSymbol,new Color([255, 255, 255, 0.75])));
featureLayer.setRenderer(renderer);
贴代码
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
    <title>UniqueValueRenderer</title>
    <link rel="stylesheet" href="https://js.arcgis.com/3.28/esri/css/esri.css"/>
    <link rel="stylesheet" href="https://js.arcgis.com/3.28/dijit/themes/tundra/tundra.css"/>
    <script  type="text/Javascript" src="https://js.arcgis.com/3.28/"></script>
    <style type="text/css">
        .MapClass{
            width:100%;
            height:600px;
            border:1px solid #000;
        }
    </style>
    <script type="text/javascript">

        require(["esri/map",
                    "esri/layers/ArcGISDynamicMapServiceLayer",
                    "dojo/on",
                    "dojo/dom",
                    "dojo/colors",
                    "esri/symbols/SimpleFillSymbol",
                    "esri/layers/FeatureLayer",
                    "esri/symbols/SimpleLineSymbol",
                    "esri/renderers/UniqueValueRenderer",
                    "dojo/domReady!"],
                function (Map, ArcGISDynamicMapServiceLayer,on,dom,Color,SimpleFillSymbol, FeatureLayer, SimpleLineSymbol,UniqueValueRenderer) {
                    var map = new esri.Map("MyMapDiv");
                    var layer = new ArcGISDynamicMapServiceLayer("http://localhost:6080/arcgis/rest/services/demo/Practice/MapServer");
                    map.addLayer(layer);
                    //获得id为btn的DOM元素
                    var btn=dom.byId("btn");
                    //绑定相应的事件
                    on(btn,"click",function(){
                        //定义一个要素图层
                        var featureLayer = new FeatureLayer(
                        "http://localhost:6080/arcgis/rest/services/demo/Practice/MapServer/2",
                         {
                            mode:FeatureLayer.MODE_SNAPSHOT,
                            outFields: ["*"]
                         });
                        //定义线符号
                        var lineSymbol=new SimpleLineSymbol(SimpleLineSymbol.STYLE_DASH, new Color([255, 0, 0]), 3);
                        //定义面符号
                        var fill=new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID, lineSymbol,new Color("#FFFFCC"));
                        //定义唯一值渲染器，对字段alias进行渲染，fill是默认的渲染符号
                        var renderer = new UniqueValueRenderer(fill, "name");
                        //设置渲染的方式
                        renderer.addValue("C", new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID, lineSymbol,new Color([0, 255, 0, 0.5])));
                        renderer.addValue("B", new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID, lineSymbol,new Color([0, 0, 255, 0.5])));
                        renderer.addValue("A",new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID, lineSymbol,new Color([255, 0, 255, 0.5])));
                        renderer.addValue("O", new SimpleFillSymbol(SimpleFillSymbol.STYLE_SOLID, lineSymbol,new Color([255, 255, 255, 0.75])));
                        featureLayer.setRenderer(renderer);
                        map.addLayer(featureLayer);                 
                    })    
                });


    </script>
</head>
<body>
<div id="MyMapDiv" class="MapClass"></div>
<button id="btn">渲染</button>
</body>
</html>