Select Multiple Features

<!--
  示例：多选要素
  要点：Select 的 multi 允许累加，condition 决定哪些点击进入选中集合
  依赖：OpenLayers 10.3.1 · jsDelivr CDN（底图 OSM，无 Key）
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>多选要素</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif;color:#16181d}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:14px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar b{color:#16181d;font-weight:600}
  .bar button{font-size:12px;padding:3px 10px;border:1px solid #cfd5de;background:#fff;
              border-radius:5px;cursor:pointer;color:#16181d}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <span>点击或按住 Shift 点击累加</span>
  <span>已选 <b id="n">0</b></span>
  <span>合计面积 <b id="area">0</b> km²</span>
  <button id="clr">清空选择</button>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';
  if (!window.ol) {
    document.getElementById('map').textContent = 'OpenLayers 加载失败，请检查 cdn.jsdelivr.net 是否可访问';
    return;
  }

  var feats = [];
  for (var i = 0; i < 6; i++) {
    var lon = 116.33 + (i % 3) * 0.055;
    var lat = 39.90 + Math.floor(i / 3) * 0.045;
    feats.push(new ol.Feature({
      geometry: new ol.geom.Circle(ol.proj.fromLonLat([lon, lat]), 2600),
      name: '片区 ' + (i + 1)
    }));
  }

  var layer = new ol.layer.Vector({
    source: new ol.source.Vector({ features: feats })
  });

  /* 圆是多边形几何，标注用样式函数补上名称 */
  layer.setStyle(function (f) {
    return new ol.style.Style({
      fill: new ol.style.Fill({ color: 'rgba(47,143,91,.16)' }),
      stroke: new ol.style.Stroke({ color: '#2f8f5b', width: 2 }),
      text: new ol.style.Text({
        text: f.get('name'),
        font: '500 12px sans-serif',
        fill: new ol.style.Fill({ color: '#16181d' }),
        stroke: new ol.style.Stroke({ color: '#fff', width: 3 })
      })
    });
  });

  var map = new ol.Map({
    target: 'map',
    layers: [new ol.layer.Tile({ source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}) }), layer],
    view: new ol.View({ center: ol.proj.fromLonLat([116.385, 39.945]), zoom: 12 }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  var select = new ol.interaction.Select({
    multi: true,
    condition: function (evt) {
      /* 单击累加，再用 Shift 点击可一直追加 */
      return ol.events.condition.click(evt);
    },
    style: new ol.style.Style({
      fill: new ol.style.Fill({ color: 'rgba(214,69,69,.30)' }),
      stroke: new ol.style.Stroke({ color: '#d64545', width: 3 })
    })
  });

  function update() {
    var sel = select.getFeatures();
    var total = 0;
    var names = [];
    sel.forEach(function (f) {
      total += ol.sphere.getArea(f.getGeometry());
      names.push(f.get('name'));
    });
    document.getElementById('n').textContent = sel.getLength();
    document.getElementById('area').textContent = (total / 1e6).toFixed(2);
    document.title = names.length ? '多选要素 · ' + names.join(' / ') : '多选要素';
  }

  select.getFeatures().on('add', update);
  select.getFeatures().on('remove', update);
  map.addInteraction(select);

  document.getElementById('clr').addEventListener('click', function () {
    select.getFeatures().clear();
    update();
  });
})();
</script>
</body>
</html>