Box Select

<!--
  示例：框选要素
  要点：DragBox 用 Shift 触发，boxend 取 extent 后遍历相交要素并换样式
  依赖：OpenLayers 10.3.1 · jsDelivr CDN
-->
<!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>框选要素</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}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:10px;align-items:center;font-size:12px;color:#58606e}
  .bar button{padding:4px 10px;border:1px solid #cfd4dc;border-radius:4px;
              background:#fff;cursor:pointer;font-size:12px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <span>按住 Shift 拖拽框选</span>
  <span id="count">已选 0 个</span>
  <button id="clear">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 (typeof ol === 'undefined') {
    document.getElementById('map').innerHTML =
      '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  var fromLonLat = ol.proj.fromLonLat;
  var features = [];

  for (var i = 0; i < 24; i++) {
    var lon = 116.362 + (i % 6) * 0.0125;
    var lat = 39.898 + Math.floor(i / 6) * 0.0095;
    features.push(new ol.Feature({
      geometry: new ol.geom.Point(fromLonLat([lon, lat])),
      name: '点 ' + (i + 1)
    }));
  }

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

  var baseStyle = new ol.style.Style({
    image: new ol.style.Circle({
      radius: 6,
      fill: new ol.style.Fill({ color: '#1f5fd0' }),
      stroke: new ol.style.Stroke({ color: '#ffffff', width: 2 })
    })
  });

  var pickStyle = new ol.style.Style({
    image: new ol.style.Circle({
      radius: 8,
      fill: new ol.style.Fill({ color: '#e8590c' }),
      stroke: new ol.style.Stroke({ color: '#ffffff', width: 2 })
    })
  });

  layer.setStyle(baseStyle);

  /* 只响应按住 Shift 的拉框动作 */
  var dragBox = new ol.interaction.DragBox({
    condition: ol.events.condition.shiftKeyOnly,
    className: 'ol-dragbox'
  });

  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: fromLonLat([116.397, 39.914]),
      zoom: 13
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  map.addInteraction(dragBox);

  var selected = [];
  var count = document.getElementById('count');

  function clearSelection() {
    selected.forEach(function (f) { f.setStyle(null); });
    selected = [];
    count.textContent = '已选 0 个';
  }

  dragBox.on('boxend', function () {
    var extent = dragBox.getGeometry().getExtent();
    clearSelection();

    source.forEachFeatureIntersectingExtent(extent, function (feature) {
      feature.setStyle(pickStyle);
      selected.push(feature);
    });

    count.textContent = '已选 ' + selected.length + ' 个';
  });

  document.getElementById('clear').addEventListener('click', clearSelection);
})();
</script>
</body>
</html>